Western Hemlock Bark an Important Potential Tanning Materiau

Technical Bulletin No. 566 April 1937

UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C.

WESTERN HEMLOCK BARK AN IMPORTANT POTENTIAL TANNING MATERIAU

By CHARLES C. SMOOT, tanning technologist, and RALPH W. FREY, senior chemist. Industrial Farm Products Research Division, Bureau of Chemistry and Soils

CONTENTS

Page Page Foreword.. 1 Extraction and yield of tannin 26 Introduction _ 2 Large-scale test 26 Western hemlock bark 5 Laboratory runs 27 Botanical range of western hemlock 7 Optimum conditions 30 Visible supply 8 Extract production 30 Physical characteristics 9 Methods compared 31 Properties of the various extracts 32 Tannin content 10 Recommended procedure 33 Factors influencing availability 12 Tanning with bark extract 34 Mechanical peeling .... 13 Laboratory experiments 34 Deck peeling 14 Large-scale tanning tests 35 Woods peeling 16 Quality and analyses of hemlock leathers. _ 36 Woods curing 17 Adequate initial production necessary for suc- Seasonal variation in tannin content 18 cessful utilization, introduction, and market- Artificial drying •_ 19 ing _ 37 Experimental test runs 20 C apital requirement and operating costs 40 Test runs by manufacturers 21 Probable selling price of extract 42 Large-scale drying tests. 22 Summary 43 Optimum conditions 26 Literature cited 46

FOREWORD This bulletin presents a survey and study by the late Charles C. Smoot of the salvaging of tanning extracts from hemlock bark now not utilized in lumbering and pulp production in the Pacific coast region. The survey and most of the experimental studies were made under the general supervision of F. P. Veitch, then Principal Chemist in charge of the Industrial Farm Products Division. At the time of his death Mr. Smoot was employed as a tanning technologist in the Bureau of Chemistry and Soils. As chemist, tanner, and general manager, respectively, he had formerly been connected for 16 years with C. C. Smoot & Sons Co., North Wilkes- boro, N. C, tanners of sole leather and manufacturers of tanning extracts. The data, estimates, and conclusions of this bulletin are conservatively presented in the light of Mr. Smooths extensive experience and intimate practical knowledge of the tanning of leather and the production of tanning extracts. 1 Received for publication Nov. 18, 1936. 121729°—37 1 2 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE Thanks are extended especially to T. T. Munger, director of the Pacific Northwest Forest Experiment Station, Portland, Oreg., and his staff for their ready counsel and able assistance in the conduct of these studies; and to F. W. Mathias, manager of the Grays Harbor Chamber of Commerce, Aberdeen-Hoquiam, Wash., and Dean G. W. Peavy, of the School of Forestry, Oregon State College, Corvallis, Oreg., for their services and many kindnesses, particularly for their wholehearted cooperation in the work on artificial bark drying. The helpful cooperation of the following individuals and firms is also gratefully acknowledged: Chamber of Commerce of Portland, Oreg., Grays Harbor Chamber of Commerce, Aberdeen-Hoquiam, Wash., Longview Chamber of Commerce, Longview, Wash., Chamber of Commerce, Tacoma, Wash., State Forest Service, Salem, Oreg., School of Forestry, Oregon State Agricultural College, Corvallis, Oreg., Minister of Lands, British Columbia, West Coast Lumber- men's Association, Western Forestry and Conservation Association, British Columbia Loggers Association, Bloedel Donovan Lumber Mills, Crown Willamette Paper Co., Long-Bell Lumber Co., Longview Co., M. & M. Plywood Co., Plylock Corporation, S. E. Portland Lumber Co., Weyerhaeuser Timber Co., Willamette Valley Lumber Co., Alt Bros., Donald W. Lyle, Oakex Co., Philadelphia Drying Machinery Co., Proctor & Schwartz, Inc., Buffalo Foundry & Machine Co., Douthitt Corporation, Philadelphia Coppersmithing Co., Sharpies Specialty Co., Western Precipitation Co., American Oak Leather Co., Dreuding Bros. Co., Good Bros. Leather Co., International Shoe Co., Leas & McVitty, Inc., and United States Leather Co. HENRY G. KNIGHT, Chief, Bureau of Chemistry and Soils.

INTRODUCTION Tannins occur in the bark, wood, leaves, roots, and fruits of plants. In their natural form and as prepared extracts they are used in large quantities as one of the essential raw materials of the leather industry. Although the tannins are widely distributed in the vegetable king- dom, comp'aratively few plants contain sufficient tannin to permit their successful utilization as commercial sources of this product. There are at present in the United States only three outstanding developed sources of tannin. These are the wood of the American chestnut tree and the barks of the chestnut oak and eastern hemlock. Sumac leaves, the bark of the California tanbark oak, and extracts prepared from waste sulphite liquors of the paper industry con- tribute also to a less extent to our domestic supply of tanning materials. The important tanning materials and the total annual consumption of tannin in this country by the leather industry are shown in table 1. These data have been calculated from reports by the United States Bureau of the Census (18)^ on the consumption of tanning materials. The figures show the net weight of actually available tannin from the raw material and extract in each case and not the total or bulk weight of the tanning material. They have been expressed in this way to provide comparisons on the common basis of actual tannin, 2 Italic numbers in parentheses refer to Literature Cited, p. 46. TABLE L--Consumptior . of tannin hy tanneries in the United States in stated years ^

1923 1925 1927 1929 1931 a Proportion— Proportion— Proportion— Proportion— Proportion— Tan- Tan- Tan- Tan- Tan- nin 2 nin 2 nin 2 nin 2 nin 2 Of Of Of Of Of Of Of Of Of Of group total group total group total group total group total

O Domestic group: Tons Percent Percent Tons Percent Percent Tons Percent Percent Tons Percent Percent Chestnut wood Tons Percent Percent O 55, 301 60.9 36.2 41, 006 60.1 35.0 38, 853 59.0 32.9 39, 318 64.9 35.5 24, 784 61.8 31. 0 Chestnut oak bark 17, 679 19.4 11.6 11, 168 16.4 9.5 12, 927 19.6 10.9 9,283 15.3 8.4 Eastern hemlock bark_ _ _ 7,525 18.8 9.4 16, 456 18.1 10.8 15, 326 22.4 13.1 13, 156 20.0 11.1 10, 693 17.7 9.6 7,076 17.6 8.9 td Sulphite cellulose 1,241 1.4 .8 789 1.1 . 7 911 1.4 .8 1,299 2.1 1.2 All others 562 1.4 .7 > 151 .2 .1 180 .4 .2 Total 90,828 100.0 59.5 68, 289 . 100.0 58.3 65, 847 100.0 55.7 60, 593 100.0 54.7 40,127 100.0 50.2 Foreign group: Quebracho wood 40, 274 65.0 26.4 34, 139 70.0 29.1 37, 803 72.3 32.0 34, 967 69.6 31.5 Myrobalan nuts 26, 678 67.2 33.4 5,929 9.6 3.9 1,966 4.0 1.7 3,950 7.5 3.3 4,214 8.4 3.8 2,299 5.8 2.9 o Wattle bark 4,746 7.7 3.1 2,236 4.6 1.9 2,650 5. 1 2.3 H Valonia cups and beard 2,915 4.7 1.9 2,707 5.5 2.3 2,034 3.9 1.7 } 3, 621 7.4 3.3 3,631 9.1 4.5 Mangrove bark 1,927 3.2 1.2 1,177 2.4 1.0 2.027 3.8 1.7 3,769 7.5 3.4 4,291 10.8 5. 4 Sumac leaves . 1,806 2.9 1.2 1,123 2.3 1.0 1,199 2.3 1.0 1,303 2.5 1.2 H Divi-divi pods 983 2.5 1.2 1,785 2.9 1.2 394 .8 .3 468 .9 .4 124 .2 .1 49 .1 . 1 Gambier leaves and twigs 822 1.3 .5 406 .8 .4 327 .6 .3 364 .7 .3 > All others 297 .4 1,700 2.7 1.1 4,701 9.6 4.0 1,868 3.6 1.6 1,869 3.7 1.7 1,501 3! 8 1.9 Total H 61, 904 100.0 40.5 48, 849 100.0 41.7 52, 326 100.0 44.3 50, 231 100.0 45.3 39, 729 100.0 49.8 Total domestic and foreign 152, 732 100.0 117,138 100.0 118,173 100.0 110, 824 100.0 79, 856 100. 0 h-t 1 Similar data not available for 1933. 2 Available tannin in raw materials and extracts, expressed in short tons. o

00 4 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE Table 1 shows that only slightly more than half our total supply of tannin is derived from domestic materials. Quebracho wood is the outstanding foreign material, contributing about 30 percent of our total supply and 70 percent of all foreign supplies. Of our limited number of native materials chestnut wood alone furnishes more than 60 percent of our domestic supply of tannin. This is most pertinent. The American chestnut tree is being steadily exterminated by the chestnut blight, which is now established throughout the entire chestnut belt. For the 5 years shown in table 1 the average total annual consumption of tannin was 115,745 tons, equivalent to 462,980 tons of 25-percent extract. Economists frequently use 1926 statistics as a reference for comparing current data with those of more normal periods. For 1925 and 1927, the 2 years nearest to 1926, the total tannin consumption was 117,138 tons and 118,173 tons, respectively. On the basis that the United States uses about one-half the world's production of tannin, these data indicate an annual world requirement of over 235,000 tons of tannin, or 940,000 tons of 25-percent extract. Tanning, or the conversion of hides and skins into leather, may be done in many ways. However, over 90 percent of all commercial leathers can be classified as either vegetable- or mineral-tanned. The first type is made with tannin, hence the name vegetable leather or vegetable-tanned. The second type is made with compounds of chromium, aluminum, iron, and the like, and is therefore called mineral-tanned. These two tannages produce leathers of distinctly difl*erent characteristics, so that either one or the other, or sometimes combinations of the two, are used to secure the commercial leather best adapted for the use intended. The rather general practice has become established of using mineral tannages for producing most of the light leathers, especially shoe upper and glove leathers. The heavy leathers, comprising sole, belting, harness, case, bag, and strap leathers, are usually vegetable-tanned, as are also hat and fancy leathers. Statistics showing the quantity of vegetable-tanned leather annually produced in this country are not available. A rough estimate of the quantity of this class of leather made yearly is presented in table 2. These figures have been calculated from reports of the Bureau of the Census (17) on the leather industries, using a list of vegetable-tanned leathers compiled by the Tanners' Council of America and estimated average weights for the various commercial trims, splits, and pieces of leather.

TABLE 2.—Estimated annual production of vegetable-tanned leather in the United States in stated years

Proportion Proportion of total of vege- Total vege- Vegetable- vegetable- table- table- tanned tanned tanned Year tanned heavy leather heavy leather leather i that is leather heavy that is leather sole leather

1,000,000 lbs. 1,000,000 lbs. Percent Percent 1923 530 450 85 80 1925 420 350 83 81 1927 470 390 83 78 1929 450 365 81 77 1931 370 290 78 86 1933 320 260 81 86 Average -- - 427 351 82 81

I Includes sole, belting, harness, case, bag, and strap leathers. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 5 Practically 95 percent of the heavy leather made in this country is vegetable-tanned. The vegetable tannins are therefore important and essential materials for the leather industry in the production of leather goods that are daily necessities in the lives of everyone in this country and prime requisites in times of national emergency. Their use for this purpose has long been established, and there is no sugges- tion at present of their being supplanted as the principal tanning agents for the heavy leathers. Not only are our recognized sources of tannin limited, but inroads upon them by man and disease are steadily making for their exhaustion. For these reasons it is important and timely that serious consideration be given to possible undeveloped domestic supplies and to the creation of new sources. With this objective, attention has been centered for the time being upon a material appearing to have potentialities for the purpose in mind and occurring in tremendous quantities in the extreme northwestern portion of the United States and nearby Canada, namely, the bark of western hemlock, Tsuga heierophylla. The purpose of this study is to present a survey of the problems and numerous factors involved in the utilization of this bark, from which those who may be interested can draw deductions concerning the commercial feasibility and promise of success in the development of western hemlock bark as a domestic tanning material.

WESTERN HEMLOCK BARK The existence of extensive stands of hemlock in the Pacific coast region has been well known for many years. As long as 40 years ago farsighted individuals of the leather industry became interested in the tanning properties of the bark of this tree, and especially in ascertaining its similarity, if any, to the bark of the hemlock (Tsuga canadensis) found throughout the eastern section of the United States and Canada, which bark had been and was than one of the two principal sources of tannin on which the American tanning industry of that day depended. The results of these investigations were not published, and there is no record of any serious attempt by tanning interests to bring about a commercial development of western hemlock bark as a source of tannin, even though it is understood that investigation showed the existence of enormous quantities of a bark possessing tanning properties quite similar to those of eastern hemlock bark. There were several important underlying reasons for the lack of further developments at that time. (1) The high cost of transporting the tanning material in usable form to the tanneries, most of which were located close to the Atlantic seaboard, was the most serious handicap. Under the conditions existing then the cured bark itself or a liquid extract containing about 25 percent of tannin were the only recognized means of getting the tannin to the tanneries. To transport these comparatively dilute tannin products 3,000 miles by rail, or 14,000 miles by boat around South America, was prohibitive. (2) When gaged by the conditions and practices of gathering hemlock and oak barks in our eastern forests, the tremendous size of the hemlock trees of the Pacific coast, the heavy undergrowth found with this timber, and the heavy rainfall in the areas of supply constitute serious handicaps to be overcome. TECHNICAL BULLETIN 5(î6, Ü. B. DEPT. OF AGRirULTTTRE (3) The familiar eastern hemlock bark is comparatively thick, aver- aging IK inches, and oak bark is even thicker. The tannin content, however, is only about 11 percent for hemlock and 12 percent for i:^^

PA CIFl C OCEAN

¡BOTANICAL RANGE

MILES 0 200 1 I II >i ill

FIGURE 1.—Botanical range of western hemlock (Tsuga heterophylla). (Prepared by the U. S. Forest Service.) chestnut oak. In contrast to this the hemlock bark of the Pacific coast region averages only about five-eighths of an inch in thickness. Its tannin content, however, is around 15 percent. This higher tannin content would appear to have been lost sight of or not accepted as WESTERN HEMLOCK BARK A POTENTTAL TANNING MATERTAL 7 true, merely because of the unusual thinness of this bark as compared with the tanbarks then in use. (4) The demand for additional supplies of tanning materials was being niet by the introduction of two new tanning extracts, one from domestic chestnut wood and the other from imported quebracho wood, supplemented by an increasing use of the then newly developed chrome tannage, particularly in the production of light leathers. The introduction of these two extracts led to the adoption of the European practice of using blends of tannins from several materials rather than the use entirely of either oak bark or hemlock bark, which had been essentially the American practice up to that time. Some Ameri- can tanners had experimented in the use of a blend composed of equal quantities of oak bark and hemlock bark, the leather produced being known as '^union'', but this was not a general practice. While these reasons suiRce to explain inactivity in this early period, they do not explain the continued lack of development of western hemlock bark up to the present. The building of the Panama Canal, the establishment of intercoastal transportation at low cost, and mod- ern developments in the production of tanning extracts containing but little moisture have reduced materially the handicap of high transportation costs, but apparently not suiBciently to offset the lower cost of tanning materials from foreign products rich in tannin, coupled with the increasing tendency to use blends from a number of raw materials. The establishment of a tanning industry centered around San Fran- cisco and based on the use of native California tanbark oak led to the erection about 1892 of a small extract plant in Clallam County, Wash., for operation with western hemlock bark. This venture probably was doomed to failure from the start because of insufficient capital and technical knowledge of majiufacture and marketing, together with the great distance necessary to transport the product. It is 1,000 miles from Clallam Bay, where the extract plant was located, to San Francisco Bay, where the tanneries were. However, this plant went out of business during the economic depression of 1893, and by the time conditions had again become normal the quebracho- and chestnut-extract industries were well established and were supplying the demand at reasonable cost. The knowledge that tremendous quantities of this bark occur within the borders of the United States as offal from the cutting of western hemlock has kept this subject alive. The possibilities of utilizing this bark have been discussed from time to time by government agen-, cies and others (1, 2^ 3, 5, 8, 10, 11, 13, 15) interested in conservation work, but no commercial development has actually materialized.

BOTANICAL RANGE OF WESTERN HEMLOCK Western hemlock, Tsuga heterophylla^, is found along the Pacific coast from Prince William Sound in Alaska to northern California, and as far inland as northern Idaho and northwestern Montana (fig. 1). The best stands are in the humid coastal regions of Oregon, Wash- ington, British Columbia, and Alaska and on the lower slopes of the Cascade Range in Washington, Oregon, and southern British Colum- bia, at elevations of 1,500 to 3,500 feet. This species grows best in

3 UNITED STATES DEPARTMENT OF AGRICULTURE, FOREST SERVICE, WESTERN HEMLOCK. AMERICAN WOODS. 5pp.,illus. 1934^ [Multigraphed.] 8 TECHNICAL BULLETIN 566, Ü. S. DEPT. OF AGRICULTURE cool, moist locations and occasionally reaches an age of 500 years. Trees 100 years old are generally 17 to 21 inches in diameter and 130 to 150 feet in height. Under favorable conditions mature trees reach a diameter of 3 to 4 feet and a height of 175 to 225 feet. Tsuga heterophylla (16) usually is associated with Douglas fir, western red cedar, and Sitka spruce. Sometimes it is the dominant- tree, especially in Alaska, where nearly pure forests of this species are found. The name western hemlock should not be confused with Tsuga canadensis of the North Central States and Canada, the bark of which is frequently but erroneously referred to in the tanning and extract trades as western hemlock to differentiate it from the hemlock of Pennsylvania, West Virginia, and other eastern sections.

VISIBLE SUPPLY In 1929 it was estimated by the United States Forest Service ^ that there were some 150 billion board feet of western hemlock distributed as follows in the United States and Alaska: Board feet Alaska 63,000,000,000 Washington 60,000,000,000 Oregon. 25,000,000,000 Idaho, Montana, and California 2,000,000,000 To this may be added about 60 billion board feet in British Colum- bia (7), making a total of 210 billion board feet. Later forest surveys (14) show 105 billion feet of western hemlock (16 inches and up in diameter at breast height) in Washington and Oregon. The total annual cut of western hemlock, however, has been steadily increasing until in 1929 it was estimated at 1,600,000,000 board feet.^ It is now the most important pulpwood of the Pacific Northwest. When considered in connection with the present enormous stand, the rate of reproduction is sufficiently rapid to warrant the statement that with the use of conservation methods a perpetual supply appears to be assured. Data on yield of bark per tree are not available from actual practice. Hanzlik and Oakleaf (10), however, have prepared tables based on the thickness of the bark at different heights of the tree that are useful in estimating yields of bark. Their data are reproduced in part in tables 3 and 4. For equivalents in terms of cords, 66.6 cubic feet (solid measure) has been taken as equal to 2,000 pounds and 77 cubic feet (solid measure) as equal to 2,240 pounds.

• 4 UNITED STATES DEPARTMENT OF AGRICULTURE, FOREST SERVICE. See footnote 3, p. 7. WEKSTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 9

TABLE 3.— Yield of Western hemlock hark per tree *

[Bark collected on lower slope of the Cascade Mountain area and utilized to a point 8 inches in diameter inside the bark]

On basis of 2,000 pounds per On basis of 2,240 pounds per cord cord Diameter of sDtiLtL. ¡JKL 11 ee Second Second tree at breast Old growth Old growth height growth growth (inches) Sec- Sec- Bark Trees Bark Trees Bark Trees Bark Trees ond Old Old growth ond growth per per per per per per; per per growth growth tree cord tree cord tree cord tree cord

Cubic Cubic Num- Num- Num- Num- Feet Feet feet feet Cords ber Cords ber Cords ber Cords ber 12 120.0 87.0 4.80 3.70 0.07 14.3 0.06 17.8 0.06 16.6 0.05 20.8 14 133.5 106.0 7.25 5.60 .11 9.1 .08 11.9 .09 11.1 .07 13 7 16 145.0 117.0 9.80 8.20 .15 6.7 .12 8.1 .13 7.7 .11 9 4 18 154.0 130.0 12.40 11.80 .19 5.3 .18 5.7 .16 6.2 .15 6.5 20 160.5 138.0 15.35 15.80 .23 4.3 .24 4.2 .20 5.0 .20 4.9 22 164.0 145.0 18.55 20.40 .28 3.6 .31 3.3 .24 4.2 .26 3.8 24 166.0 150.0 22.05 25.30 .33 3.0 .38 2.6 .29 3.4 .33 3.0 26 167.0 154.0 26.00 30. 30 .39 2.6 .45 2.2 .34 3.0 .39 2 5 28 168.0 158.0 30.00 35.20 .45 2.2 .53 1.9 .39 2.6 .46 2 2 30 168.0 161.0 34.00 40.30 .51 2.0 .60 1.7 .45 2.2 .52 1.9 32 165.0 45. 20 .68 1.5 .59 1.7 34_ _ 169.0 50.20 .76 1.3 .65 1 5 36 174.0 55.30 .83 1.2 .72 1.4 38 178.0 60.70 .91 1.1 .79 1 3 40 183.0 66.50 1.00 1.0 .86 1.2 42 188.0 73.00 1.10 .9 .95 1 1 44 193.0 80.20 1.20 -.8 _ 1.04 1.0 46 198.0 88.00 1.32 .8 1.14 .9

1 From Hanzlik and Oakleaf (10).

TABLE 4.— Yield of western hemlock bark per acre from pure second-growth and pure mature stands ^

[Bark utilized to a point 8 inches in diameter inside the bark]

On basis of 2,000 On basis of 2,240 pounds per cord pounds per cord Bark per Bark per Locality Character of stand thousand thousand Bark per feet of lum- Bark per feet of lum- acre ber (board acre ber (board measure) measure) Cords Cords Cords Cords Pilchuck Block, Wash.. Second growth. 30.31 0.28 26.44 0. 25 Aloha, Wash Old growth 38.28 .32 33.21 .28 Cathlamet, Wash do 31.26 .27 27.06 .24

1 From Hanzlik and Oakleaf (10). The cord used in standard practice for Ijark is 128 cubic feet mea- sured after piling and should not be confused with solid measure. Although the cord is the standard measure, cured bark is generally sold by weight in order to eliminate variations caused by piling. Through- out the East, a cord of hemlock bark is usually 2,240 pounds, but in some sections of the country and in railway tariffs 2,000 pounds is standard. On the Pacific coast 2,300 pounds seems to be the usual weight for a cord of bark.

PHYSICAL CHARACTERISTICS Western hemlock bark is similar in general appearance and structure to the well-known eastern variety. The principal differences are in the ross and depth of furrows. Western hemlock bark has propor- tionally a thinner ross and shallower furrows than eastern hemlock 121729°—37 2 10 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE bark. It averages about five-eighths of an inch in thickness, as against IK inches for bark of the eastern hemlock. A close-up picture of well-cured prime bark of western hemlock is shown in plate 1.

TANNIN CONTENT From various sources data are available on the tannin content of western hemlock bark. Collectively these cover a period from 1893 to 1934 and include bark from trees growing at elevations ranging from sea level up to 3,500 feet and from nine counties in Washington and four in Oregon. Among the first analyses are those by Wiley (3), when chemist of the United States Department of Agriculture, and Taber (1) of the Ameri- can Extract Works at Port AUegany, Pa. Wiley reported 16 percent of tannin in hemlock bark from Ashford, Wash., and 14.86 percent in bark from Enumclaw, Wash. In a comparison of hemlock bark from several sources Taber reports 17.04 percent of tannin in that from Washington. The first part of table 5 gives the analyses by the laboratory of the Elk Tanning Co., Ridgway, Pa., of 26 samples of bark collected in 1909 and 1910 by G. W. Child. These data show a tannin range from 9.3 to 19.0 percent, with an average of 13.6 percent. A number of the samples evidently were not air-dried before being shipped, as shown by their high moisture content on receipt at the laboratory. In almost every instance a high moisture content as received is associated with a comparatively low tannin figure, indicative of loss of tannin from molding of the bark. On this account the average tannin content is a little low for prime bark.

TABLE 5.— Tannin content of western hemlock hark ^

[All results on moisture-free basis]

1 Mois- ture Solu- Non- Eleva- con- Total Insolu- Tan- Date collected Location ble tannin tion tent solids solids bles nins as received

Ft. Pet. Pd. Pd. .Pd. Pd. Pd. Everett, Wash.2 31.4 27.7 3.7 10.9 16.8 August 1909 do 3 21.5 18.7 2.8 7.8 10.9 ..do 4 24.1 20.4 3.7 6.9 13.5 King County, Wash., sec. 35, T. "2,"ÓOÓ" "'Ú'.l' 29.1 24.3 4.8 8.3 16.0 23N., R. 7E. Pacific County, Wash., sec. 5, 300 19.0 21.0 17.0 4.0 6.5 10.5 T. 13N., R. 9W. Pacific County, Wash., sec. 23, 300 31.5 25.2 20.9 4.3 8.3 12. T. 13N., R. 9W. Pacific County, Wash., sec. 11, 700 30.5 28.2 21.6 6.6 6.9 14.7 T. 13 N., R. 9 W. August 1910 < ..._do 700 38.5 24.3 19.6 4.7 7.3 12.3 Pacific County, Wash., sec. 6, 350 29.0 23.2 19.3 3.9 7.1 12.2 T. 13 N., R. 9 W. Pacific County, Wash., sec. 10, 0 29.5 21.6 18.4 3.2 7.7 10.7 T. 13N., R. low. Skamania County, Wash., sec. 2,000 17.0 29.2 27.1 2.1 9.2 17.9 —, T. 5N., R. 7E. do 2,000 20.0 27.4 24.8 2.6 7.6 17.2 -—do 2,000 16.5 29.3 25.9 3.4 8.0 17.9 1 Analyses of samples collected in 1909 and 1910 were made by tne Elk Tanning Co., and supplied through the courtesy of the late W. K. Alsop of the United States Leather Co, 2 Thin bark from tannery bark shed. 3 Thick bark from tannery bark shed. 4 Extra thick bark from tannery bark shed, WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL H

TABLE 5.— Tannin content of western hemlock hark—Continued

[All results on moisture-free basis]

Mois- ture Eleva- con- Total Solu- Non- Date collected ble Insolu- Tan- tion tent solids bles tannin as re- solids nins ceived

Ft. Pet. Pet. Pet. Pet. Pet. Pet. Skamania County, Wash., sec. 2,200 18.0 30.4 26.1 4.3 8.2 17.9 12, T. 4N., R. 6E. -.-do 2,200 16.0 31.8 28.4 3.4 19.0 Linn County, Oreg., sec. 4, T. 10 2,500 16.0 23.8 22.8 LO 7.5 15.3 S., R.4E. -.-do 2,500 17.0 25.0 2L0 4.0 7.8 13.2 August 1910- do. 2,500 16.0 26.4 22.0 4.4 8.2 13.8 Yamhill County, Oreg., sec. 17, 2,200 24.0 19.7 16.2 3.5 6.5 9.7 T. 2S., R. 6W. Yamhill County, Oreg., sec. 20, 3,000 35.5 25.5 2L1 4.4 9.2 1L9 T. 2S., R. 6W. Yamhill County, Oreg., sec. —, 2,000 2L0 28.7 24.3 4.4 8.9 15.4 , T. 12N., R. 6W. Jefferson County, Wash., sec. 7, 500 25.0 24.5 19.5 5.0 7.8 n.7 T. 25N., R. 12W. -do 500 27.0 19.9 16.3 3.6 6.2 10.1 September 1910... (-..do 500 31.0 24.7 20.4 4.3 8.3 12.1 — .do 400 34.0 23.1 17.8 5.3 6.8 n.o Jefferson County, Wash., sec. —; 700 23.0 17.8 14.6 3.2 5.3 , T. 26N., R. 9W. Average.

'Grays Harbor County, Wash., 500 34.3 26.4 22.7 3.7 8.6 14.1 sec. 6, T. 12 N., R. 10 W. ----do 500 35.0 22.6 20.1 2.5 7.8 12.3 ---do 500 34.6 24.0 19.5 4.5 7.7 11.8 May 1932.. -.-do 500 34.1 25.8 22.3 3.5 8.3 14.0 --do 1,000 12.0 36.3 32.9 3.4 10.9 22.0 Cowlitz County, Wash 2,000 n.7 24.1 20.8 3.3 6.3 14.5 Grays Harbor County, Wash... 200 17.6 29.1 25.8 3.3 9.3 16.5 do 200 18.7 28.1 24.4 3.7 8.0 16.4 rciallam County, Wash 800 19.3 28.6 24.7 3.9 9.4 15.3 I..--do 800 20.2 27.4 23.9 3.5 8.8 15.1 Lincoln County, Oreg 19.8 24.1 21.0 3.1 7.7 13.3 do 15.7 24.7 21.3 3.4 8.2 13.1 Grays Harbor County, Wash., 1,000 38.2 27.8 25.4 2.4 9.3 16.1 near north fork, Quinault River. July 1932. ..-do 1,500 37.3 24.6 2L2 3.4 8.9 12.3 do. 2,000 42.7 3L3 28.6 2.7 ILl 17.5 do. 2,500 42.8 26.9 24.0 2.9 8.6 15.4 .do- 3,000 35.0 32.0 27.0 5.0 10.2 16.8 .do.. 3,500 31.4 34.1 26.8 7.3 8.3 18.5 Pacific County, Wash 200 13.4 30.1 26.8 3.3 10.0 16.8 ..-do 200 13.4 33.6 29.1 4.5 10.3 18.8 ..-do— 200 13.2 30.0 26.5 3.5 9.1 17.4 ..-do . 200 13.5 30.5 26.1 4.4 9.3 16.8 -.-do 200 14.3 27.0 23.7 3.3 9.5 14.2 —do 200 13.9 29.3 24.7 4.6 8.4 16.3 --.do 200 15.4 29.1 25.0 4.1 8.4 16.6 May 1934.. Wahkiakum County, Wash,, 2,500 n.3 24.9 22.1 2.8 8.4 13.7 sec. 8, T. ION., R. 5W. ..--do 2,500 1L2 24.0 2L9 2.1 13.1 .---do 2,500 10.5 23.7 2.9 8.7 15.0 Clackamas County, Oreg., sec. 1,500 10.9 23.6 3.0 8.0 15.6 9, T. 2S., R. 5E. -.-do 1,500 10.2 30.0 26.4 3.6 16.5 L.-.do 1,500 10.4 29.4 25.9 3.5 16.0 Average. 28.0 24.4 3.6 15.5

In the course of the present study a large number of samples, most of which were collected by the senior author, have been analyzed. The official methods of the American Leather Chemists' Association were used (4). In the lower part of table 5 are analyses on the 12 TECHNICAL BULLETIN 5()6, U. S. DEFT. OF AGRICULTURE moisture-free basis of 31 samples of western hemlock bark.^ The tannin content of the bark ranged from 11.8 to 22 percent, with an average of 15.5 percent. Except as subsequently noted, all the bark samples were thoroughly air-dried before being shipped to the laboratory. The first four samples from sec. 6, T. 12 N., R. 10 W., Grays Harbor County, Wash., were put in airtight glass containers immediately after peeling and mailed to Washington, D. C. All four samples were low in tannin, and the lowest one, 11.8 percent, was definitely molded. The six samples from the north fork of the Quinault River, Grays Harbor County, Wash., were placed in sealed containers with thymol crystals as soon as peeled, and although their moisture content was as high when received at the laboratory they were not moldy and their tannin content was above the average. The foregoing data clearly establish that western hemlock bark has a high tannin content, a fair average value in the moisture-free bark being 15.5 percent. Benson, Thompson, and Wilson (6) state: ''Generally speaking it may be said that the western hemlock excepting the western spruce is the richest source for tanning materials in the United States.'^ FACTORS INFLUENCING AVAILABILITY The bark of western hemlock is a byproduct from the cutting of timber for lumber and pulp. The wood of this tree has superior mechanical, physical, and chemical properties, as compared with the wood of the hemlock of the eastern forests. Its rating of mechanical working quahties, based on Douglas fir as 100, is 88 (9), Eastern hemlock rates 66. With a growing appreciation of its value as lumber there has been simultaneously an increase in its use for the production of pulp, with the result that the proportion of hemlock timber cut each year has recently been gaining. The Forest Service^ reports that in 1908 the cut of western hemlock lumber was only 0.2 percent of the total cut of all species for that year. By 1927, however, the cut amounted to 1,417,000,000 board feet or about 4 percent of the total cut of all species. Of this cut, 89 percent came from Washington and 10 percent from Oregon. In 1926 the consumption of western hemlock for pulpwood was equivalent to 147,000,000 board feet. This is about 28 percent of the total hemlock pulpwood consumption and over 4 percent of the total pulpwood consumption of the United States. Hodgson (12) in referring to western Oregon and Washington says: The sawmills of this region in 1929 produced 1,484,350,000 feet b. m. of western hemlock lumber. The logs used in the manufacture of this product carried about 21,760,000 cubic feet (solid measure) of bark, all of which was discarded as waste. From figures furnished by the Forest Service for 1931 it is estimated that the hemlock timber cut for pulpwood carried about 80,000 cords of bark, which added to the 330,000 cords on that cut for lumber gives more than 400,000 cords of bark annually. However, according to present practices a major portion of this bark is not now available in a form suitable for producing tanning extract, as will be brought out later. 4 UNITED STATES DEPARTMENT OF AGRICULTURE, FOREST SERVICE. See footnote 3, p. 7. Technical Bulletin 5ó6. Ui &• Dspartincnt oí A^rKulturc PLATE 1

PRIME BARK OF WESTERN HEMLOCK. A, Koss side. B, Cut edse. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL ^3

MECHANICAL PEELING The bark is removed from the logs by two general procedures. One involves machinery, such as revolving knives, revolving studded disks, or drums in which the logs are tumbled. Bark taken off in this way is referred to as mechanically removed. The other procedure is hand peeling. This may be done on log-peeling decks or at transfer rollways,in both of which cases the bark will be referred to as deck peeled ; or the bark may be taken off in or near the woods and is known as woods peeled. Most of the bark is at present removed mechanically and comes chieñy from logs cut for lumber. In general the logs are transported by cars either directly to the log pond of the sawmill, or to some location where they can be assembled into rafts for floating by water to the sawmill. In either case the logs are dumped into water. From the pond the logs suitable for lumber are moved by chain conveyors to the saw carriage and pass en route under high-pressure water sprays to wash off mud and dirt. At the saw carriage the log is squared by removal of slabs. The slabs, with adhering bark, are cut into billets for making pulp. The bark is removed from these pieces mechanically, usually by revolving knives. The portion removed by these mechanical methods is a mixture of bark and wood in the form of a wet mass. It has little value for any purpose and is usually sent to refuse burners or added to ''hogged'^ fuel. Samples of this general type of bark and wood mixtures were obtained from six different operations and air-dried before shipment. After quartering, each sample was separated as nearly as possible into wood and bark portions, or these two and a third portion consisting of unseparable wood and bark. ^ The analyses of these portions on the moisture-free basis are given in table 6.

TABLE 6.- -Tannin content of mechanically removed wood and hark mixtures of western hemlock [All results on moisture-free basis]

Sample Total Insol- NaCli Composition of sample solids ubles Tannin

Percent Percent Percent Percent Separated wood . 7.4 1.0 1.3 1.08 47203 Separated bark . 21.0 2.9 8.0 1.88 Calculated composite (wood, 54 percent; bark, 46 percent) 13.1 L8 4.4 1.45 47204 Mixture (wood,2 65 percent; bark, 35 percent) 1.4 3.3 .15 47311 Mixture (wood,2 68 percent; bark, 42 percent) 13.5 2.2 6.0 .00 '47313 Mixture (wood,2 68 percent; bark, 32 percent) 9.1 1.2 2.9 .00 Separated wood 4.7 .6 .8 Separated bark 18.7 2.7 10.5 Unseparable mixture 6.9 .8 2.8 Calculated composite (wood,241 percent; bark, 59 percent) 13.0 1.8 6.5 Separated wood 4.4 .5 .9 Separated bark 15.8 2.9 8.4 Unseparable mixture 6.8 1.0 2.5 Calculated composite (wood,2 59 percent; bark, 41 percent) 9.1

1 Total chlorides expressed as NaCl taken up from salt-water pond. 2 Estimated. The data in table 6 clearly show that this mixture has no value as a source of tannin, the tannin content ranging only from 2.9 to 6 percent. This is chiefly because the wood, which comprises ordinarily 14 TECHNICAL BULLETIN t)C6, U. S, DEPT. OF AGRICULTURE more than lialf the mixture, contains practically no tannin. There is another factor usually involved, which probably explains the low tannin content shown for the separated bark portions. According to present handling, this meclianically removed mixture is almost always from logs that liave been in water for comparatively long periods because of rafting and storing in ponds. All the samples in table 6 were from such logs. The number of days that the logs had been in water could not be ascertained, but probably it was not less than 45 in any case. All bark removed mechanically as just described must ac- cordingly be classed as unavailable as a source of tannin. Since approximately three-fourths of the bark is now removed in this way it is important that modification of present procedures to provide for removal of the bark in a usable form be given careful consideration. From this study it appears that in about half the present operations suitable changes can be made without increasing logging costs more than the value of FIGURE 2.—Deck peeling ot bark. the bark recovered. These changes would provide for passage of the logs over peeling decks or transfer rollways where the bark could be removed by hand spudding, or possibly by compressed air. DECK PEELING Deck peeling (fig. 2) is now practiced on many of the logs used for pulp before the logs are broken down. The bark is cut through at 4-foot intervals and then split lengthwise from one cut ring to the other. A spud blade is inserted between the bark and wood, and the bark is forced off by prying. This operation can be carried on only with timber cut during the time of the year when the sap is flowing freely. In most of the hemlock area this period is about 150 days. The cxjst of removal by this method is about $2.25 per 128 cubic feet (piled measure) of bark. The peeling cost is influenced by the loss of bark that occurs from the handling of the logs prior to arrival at the peeling deck. In one area where the bark on the timber ran normally three-tenths of a WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL I5 cord per thousand board feet, it was found that the quantity of bark being removed on the peehng deck was only two-tenths of a cord, indicating a handhng loss of 33^ percent. Similar losses were found at two other operations. At a fourth operation the loss was found to be practically doubled. The caufee was ascertained to be the high speed of skidding practiced by this operator. Not only was twice the amount of bark knocked off, but splintering and breakage were also excessive. The present tendency in the logging industry is toward less use of high-lead donkey-engine methods and more use of tractors and trucks. This more elastic and mobile logging equipment will un- doubtedly increase the opportunity for removal of bark at a reasonable cost and in a condition suitable for the production of tanning extract and will eventually add materially to the quantity of bark that may be classed as available. Deck-peeled bark is in general from logs that have been in either fresh or salt water. Consequently, with this type of bark both the leaching action of the water upon the tannin content of the bark and con- tamination of the bark with salt (sodium chloride) must be considered. Prolonged immersion of the bark in water has a pronounced leaching action upon the soluble matter present and lowers the tannin content, as shown by the analyses in table 6. The quantity of tannin lost in this way depends upon the length of time in water. The average percentage of seven samples of bark from logs passed through ponds in 2 to 12 days and peeled within 3 weeks after felling was as follows: Total solids, 26.4; soluble solids, 23.4; insolubles, 3.0; nontannins, 8.3; tannin, 15.1. By comparison with values already established for prime bark, these results indicate little loss of soluble matter and tannin from bark on logs handled through ponds with normal dispatch. For satisfactory bark, the upper limit from felling to peeling, including passage through ponds, may be tentatively set at 3 to 4 weeks. The effect of immersion of hemlock bark in salt water, including absorption of salt by the bark, has been shown by Templeton and Sherrard (15). Table 7 is a reproduction of their data.

TABLE 7.—Composilion of western hemlock hark after being in salt water 1 [Results on moisture-free basis] Num- ber of Solu- Insolu- Non- Tan- NaCl NaCl Series no. deter- Total ble bles tan- nm in in mma- solids solids nms bark ross tions Percent Percent Percent Percent Percent Percent Percent 1. Not in salt water 6 23.01 20.07 2.94 8.24 11. 82. 0.036 II. In salt water 30 days 8-6 26.84 24.45 2.39 8.37 16.16 .686 0.426 III. In salt water 60 days 6 25.36 21.66 3.70 8.67 12.99 2.56 IV. In salt water 90 days 5 29.02 24.89 4.13 8.51 16.38 1.53 i.63 iFrom Templeton and Sherrard (15).

The sodium chloride COD tent of the bark after immersion in salt water ranges from 0.69 to 2.56 percent. Salt, being readily soluble, would be removed with the tannin in making an extract from the bark. The amount of salt in the resulting dry.powdered extract would be approximately five times that in the bark. A high content of salt in tan liquors is considered objectionable by nearly all tanners of sole and other heavy vegetable leathers, in view of which bark from logs that have been in brackish or salt water should be considered for the present at least as not suitable for making tanning extract. 16 TECHNICAL BULLETIN HOC, U. S. DBPT. OF AGRICULTURE WOODS PEELING Woods peeling ordinarily produces ideal bark and is the general practice in collecting tanbarks in the eastern and southern sections of the United States. However, in many of the western henalock stands and operations, woods peeling is practically impossible. The average hemlock log cut for timber is about 26 inches in diameter and 35 feet long. Logs 48 inches in diameter and 72 feet long are not uncommon. Those less than 16 inches in diameter and 16 feet in length are not considered worth cutting for lumber. Because of their tremendous size the logs cannot be manually handled and consequently cannot be peeled without the help of machinery. In addition

FIGURE 3.—feeling (yl) and piling (H) tinrlv in the woods to cure. the heavy undergrowth, tops, and felled timber form a tangle, from which the logs are skidded to landings by various types of machinery. Under such conditions the impossibility of peeling in the woods, or even if this could be done, the subsequent removal of either the cured or uncured bark from the trackless wilds at a reasonable cost, can be readily appreciated. As a consequence the bark is carried out on the logs, and the bulk of it is later removed mechanically, as has already been described. There are, however, two types of operations where woods peeling is or might be done (fig. 3). One of these is the tractor and truck logging operation previously referred to. The other is the cutting of split pulpwood by relogging. The cost of removing bark in the woods exceeds the cost of removal on peeling decks, where the logs can be handled by machinery. One operator who kept extensive cost records on bark removal found that peeling bark from logs in WESTEKX HEMLOCK BARK A PUXKMIAL XA>M>U JIATEIUAL ^7 the woods costs at least $3.75 per 128 cubic feet (piled measure). This is SB 1.50 more per cord than deck peeling, even though each log carried one-third more bark in the woods than it did on reaching the peeling deck. The operation most favorable to the woods peeling of bark is the production of split pulpwood (fig. 4). The trees are felled and bucked into 48-inch lengths, and the bark is peeled or hacked off with the ax before the wood is split. This bark is used to make walks and skid roads, or is left to rot where it falls. A cord of this bark properly piled to cure cannot be said to cost more than the extra labor expended in piling, or $1 per 128 cubic feet, and due to the necessary con- struction of skid roads to bring out the wood the bark can also be brought out at low cost.

WOODS CURING To determine the feasibility of woods curing as applied to relogging operations, actual curing tests were made on three carloads of bark, which were used subsequently for extraction and production of extracts. Three distinct locations were selected. One was in Grays Harbor FlGUEE 4.- -Bark peeled, piled, and cured in the woods. County, Wash.; the (Hplit pulpwood operation.) second in Clallam County, Wash.; and the third in Polk and Lincoln Counties, Orsg. The following curing procedure was used at each operation; The bark, in about 4-1'oot lengths, was turned ross side out and either spread around or leaned against a peeled log until the free moisture on the ross had evaporated. In favorable drying weather this required only a few hours and was almost always accomplished within 24 hours. The next step was to pile the bark properly. An open site near the peeling operation was selected, with a slight upgrade in the direction of the prevailing winds. Three small logs or sticks about 4 inches in 3 21720°—37 •■! lg TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE diameter and 8 feet long were laid parallel to each other about 18 inches apart and across the slope of the site. The difference in level between the two outer sticks was at least 8 inches. The bark was always piled flesh side down across the sticks. The width of the pile was never more than 8 feet, and 6 feet was found to be better. Each successive layer of bark was piled shingle fashion and racked forward a little at the high edge as lumber is racked. The high edge of the pile was always away from the prevailing winds. Care was taken to keep the pile level and not over 4 feet in height. The bark was piled during May, June, and July. In all locations it cured satisfactorily without heating or development of black mold. The cured bark was flat and had a bright flesh. About 6 weeks or more were necessary to completely cure the bark. These experiments demonstrated that satisfactory woods curing of bark is possible, but only in certain rather restricted areas where logging operations are carried on under the most favorable conditions and the bark is handled by experienced or trained labor. Compara- tively speaking, bark handled in this way would form only a minor contribution to the total supply. The likelihood of poor piling by the cutting crews resulting in poor curing would add to the risk of getting out marketable bark. Furthermore, in most operations the wood is taken out within 2 to 3 weeks after being split and corded, but an additional 3 weeks or more would be required for curing the bark, during which time the bark would be exposed to a high fire risk with no workmen near to act as watchmen.

SEASONAL VARIATION IN TANNIN CONTENT Peeled bark, including both deck peeled and woods peeled, is a seasonal product. The influence of season of the year upon the tannin content of western hemlock bark (Tsuga heterophylla) is shown by the work of Clark and Andrews (8). Their analyses of bark taken at different times of the year from trees, either standing or just felled, from Kingcome Inlet, British Columbia, near the Kingcome River, are given in table 8. In no case had the logs been in water.

TABLE 8.—Seasonal variation in tannin content of western hemlock hark ^ [Results on moisture-free basis]

Nontan- Soluble Insolubles Tannin Date of collection Total solids solids nins

Percent Percent Percent Percent Percent 18.44 17.78 0.66 5.73 12.05 Feb 14 20.27 19.64 .63 6.98 13.66 Apr 12 -- 22.10 21.66 .45 6.82 14.84 May 15 --- -- 22.96 22.28 .68 6.78 15.50 June 15 - 22.30 21.70 .60 6.40 15.30 July 20 -- 20.50 19.16 1.34 5.01 14.15 Aug 15 - 15.98 15.48 .50 . 4.14 11.34 Sept. 15 14.88 14.51 .31 4.05 10.52 Nov. 15 12.96 12.89 .07 3.89 9.00 AvprniTP AnciT^t to Tanuarv 10.73 Avpraffp T'pbruarv to Julv 14.69 12. 93

1 From Clark and Andrews (8). The peeling season when these samples were taken was from Feb- ruary to July, inclusive. The average tannin content of the bark collected during this period was 14.69 percent, or 36.9 percent more than that of the bark taken during the rest of the year, when it woidd not peel. On the average therefore peeled bark will be appreciably WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL JQ richer in tannin than mechanically removed bark from year-round timber and consequently will give a higher yield of extract. From the foregoing discussion it can be deduced that at present the only bark suitable and available for extract manufacture is that from the production of split pulpwood and that removed on peeling decks, including bark from logs out of fresh-water ponds. On this basis it is estimated that under present operating conditions there are available annually at least 50,000 cords of bark at an actual cost of less than $5 per cord delivered to a nearby extract plant. Many of the present logging procedures can be modified to increase the volume of suitable bark from 100,000 to 150,000 cords yearly over that now available. It should be kept in mind that the utilization of pulpwood from hemlock sawlogs requires the removal of the bark, regardless of whether or not the bark is to be used. Any use that would even partially offset the cost of this operation should be an inducement to salvage and market the bark. ARTIFICIAL DRYING I'rom a study of the actual logging operations in the western hemlock belt it is evident that artificial drying of the bark must be employed. Hemlock bark, and nearly all tanbarks, must age for at least 4 months before being leached or extracted. Tan liquors from fresh hemlock bark will impart to leather an uneven color and mottled appearance. This has been repeatedly observed by tanners and was evident in these studies on experimental tanning with extract from fresh western hemlock bark. Storage of bark is necessary not only for the reason just given but also because the production of peeled bark is seasonal, whereas the operation of an extract plant is preferably continuous. As a general practice, each year's bark supply for the plant would have to^be collected and stored during approximately the 5 months of the peeling season of the previous year. For proper storage in bulk in sheds, as is customary, the moisture content of the bark at the time of storing must be not over 20 percent. Otherwise heating, fermentation, and molding will develop, with loss of tannin and serious discoloration of the extract made from the bark. Throughout this bulletin, moisture is expressed as true percentage and not added moisture, as it is customarily expressed for lumber. On a true percentage basis a bark containing 20 percent of moisture consists of 80 parts of dry material and 20 parts of water, whereas 20 percent on added moisture basis means 100 parts of dry material plus 20 parts of water. Twenty percent on an added moisture basis is equivalent to 16.66 percent of moisture on a true percentage basis. As has already been brought out, most of the bark at the available stage is quite wet. Green bark brought in directly from the woods has a high content of natural moisture, a maximum probably of 40 percent. Deck-peeled bark from log ponds contains more water, in extreme instances having a total moisture content of 60 percent, equivalent to 150 percent on the dry weight of the bark. Kapid artificial drying therefore becomes absolutely necessary in the salvage of the bark for extract production. It is consequently vital to determine not only the effect of the drying upon the tannin content of the bark but also whether or not artificial drying can be done at a feasible cost. For these reasons artificial drying of the bark has been ex- haustively studied. 20 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE EXPERIMENTAL TEST RUNS As the first drying experiment was only preliminary it will not be described in detail. Wet bark peeled from a log taken from the pond 72 hours after being dumped there was used in a small batch dryer. An attempt was made to approach conditions similar to those that would exist in a continuous dryer using a single or at most a double layer of bark on a continuous wire-screen apron, where the drying could be quickly accomplished. Several tests were run under conditions ranging from 5.5 to 23 hours heating at 140'' to 220° F. All tests yielded well-dried bark containing only from 7.2 to 10.4 percent of moisture. The four portions of bark subjected to the highest drying temperatures showed little, if any, loss of tannin. They contained 13.5, 13.7, 14.7, and 16.2 percent, respectively, of tannin, whereas the air-dried control bark for these tests contained 14.5 percent of tannin. These results were considered encouraging enough for further work. Due to shut-downs at the time, no dryers were available on the Pacific coast. However, through the courteous cooperation of the school of forestry of Oregon State College, an experimental drying kiln was made available at Corvallis, Oreg. Bark was obtained from a lumber company at Dallas, Oreg., about 30 mUes from Corvallis. The bark was peeled from such logs as happened to be in the pond each afternoon and was immediately transported to Corvallis, where it was sampled. Drying started before 11 o'clock the following morning. The logs had been in the pond for 12 to 48 hours, but some had been cut for as long as 6 weeks, dumped into the pond and hauled out and decked until needed, when they had again been put in the pond. The bark, therefore, was not equal in quality to an average run from this section. This was of secondary importance for these studies as each drying test had its individual air-dried control sample for comparison. The equipment at Corvallis consisted of a 22-foot section of a standard 11- by 12-foot dry kiln having a 20-ton scale for weighing while drying was in progress. Air was circulated in the kiln by three 12-blade disk fans, 38 inches in diameter, driven by motor with variable speed control. The kiln was provided with vents for ad- mission of fresh air and escape of moisture. It was heated by steam and provided with automatic control and recording of temperature and humidity.

TABLE 9.-—Drying experiments with western hemlock hark at Oregc m St 2te C ollege

Time Moisture in Tannin in bark i to Relative humidity bark Maxi- reach Time mum Run of maxi- Fan tem- mum Be- Air- Gain dry- speed After Kiln- per- tem- Maxi- Mini- fore dried or ing How controlled dry- con- dried ature per- mum mum drying loss ature ing trol

R.p. Per- Per- Per- Per- Per- Per- Per- Hours Hours m. cent cent cent cent cent cent cent -2.2 1 12.0 125 0.0 605 82.3 53.3 Maximum, 3 hours 40.4 20.0 14.2 12.0 r325- /Maximum, 5 hours }35.7 17.1 13.5 11.7 -1.8 2 8.5 170 1.5 1 490 } 71.8 54.7 \Minimum, 3 hours 3 4.5 219 4.5 605 48.5 30.1 Maximum, 3.5 hours.._ 48.3 18.0 13.2 11.7 -1.5 4 6.5 170 .5 490 45.7 38.9 44.0 17.0 11.8 10.7 -1.1 5 6.5 190 1.5 605 50.7 27.0 Maximum, 2 hours 50.8 14.3 13.0 12.0 -1.0 6 5.5 190 2.0 490 30.9 25.6 46.3 18.2 11.6 10.9 -.7 4.5 212 1.5 605 26.5 15.0 42.3 16.2 12.9 12.3 -.6 8 6.5 200 6.5 490 36.3 23.1 60.4 17.5 11.1 11.0 -.2 9 5.0 200 2.5 605 40.3 23.7 45.0 15.0 13.0 13.2 +. 1 10 4.5 212 3.5 490 29.3 22.3 44.8 17.8 15.0 15.6 +.6 1 On basis of moisture-free bark. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 21 Two methods of loading were tried. Tlie first method, used for runs 2 and 4 (table 9), was to stack the bark four layers high, each layer being separated by sticks 1 inch thick. The load was 8 feet wide and 20 feet long. In the second method, used for all other runs, the layers of bark were kept 2 inches apart by means of veneer racks and sticks, and the width of the load was reduced from 8 to 5 feet. In all cases the air now was across the load. Net-weight readings of the bark were made at K-hour intervals during the drying. At the end of the drying the truck was run outside, and the bark finally weighed the following morning after cooling overnight. In runs 1 and 2 (table 9), live steam was used to increase the humidity. In all other runs the humidity came from the moisture in the bark. Approximately one-half of each piece of bark was air-dried as a control; the other half was kiln-dried. The moisture content of the bark before drying and after drying was determined with samples dried for 24 hours in an electric oven at 102° C. The kiln record and the analyses of the air-dried control and its corresponding kiln- dried portion of bark for each run are shown in table 9. The test runs in table 9 are arranged in descending order of loss of tannin by the bark from artificial drying. Time of drying and humidity are evidently the important factors governing alteration of the tannin content of the dried bark. The greatest losses of tannin occur upon drying at high humidities, a sustained relative humidity of 40 percent or more causing marked reduction of the tannin content of the bark. The results of these experiments clearly establish that wet bark can be rapidly dried at temperatures as high as 200° to 212° F. with but slight loss of tannin, about 0.5 percent on the basis of the bark, or 4 percent of the tannin in the bark, provided the rate of air flow is sufficient to prevent a relative humidity of more than 40 percent in the dryer. Because of limited steam pressure, the maximum temperature that could be obtained in the kiln was 220° F. The results in table 9 strongly suggest that temperatures appreciably higher than 220° might be safely used in artificial dmng. The feasibility and cost of artificially drying bark was taken up with the engineers of two large producers of drying machinery. Both expressed the opinion that with the cheap fuel available from spent bark after extraction, augmented, if necessary, by ''hogged'' fuel at not over 75 cents per 200 cubic feet, a continuous dryer having sufficient capacity to handle the volume of fresh bark which would be delivered at any one extract plant during the peeling season could be designed to operate satisfactorily. It was estimated that every 24 hours the dryer would have to dry 100 tons of bark with an average moisture content of around 35 percent to a moisture content of about 20 percent.

TEST RUNS BY MANUFACTURERS In order to secure actual data on which to base estimates of cost of equipment and drying, test runs were conducted by each of the manufacturers. Special arrangements were made whereby small lots of bark peeled from trees at time of cutting and also wet bark from logs out of ponds were collected, packed in airtight containers, and immediately shipped east. Information on the length of time that 22 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE the logs had been in the ponds could not be obtained, but evidently it was a prolonged period as the samples of bark were heavily water- logged. All the samples arrived at their destination within 5 days after shipping and showed no evidence of molding, heating, or drying out. Each piece of bark was originally cut 20 by 25 inches and numbered. Five inches were cut off each piece as received, and these portions were air-dried for control samples for each run. It was thought that heat up to 300° F. could be used without damag- ing the bark. The bark was considered sufficiently dried when it became brittle and the flesh did not stick to the fingers when freshly broken. The air flow was upward through the bark in all tests except the first (table 10), in which a single piece of bark was used with the air impinging against both sides. The essential conditions for the drying tests together with figures on the tannin content of the bark are given in table 10. . Several methods of loading were tried. The best drying occurred with a single layer of bark with the pieces touching as httle as possible. To obtain capacity and uniform drying while keeping the size of the dryer as small as possible it was found that the bark would have to be loaded vertically with a density of not more than nine pieces to the foot of dryer. The data in table 10 show that when the bark is loaded in this manner satisfactory drying with a minimum destruction of tannin can be obtained within 2 to 3 hours at a temperature of 230° to 290° F. and with an air flow of at least 250 to 350 cubic feet per minute to insure within the dryer a sufficiently low humidity. From these tests one manufacturer estimated that a dryer operated by waste heat without steam coils to produce per hour a quantity of dried bark equivalent to 4 tons of bark of 15-percent moisture could be furnished and installed for $20,000 to $25,000 and operated on the following basis: Steam, 3,500 pounds per hour at 25 cents per M for 150 days, 24 hours per day * ' Labor," three 8-hour shifts, 3 men each shift, 150 days at 50 cents per hour _ 5, 400 Amortization, 10 years and interest 2, 300 Repairs per season ^^ Lubricants per season ^ Total 11> 100 This gives a cost of about 77 cents per ton of bark containing 15 percent moisture. The other manufacturer submitted preliminary figures givmg a cost of about 84 cents per ton of dried bark, and an initial cost of about $35,000 for equipment and installation to produce 5 tons of dried bark per hour. LARGE-SCALE DRYING TESTS Large-scale practical drying tests were then made at Portland, Oreg., with a dryer designed for usé in the manufacture of plywood. The machine was of the endless-belt type and when in motion carried the bark in single layers in opposite directions between wire screens. The dryer was heated by steam and equipped with circulating fans and recording thermometers, the bulbs of which were between the layers of bark. When loaded, the belts of the dryer were stopped for the drying period employed. The belts were then again started and unloaded and reloaded simultaneously until again full of undried bark, when the belt movement was stopped. TABLE 10.—Drying experiments with western hemlock hark at plants of dryer manufacturers

Temperature Water Tannin in bark 2 Time of Air flow driven Bark from logs Pieces drying per min- Heat source off on Condition of dried bark Above °F. ute wet-bark Control Dried Loss or bark basis 1 sample sample gain

Number Hours Inches Cubic feet Percent Percent Percent Percent Just felled _.. 1 0.25 6 305 600 Steam . 18 18.8 18.1 -0.7 Not dried sufficiently. Do - 5 1.00 6 280 300 do 15 16.8 16.8 -.0 Do. Out of pond 5 1.00 6 280 300 do 15 11.6 10.7 -.9 Do. o Just felled- 6 1.75 6 290 350 Gas 27 16.6 15.7 -.9 Too dry. Color dark. Do 6 2.00 6 290 600 Steam 27 16.8 16.2 -.6 Satisfactorily dried. Color bright. Out of pond 6 2.25 6 290 500 do 27 10.4 10.5 +.1 Do. Just felled _ 6 2.25 1 248 250 Gas 26. 5 14.2 14.7 +•5 Do. td Do 6 3.00 3 230 300 do 26.5 16.3 15.5 -.8 Satisfactorily dried. Partly discolored. Average _ 15.2 14.8 -.4

' Original moisture content of bark from logs just felled, 40 percent; from logs out of pond, 52.4 percent. 2 Expressed on moisture-free basis. O

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fcO 00 24 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE The air flow in the dryer was not over 150 to 200 cubic feet per minute. The humidity consequently was relatively high and cer- tainly above that which would prevail in a dryer properly designed for drying bark. On the whole the drying conditions were not nearly so ideal as those that gave the best results in previous tests, but the dryer was the nearest approach to the type desired that could be se- cured for this work. A full charge for the dryer consisted of 500 cubic feet and required 45 minutes for loading. In arranging for the use of the dryer, a tenta- • tive agreement was reached with the owner covering cost of labor, steam, and use of equipment. On the basis of this agreement and the foregoing capacity and allowing an actual drying period of 2.5 hours per load, the cost of drying per ton of dried bark was 85 cents. This figure is quite in harmony with those of 77 cents and 84 cents per ton of bark submitted by the manufacturers of drying machinery. Unfortunately the entire program for this work was seriously dis- arranged by a strike of the longshoremen, which caused a number of bark suppliers to suspend operations, interfered with means of transportation to the dryer, and finally resulted in the closing of the plant owning the dryer to be used. Consequently, special arrangements had to be made at a considerable advance in cost and with the sacrifice of all actual cost studies and preliminary work and curtailment of the schedule of tests that had been planned. The bark used came from a number of sources in Washington and Oregon. It was delivered in units of 200 cubic feet and represented a fairly true cross section of the available supply of bark. Every fourth piece of bark was air-dried at 60° to 85° F. for control samples. Every odd piece was artificially dried. As the dried bark was taken from the dryer it was closely piled on trucks and left for 24 to 48 hours before being sampled. The pertinent data from these tests are given in table 11. The average tannin content of the nine lots of control, or air-dried bark, in table 11 is 15.25 percent, which is in close agreement with the value of 15.5 percent of tannin previously established as a fair average. One of the objects of these tests was to learn how long green and wet bark could be closely piled, as would be necessary in transporting it from the source to the dryer, without heating, molding, and marked loss of tannin. From the results obtained it would appear that there is no serious deterioration up to 72 hours and possibly up to 96 hours. Under the conditions that prevailed in these experiments, drying at 260° to 280° F. for 2.5 hours produced bark of a sufíiciently low moisture content. Indeed, the evidence is that drying for 2 hours would have been enough. The average tannin content of the artificially dried bark is 13.44 percent as against 15.25 percent for the air-dried controls. This is an average loss of 1.81 percent on the basis of the bark, or of 11.87 percent of the tannin in the bark. In view of the findings of previous drying tests this comparatively high loss can be attributed to unfavor- able conditions in the dryer because of a low air flow and, consequently, a prevaiHng high humidity. This loss is nearly the same as that found in those drying experiments at Oregon State College (table 9) in which there was a prevailing relative humidity of 40 percent or more. On the other hand when the humidity was below 40 percent the loss in tannin was slightly less than 0.5 percent on the basis of the bark, or 3.5 percent of the tannin in the bark. TABLE 11- -Pilot-scale drying of western hemlock hark at Portland, Oreg.

History of bark Drying record Moisture in bark Tannin in bark i Bark piled Location of trees Elevation before Dried Logs put in drying Time of Temper- Before After Control Loss Trees felled water Logs peeled drying ature drying drying sample 2 sample

Feet Date Date. Date Hours Hours Percent Percent Percent Percent Percent 2,500 May 19 Not put in May 21-- _. 96 2.5 258 26.0 11.9 13.7 12.1 1.6 2,500 May 20 May 22 ._ 72 2.5 271 25.9 13.6 13.1 11.5 1.6 o 2,500 May 21 do May 23. 48 2.5 268 37.5 15.0 15.0 14.3 .7 a Wahkiakum County, Wash— 2,000 May 11 May 16 May 19 144 3.5 274 32.2 6.1 15.6 13.1 2.5 2,000 May 13.- May 18 May 21 96 3.5 274 46.3 10.1 15.6 13.3 2.3 2,000 May 16 May 21 May 22 and 23 72-48 1.25 260 47.3 23.4 16.2 15.6 .6 td 2.2 1,500 May 18 Not put in May 19 and 21.... 144-96 2.5 274 26.4 13.0 3 15.6 3 13.4 >■ Clackamas County, Oreg 1, 500 May 21 . . May 21 . 96 3.5 274 27.3 5.6 16.5 14.3 2.2 1,500 May 22 do—- May 22 72 3.5 270 29.1 8.3 16.0 13.4 2.6

1 Expressed on moisture-free basis. 2 All control samples dried in air in single layers for 96 hours at 60° to 85° F. O 3 Slight white mold formed with rise in temperature inside the pile.

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S! >M 26 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE

OPTIMUM CONDITIONS From the bark-drying studies it may be concluded that a continuous belt-type dryer operated at 250"^ to 280"^ F., with sufficient air flow to keep the relative humidity below 40 percent, will satisfactorily dry either green bark or bark peeled directly from logs out of water, in 2 to 3 hours at an operating cost of around 80 cents per ton of dried bark. The loss of tannin in bark dried in this manner should not exceed 5 percent of the tannin originally present. In any commercial project contemplating utilization of the bark as a source of tannin, artificial drying should be included as a necessary procedure unless the entire supply of bark is woods cured. EXTRACTION AND YIELD OF TANNIN The water-soluble portion of bark includes the active tanning agent. To remove this portion the ground bark is extracted with hot water either in open wooden vats, called leaches, or under pressure in closed copper autoclaves. The extraction in either case is called leaching. When in dilute form, the resulting solution is a tan liquor, but when concentrated to a sirup, soHd, or powder it is known as a tanning extract. The liquor or extract is composed of tannin, nontannins, and insolubles. The tannin is the portion that readily combines with the hide or skin in making leather. The nontannins and insolubles, however, are invariably associated with the tannin, and play an important part in the tanning behavior and characteristics of the extract as a whole. The important factors governing the completeness and efficiency of extraction are the grinding of the bark, the initial and final temperatures of extraction, the time of extraction, the pressure, and the ratio of water to bark. A number of extraction experiments covering a wide range of conditions were made. LARGE-SCALE TEST The first of these was a large-scale practical test made in CaHfornia at an extract plant operating normally on tanbark of the CaHfornia oak. The primary object of this work was to secure bulk lots of western hemlock-bark extracts for study of their properties and for large-scale tanning tests. In all, 80 tons of bark were used, comprising 57 tons from the previously described woods-curing experiments and 23 tons of deck-peeled kiln-dried bark from logs from a fresh-water pond. Because of lack of sufficient equipment and flexibility, a good yield was not possible. The xnill for grinding the bark was of the hammer type instead of the shaver or planer type, with a %-inch cage. At least 12 percent of the groiTnd bark was entirely too large, consisting of pieces up to % by 1% inches. Also in this type of mill the cellular structure of the bark is not broken down sufficiently. The lack of closed heating coils made it impossible to maintain the desired temperatures throughout the system without increasing the liquor volume and dilution excessively. Consequently, the liquors drawn off for evaporation were never over 125° F., and in most cases not over 110°. Furthermore, inadequate evaporating facilities extended the leaching cycle up to 10 days. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 27 Altogether 129,058 pounds of moisture-free bark were extracted, and 47,736 gallons of liquor of 14.8° barkometer were obtained. This Uquor was subsequently concentrated into about 7 tons of extracts of several types. The similarity of the western hemlock bark to the better known eastern species suggests that the same leaching procedure might be used for both. Conferences with tanners of many years of experience in leaching eastern hemlock bark developed the following essential points. Grinding to break down the cellular structure of the bark is essential. This mtist be done, however, without the production of a large proportion of dust and fine particles, or difliculty in percolation of the liquors through the leaches will be encountered. Mills with a shav- ing action have been found to be best. Leaching must be done at relatively high sustained temperatures and completed within 3 to 4 days. Under favorable conditions a leaching efficiency of 80 to S5 percent can be obtained.

LABORATORY RUNS In laboratory studies of leaching and yields, three types of grinding were used. That designated as coarse was the ground bark produced at the extract plant in California; the second, designated as analytical, was the coarse bark reground in a Wiley mill to pass a 3-mm screen; and the third, referred to as commercial, was obtained by sifting the coarse bark through a K-inch mesh screen and regrinding the portion that did not pass in a Wiley mill without a screen until all the pieces were sufficiently reduced in size to pass the %-inch screen. The last type, while not ideal or equal to a good commercial preparation made in a mill of the shaver principle, closely approximated a good commercial preparation made in a hammer and cage type of shredder such as is used by many tanners to grind eastern hemlock bark for leaching. The first four laboratory open leaching tests (2A to 2D, inclusive, table 12) were made in single leaches with closed heating coils. The bark was wet with water, and the desired temperature held until the liquor was drawn off. This was repeated for each draw-off, the leach being reffiled each time with water. For the last four tests, 3A to 3D, inclusive, four leaches, each with a capacity of 8 to 11 pounds of bark, were set up as a unit, with one connected to the other in series. Each leach was equipped with a false bottom, below which were a closed heating coil, an open steam jet, and a draw-off valve. The four leaches were so connected that the liquor could be moved by means of an air jet from the bottom of one to the top of the other. The bark in leach no. 1 was wet with water at a given temperature. This temperature was maintained for 2 hours, and the liquor was then drawn off. The leach was refilled with water at 185^ F. and kept at this temperature. Leach no. 2 was filled with liquor drawn through leach no. 1 after the first draw- off from the latter, allowed to stand for 2 hours, and then drained. Leaches nos. 3 and 4 were similarly handled. After the first draw-off, all liquors from each leach went on to the next leach. After each new leach had been wet, the tail leach was drained, refilled with water, and kept at 210° for 1 hour, then drained and cast, or emptied of spent bark. TABLE 12.—Open leaching of western hemlock hark 00

Leaching cycle Calculated to basis of moisture-free aew bark Yield of 95- Ratio of - percent tan- total Draw- liquor solids Test Grinding Total no. offs to dry New Tan- Spent Leaching ac- extract Initial temperature i Time bark by bark liquor bark eflQciency counted per 100 weight for pounds of bark 2

Percent Percent Percent Percent Percent Pounds Num- Total solids -- 29.1 14.4 8.1 49.5 77.3 79.8 ° F. Hours ber Soluble solids _ _ _ 25.8 13.6 7.0 52.7 5.6 3.4 60.2 96.8 [ 12.4 2A Coarse 140 for 21 hours 120 12 16.0 Nontannins-- -_ __.- 9.3 Tannin 16.5 8.0 3.6 48.5 70.3 .Purity 3 64.1 58.8 44.4 Total solids ------29.1 18.2 4.9 62.5 79.4 Soluble solids - - 25.8 16.5 4.4 64.0 81.0 2.5 71.0 97.8 [ 15.7 2B Analytical 140 for 21 hours 120 13 16.5 Nontannins - 9.3 6.6 Tannin 16.5 9.9 1.9 60.0 71.5 Purity 3 64.1 60.0 43.2 [Totalsolids.- - - 29.1 19.3 4.5 66.3 81.8 Soluble solids 25.8 18.2 4.2 70.5 86.8 8.5 2.3 91.4 116. 1 16.6 20 200 for 4 hours 96 12 15. 5 Nontannins — 9.3 Tannin. 16.5 9.7 1.9 58. 8 70.3 Purity 3 64.1 53.3 45.2 Total solids 29.1 24.7 3.4 84.9 96.6 Soluble solids 25.8 22.5 3.1 87.2 99.2 9.3 10.5 2.0 112.9 134.4 i 21.3 2D 96 11 18.4 Nontannins-- -- _-- - — Tannin _ - - 16.5 12.0 1.1 72.7 79.4 64.1 53.3 35.5 [Totalsolids --- - - 28.6 20.3 6.4 71.0 93.4 Soluble solids _.___- 25.1 19.0 6.0 75.7 99.6 8.6 6.7 3.6. 77.9 119.8 [ 17.8 3A Commercial 50 0) 14.5 " Nontannins- _ __- Tannin 16.5 12.3 2.4 74.5 89.1 Puritv 3 65.7 64.7 40.0 ÍTotal solids _ _. - 28.0 20.3 6.1 72.5 94.3 Soluble solids _ - - - - 24.3 18.9 5.6 77.8 100.8 7.1 3.1 78.0 112.1 i Í8.2 3B do 32 (*) 12.4 "{Nontannins- _. - -- 9.1 Tannin . _ _ _ 15.2 11.8 2.5 77.6 94.1 Purity 3 62.6 62.4 44.6 ÍTotal solids _ - . - 28.0 19.5 6.2 69.6 91.8 Soluble solids _ _ - - - 24.3 18.2 5.6 74.9 97.9 7.0 3.2 76.9 112.1 I 17.4 30 do 167 for 2 hours 30 14 14.3 ■{Nontannins-- 9.1 Tannin -- 15.2 11.2 2.4 73.7 89.5 lPurity3 62.6 61.5 42.8 Total solids-- 24.5 17.1 5.4 69.8 91.8 Soluble solids 21.4 16.1 5.1 75.2 99.1 176 for 2 hours.. 12 Nontannins— 8.1 6.2 3.1 76.5 114.8 17.5 Tannin 13.3 9.9 2.0 74.4 89.5 Purity 3 62.0 61.5 39.2

iFinal temperature always 210° F. . , ^„ „ .. . , ,.^ 3 Calculated on soluble solids. 2 Calculated from leaching efficiency on basis of new bark containing 15 percent moisture and 23.8.percent total solids. * Continuous.

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The first four tests show clearly the effect of a maximum range in the grinding or fineness of the bark. Over both ranges in temperature of extraction, the finely ground bark gave much greater yields. At the lower temperature, the yield for the finely ground bark represented an increase of 26.6 percent, and at the higher temperature an increase of 28.3 percent. This same group of extractions also indicates that an initial temperature of 200° F. is too high, even though the time of extraction is less than with an initial temperature of 140°, as the purity of the resulting tan liquor was lowered 6.1 points. The last four tests (3A to 3D) were conducted under simulated plant conditions using comparatively large quantities of bark prepared to correspond to commercial grinding and a set of leaches connected and operated as already described. Tests 3A and 3B involve two variables, namely, time and weight of Hquor to weight of bark. In the last two tests, 3C and 3D, a third variable is introduced by increasing the initial temperature of the liquor added to the dry bark. All four conditions represented by this group of tests (3A to 3D) gave essentially the same yields, ranging from 17.4 pounds to 18.2 pounds. An initial temperature of about 150° F. appears to produce a liquor of slightly higher purity. Leaching with a weight of liquor equal to 12 times the weight of the bark is evidently sufl3.cient.

OPTIMUM CONDITIONS From this work on open leaching it can be concluded that proper grinding of the bark is an important factor. The grinding should be fine enough to break down the cellular structure of the bark without producing, however, an appreciable proportion of fine dust. The initial temperature of the liquor run on the new bark should not be above 150° F. After the first draw-oft' of liquor the temperature of the leach should be raised rapidly to 200*° to 212° and maintained by means of closed heating coils. The total weight of liquor should be about 12 times the weight of the bark and should be passed through the bark in from 72 to 96 hours. The tau leach should be drawn down and drained at least 6 hours before casting and then refilled with water at 212° and maintained at this temperature until ready to cast. Yield is expressed as pounds of extract of 95-percent total solids per 100 pounds of bark. With a yield of 18, each 5.5 short tons of western hemlock bark of average quality and containing 15 percent moisture will produce 1 ton of powdered extract containing about 55 percent of tannin. A yield of 18 is obtained with a leaching efficiency of the total sohds of 71 to 72 percent. An efficiency of 80 percent in actual practice may be expected. This efficiency would give a yield of 20, according to which 5 short tons of the bark, instead of 5.5 tons, would produce 1 ton of powdered extract. If the weight of 1 cord of bark containing 15 percent moisture is taken as 2,300 pounds, the production of 1 ton of the powdered extract would require 4.8 cords for a yield of 18, and 4.35 cords for a yield of 20. EXTRACT PRODUCTION The tan liquors from either open or pressure leaching must be concentrated before marketing as otherwise transportation costs would be excessive. It naturally follows that extracts produced on the Pacific coast for marketing on the Atlantic coast must be concentrated WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 3I to the highest possible degree. To secure information on the cost of concentration, to study the influence of concentration on the character of the resulting extract, and to acquire suflicient material for subsequent commercial tanning, the liquors from the large-scale leaching done in California were made into several types of extract, including solid and powdered extracts. Leach liquors from bark ordinarily contain a relatively large quantity of insolubles. These fall into two broad classes. The first includes the insolubles readily removed by mechanical means. The second includes the insolubles that either cannot be removed mechanically without chemical assistance or that can best be taken care of by solubihzation. Removal of insolubles of the first class before concentration is highly desirable. The critical temperature that brought about the maximum elimination of insolubles of the first class from western hemlock-bark liquors was just below 100° F. Liquors cooled to this temperature and allowed to settle for 48 hours can be made into extracts that will compare favorably with extracts made from similar liquors not cooled but clarified by centrifugation at a rate considered practical. Centrifu- gation in this way removes about one-half the original insolubles and does not require a large expenditure of power, but it is doubtful if the result warrants the cost. If an automatic continuous-type machine of suflicient capacity to handle from 1,500 to 2,000 gallons per hour of tan Hquor of 1.04 speciflc gravity can be developed and operated so as to remove one-half the original insoluble content from uncooled liquors with the expenditure of not over 15 horsepower, then centrifugation may be practical, but until such a machine is available cooling and settling out should be used.

METHODS COMPARED Powdered extracts were made by two essentially different procedures. The first was the spray-drying method. Two desiccating machines of different design were used, and the liquor strength and method of atomization in each were varied until a satisfactory extract was produced. It was found that with centrifugal atomization the original liquor strength must be about 30 percent of total solids to produce a suflSciently dense powder, but when the pressure method of atomization was employed with a scrubber and preheater for waste- dust recovery, a 10-percent total-solids liquor could be used. However ■ with the equipment using the pressure method of atomization, the passage of the 10-percent total-soUds liquor through the preheater and scrubber raised its total solids content to over 25 percent at the ejecting nozzle. Consequently, with a scrubbing tower and the use of preheated Hquors for dust recovery either method of atomization would appear satisfactory. The powdered extracts produced all contained less than 5 percent moisture, and showed essentially no alteration in purity and color over the liquors from which they were concentrated. Drying costs by the spray-drying method have been calculated on the basis of starting with a 10-percent total-solids tan hquor and having 75 percent of the steam generated from spent bark from the plant plus suflicient hogged fuel at 75 cents per unit to supply the remainder. The calculations were made by one of the largest manufacturers of spray-drying equipment after a test run from which over 32 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE 5,000 pounds of powdered extract were produced. Under the conditions outlined, the cost of drying and bagging for shipment, including the cost of the bag, was not over 0.5 cent per pound of extract. In the second procedure for making powdered extract, tan liquor of 10-percent total-solids content was first concentrated to 45 percent of total solids in a multiple-effect vacuum evaporator. This 45-percent total-solids extract was then dried to a powder in a vacuum drum dryer. Using the cost factors for steam, power, operating, and depreciation of the plant where the extract was made, the manufacturer, after a series of test runs, calculated the cost of the finished extract, not including bags, to be 0.56 cent per pound. About 2 tons of solid extract was made by concentrating a 10- percent total-solids liquor to 50-percent soHds in a multiple-effect vacuum evaporator and then finishing in a single-effect pan under high vacuum. The cost of making this extract was less than that by either of the processes for making powdered extracts. Calculated on the same basic cost factors as before, the approximate cost was found to be 0.3 cent per pound.

PROPERTIES OF THE VARIOUS EXTRACTS The analyses of the original 10-percent total-solids liquor and the best extracts produced from this liquor by each of the methods of concentration are given in table 14 for direct comparison.

TABLE 14.—Analyses of western hemlock-hark liquor and extracts concentrated from the liquor

Purity on basis of— Mois- Total Sol- Insol- Non- Item ture solids uble ubles tannins Tannin solids Soluble Total solids solids

Percent Percent Percent Percent Percent Percent Original tan liquor 89.6 10.4 9.8 0.6 3.8 6.0 61.2 57.7 Powdered extract by spray drying... 5. 1 94.9 90.5 4.4 35.8 54.7 60.5 57.7 Powdered extract by vacuum drum drying 2.0 98.0 88.9 9.1 35.0 53.9 55.0 Solid extract by vacuum evaporation. 21.3 78.7 70.4 8.3 30.5 39.9 56.7 50.7

By comparison with the original liquor it will be seen that spray drying brought about practically no alteration in purity. The powder produced is easily soluble in cold water, and by the use of controlled heating and suitable agitators solutions containing as much as 50 percent of total solids can be readily made. The powder is but slightly hygroscopic, as shown by the following storage records. One lot of powder made in California in September 1932 was shipped to Phila- delphia, Pa., by water in paper-lined barrels of the kind used for flour, and stored. In barrels sampled 2 years later the powder showed no caking and contained only slightly more than 5 percent moisture. In April 1933 another lot of powder was made by spray drying in the Great Lakes area, from liquor shipped there from the Pacific coast in hardwood barrels. This powdered extract was packed in 100- pound lots in paper-lined sacks and stored for 1 year before being shipped to a tannery. Two sacks from this shipment were sent to Washington, D. C, and stored until October 1934, a total of 18 months. When sampled there was a thin surface crust that could be easily broken, and the maximum moisture content was 6.8 percent. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 33 The powdered extract made by vacuum drum drying was more crystalline than that from spray drying. The percentage of insolubles was materially greater, probably because of the longer exposure to heat, and the purity based on total solids was 2.7 points lower. The color imparted by this extract to cowhide skivers was darker than that from either the original liquor or from the spray-dried extracts. The solid extract shows the greatest alteration and lowering of purity. Of equal if not more importance, however, is its moisture content. This is over four times as great as that of a normal powdered extract. The freight on this additional quantity of water would amount to almost one-half the difference in manufacturing cost. Furthermore, an extract of this type must be seasoned for 2 to 4 months in dry warehouses to insure uniformity, thus adding to its cost. Storage experiments have also shown that this extract does not become crystalline under the prevailing conditions of temperature and humidity along the eastern seaboard, where the bulk of it must be consumed, but remains as an amorphous mass, difficult to remove from the paper bags. In addition, this extract would of course sell at a lower price, depending on its actual tanning content, shown in table 14 as 39.9 percent as against 54.7 and 53.9 percent for the powdered extracts. Photomicrographs of powdered extracts produced by spray drying and by vacuum drum drying are shown in plate 2. A very bulky powder made by direct centrifugal atomization of a liquor of 10- percent total solids is shown in plate 2, A. The color and solubility of this extract is excellent, but it is too bulky for economical commercial handling, having a weight of only about 22 to 24 pounds per cubic foot. Plate 2, By represents a powder made by use of pressure atomization of a liquor preheated and concentrated to 25 percent of total solids. It is a satisfactory density for shipping and handling, weighing about 40 to 42 pounds per cubic foot. This extract is not quite equal in color and solubility to the more bulky powder, but based on these two factors alone it would unquestionably rate as a high-grade extract. A powdered extract made by vacuum drum drying is shown in plate 2, (7. As compared with those of the other two powders, the great difference in size and shape of particles is quite evident and probably has a bearing on the darker color and lower solubility of this product. It is intermediate in density, weighing about 32 to 34 pounds per cubic foot.

RECOMMENDED PROCEDURE In summarizing these studies, spray drying is recommended as giving a superior product. Spray drying of leach liquors of about 10 percent of total solids direct from settling, clarifying, and mixing tanks, without the intermediate use of vacuum pans for partial concentration, is proposed. This procedure is a distinct departure from the customary processing of tanning extracts, but would appear from the experimental studies on extract drying to be feasible and desirable. As has already been pointed out, the liquors containing 10 percent of total solids upon entering the dryer are further concentrated by passage through the preheater and scrubber to between 25 and 30 percent of total solids before atomization. 34 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE The fact that spray drying is not in general use in the manufacture of tanning extracts should not be construed as establishing its unsuit- ability. While it is true that spray drying was tried and discarded by American extract producers, these trials took place nearly 20 years ago. At that time the superior quality of chestnut-wood extract made by spray drying was clearly recognized, but the fre- quent occurrence of dust explosions, the inability to control uniformity of production, and the higher cost of operation as compared with that of vacuum drum drying caused it to be abandoned. The higher cost was due in part to royalty charges exacted by holders of the basic patents of the spray-drying process. Few, if any, tanning-extract plants have been erected in the United States since the World War, but with the expiration of the basic patents on spray drying, engineers again turned their attention to the further development of this method because of its inherent advantages over other procedures, especially in the drying of delicate organic compounds where sustained heat is injurious. As a result, improvements in design have been made that reduce the possibility of dust ignitions and limit the damage by dust explosions. Develop- ments in methods of atomization have enabled manufacturers to secure powdered products of excellent uniformity. Finally, the introduction of preheaters and wet scrubbers for recovery of the waste dust, in place of the bag screens formerly used, has not only removed one of the primary causes of dust explosions, but has also increased the yield until there is practically no loss between the total- solids content of the solution being dried and that of the resulting finished product. In view of these facts, the conclusion that spray drying is well adapted for the production of tanning extract from western hemlock bark seems justified, provided due recognition is given to the design of the equipment and its installation to minimize or eliminate dust-explosion hazards. TANNING WITH BARK EXTRACT

LABORATORY EXPERIMENTS From the extraction and concentration studies, several tons of powdered and solid extracts of western hemlock bark were available. As a preliminary to large-scale practical tanning tests, a number of laboratory tanning experiments were made to study the character of the extract and its behavior when used alone or blended with other materials in tanning. Although on a small scale, the laboratory tanning was done under conditions and with equipment closely resembling actual tannery practices, especially with regard to rockers, vats, drums, extracting, bleaching, and finishing. A hydraulic press, however, was substituted for rolling. Pieces of a 60-pound country hide were tanned into sole leather using western hemlock-bark extract alone and with other extracts. The leather tanned entirely with the hemlock was medium reddish brown. It was firm but not harsh. The fiber pattern or w^ea^e, the fiber strength, and the thickness of the grain were excellent. But, judging by present commercial standards, the leather had an undesirable depth of color on both the grain and the fiber. No difticulties were experienced in blending the extract with equal quantities, respectively, of quebracho extract or chestnut extract. Sole leather tanned with a 50-50 blend of the hemlock extract and Technical Bulletin S66, U. S. Department oí Agriculture PLATE a

POWDERED EXTRACT OF WESTERN HEMLOCK BARK. A, Spray-dried extract made from liquor of lO-pereent total solids; weight per cubic foot, 22 to 24 pounds. B, Spray-dried extract made from liquor of 25-percent total solids; weight per cubic foot, 40 to 42 pounds. C, Drum-dried extract made from liquor of lO-perceut total solids; weight per cubic foot, 32 to 34 pounds. All X 75, WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 35 sulphited quebracho was not quite so firm or plump as that tanned with the hemlock extract alone, but was much fighter in color, being a light pink shade. When a similar blend was used with chestnut extract, a full and very firm leather was obtained having a light-brown color and a dark harsh fiber. On the whole the tanning action of western hemlock-bark extract was quite satisfactory. However, mixtures of this extract with other materials tanned light leathers more rapidly than did the hemlock extract alone. Preliminary experiments with pickled stock, such as calfskins, which require the addition of common salt to the liquors to prevent excessive sweUing, showed that salt did not adversely affect the solubility or color of the hemlock-bark extract. LARGE-SCALE TANNING TESTS For a practical evaluation of the extract, a number of large-scale commercial tanning tests were next arranged, emphasizing especially the use of the extract in making sole leather. Two such tests were made in cooperation with one of the largest tanners in this country. The first test was with 48-pound, October, branded, packer cowhides. The hides were put through the beamhouse and the rockers in the usual way. From the rockers, 376 sides, out of a total of 1,942 sides composing the entire lot, were put for 2 weeks into a special tan liquor containing western hemlock-bark extract. They were then drawn from this liquor and put into a second special liquor for 3 weeks. The rest of the sides in the lot received a similar treatment but in the regular tanning blend. After this aU sides were brought together again and received identical treatment throughout to the finished leather stage. The tan liquors regularly used at this tannery consisted of the following: blend, based on tannin content: ^ Percent Chestnut extract 42. 5 Quebracho extract 32. 5 Other extracts and tannin raw materials 25. 0 Total 100.0 For the special tan liquor, western hemlock-bark extract was added, giving a blend as follows, based on tannin content: Percent Western hemlock-bark extract 33. 3 Chestnut extract 28. 3 Quebracho 21. 7 Other extracts and tannin raw materials I"-' Total 100.0 It will be noted that the hemlock-bark extract was substituted to the extent of one-third of the entire blend. The sides that were tanned in the special hemlock blend were compared directly with regularly tanned sides. This comparison was made at a shoe factory where the entire lot was cut into soles. The factory reported as follows: We have examined and cut the leather on which one-third western hemlock bark extract was used. This leather was even in color and while a little redder or pmker than some tannages, the color was more pleasing. We think it has a more stable color which will not show up the usual factory and store dirt as quickly as most tannages. The most noticeable difference between this stock and the balance of 3ß TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE this lot was in the fiber and this was very pronounced. Our unanimous opinion is that the hemlock stock has more flexible firmness or bone and for our use is a little the most satisfactory stock for outsoles we have seen in years. This study was followed by a second test, in which 44 January, 55- pound , Colorado-steer hides were numbered so that, after splitting and tanning, the crops and bellies from the same hide could be identified. In addition all odd rights and even lefts of both crops and bellies were marked ^'A.'^ In tanning, the same procedure was followed as in the previous test. The stock marked ^^A^' was tanned in the layers to which western hemlock-bark extract had been added. After the layer tannage was completed, the crops and bellies from the 44 hides were reassembled and handled as a unit in each subsequent process until finished. This gave 44 crops and 44 bellies of the special hemlock tannage for direct comparison with the same number of the regular tannage from opposite sides of the same hides. The average weight and thickness of these leathers were as follows: Average weight of regular tannage pounds per side_ _ 16. 75 Average weight of hemlock tannage do 16. 72 Average thickness of regular tannage irons per side. _ 7. 07 Average thickness of hemlock tannage _do 7. 04 The tanner submitted the following comments: The hemlock stock color is slightly pinker with a slight advantage in uniformity and evenness of color, being better toned up. In general the hemlock stock has a little more ''guts", holds up better, and has better temper. Nineteen pairs of matched crops and 36 pairs of matched bellies of these two leathers were sent to a shoe factory for determination of their cutting value. The following report was received: We used the same dies, same cutters and same sorters, on both lots of crops and also on both lots of bellies, in order to have the comparison as accurate as possible. The hemlock leather was satisfactory in every way, the fiber being slightly tighter and firmer than the regular stock, and the color a little pinker. Considering the hemlock leather from all angles, we should say that we prefer this leather to the regular leather cut at the same time. These comparative tests showed a gain in cutting value by the special hemlock crops of 2.4 percent over the regular crops. Similarly the hemlock bellies showed an increase of 3.1 percent over the regular bellies. QUALITY AND ANALYSES OF HEMLOCK LEATHERS Actual wear tests of these two leathers were conducted with midshipmen of the United States Naval Academy and with civilians. Each pair of soles was cut from exactly corresponding locations in opposite sides of the same hide. One sole of each pair was cut from the regular tannage and the other from the hemlock tannage. In 55 completed tests, soles from the regular tannage wore through first in 26 cases. Those from the hemlock tannage wore through first in 15 instances, and in 14 instances the two soles wore through essentially at the same time. Based on hours wear per one-thousandth of an inch of leather worn away, the grand average of all the tests showed 7 percent greater wear for the hemlock leather. In cooperation with a light-leather tanner, three test packs of sheep- skins were put through. For the first pack, western hemlock-bark extract alone was used ; for the second pack, equal parts of the hemlock- bark extract and sulphited quebracho extract; and for the third pack, the same blend plus 20 percent of a synthetic tanning preparation. In the opinion of the tanner all the leathers were satisfactory. The straight hemlock tannage, however, was deep pink and therefore was WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 37 considered undesirable except for finishing in the dark shades. The feel of this leather also was considered harsher than is desirable. The leather tanned with the blend of hemlock and quebracho was much lighter in color than that tanned with the straight hemlock. Its color compared favorably with stock tanned entirely with sulphited quebracho, and its feel was considered satisfactory. The addition of the synthetic tanning material to the blend produced a leather of satisfactory feel, but its color while fair was not so good as when this material was omitted. . The chemical analyses of the various leathers tanned m the laboratory and commercially as just outlined are assembled in table 15. A number of pertinent conclusions regarding the character of western hemlock-bark extract can be drawn from the tanning work. The extract has a high combining value, producing a firm, plunap leather with a tight fiber. The color imparted to leather by the extract ranges from deep pink on light stock to brownish red on heavy sole leather. Both usable and salable light and heavy leathers can be made entirely from the extract, which would be important if a national emergency should make us entirely dependent upon domestic materials. The extract blends readily with the important tanning materials now in use. When mixed in blends up to 50 percent it does not materially alter the speed of tannage or the weight and plumpness of the resulting leather, and it imparts a desirable slight pinkness to the color of the leather. In mixtures it also produces a leather of a noticeably firmer and tighter fiber, making it a preferred material for tanning stock in which accentuation of these properties is desired. In carefully controlled experiments on the commercial tanning of sole leather the substitution in the usual blend of western hemlock- bark extract to the extent of 33)^ percent in the lay-aways slightly enhanced the putting value of both the outsole and insole leather produced, improved the appearance and feel of the finished leather, increased its ability to withstand wetting and redrying without loss of solidity and pliabiUty, and added slightly to its wearing quality as compared directly with regularly tanned stock from opposite sides of the same hides. ADEQUATE INITIAL PRODUCTION NECESSARY FOR SUCCESSFUL UTILIZATION, INTRODUCTION, AND MARKETING Sole leather tanners constitute by far the most important consumers of vegetable-tanning materials. This group uses over 75 percent of both the raw tannin materials and extracts that together make up our annual requirements. The tendency of all vegetable tanners to do away with leach houses and to purchase a larger proportion of ready- made extracts has been very marked since the World War. In 1931 over 70 percent of the vegetable tannin consumed in the United States was in the form of tanning extracts. Since the sole-leather tanner is the principal prospective buyer, consideration of his purchasing policy is essential. The first fact of importance is that the tanner does not confine his purchases to any one tanning material, but usually buys from five to eight different materials, depending on the character of sole leather he produces. His purchases comprise raw materials and extracts that yield roughly equal quantities' of the pyrogallol and catechol tannins, as blends of this composition have been found most suitable for the production of satisfactory sole leather. TABLE 15.—Analysis of leathers tanned entirely or in part with western hemlock-hark extract 00

Tannage Petro- Acidity Hide Water Uncom- Com- Mois- Total leum Non- Glu- MgSOi H No. Leather sub- solu- bined bined 1 of tan- fei Pro- ture ash ether tannins cose 7H2O Material extract stance bles tannin Procter- tannin nage O portion Searie PH

Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent O 48091 Sole. Hemlock... 100 11. 9 0.4 3.5 39.0 18.3 7.2 11.0 3.2 1.1 0.4 3.4 27.1 fHemlock... 50 48092 _do.. I 11.6 16.6 1.2 3.4 IQuebracho- 50 10.0 27.8 w -do- ÍHemlock... 50 \Chestnut..- 50 j- 12.3 .6 1.8 37.9 18.8 6.5 12.3 2.4 1.1 .3 3.3 29.0 76.5 d 48184 Calfskin.. Hemlock... 100 8.3 .6 3.8 53.1 6.7 2.9 3.8 .3 Trace .5 3.9 27.9 52,5 48094 do—. fHemlock-.. 50 iQuebracho- 50 !■ 12.7 .5 1.8 53.7 4.6 2.4 2.2 .3 Trace 1.0 3.7 27.0 50.3 {Hemlock... 50 48095 _do.. Quebracho. 50 10.9 .3 58.2 4.5 2.2 Trace 1.7 25.4 43.6 Syntan 10 48005 Sheepskin, unfinished. Hemlock... 100 2.2 2.0 46.5 5.9 3.9 Trace 1.3 2.7 31.7 68.2 48006 do ("Hemlock... 50 C55 IQuebracho. 50 9.8 2.7 2.6 44.2 7.9 7.1 Trace 1.2 2.7 28.1 63.6 JHemlock-.. 50 48007 .do-

i Insoluble ash assumed as 0.2 percent. O

d fel WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 39 The proper blend of materials is of the utmost importance to the tanner, and when it is once determined, reasons for modification must be clearly demonstrated. As the tanning liquors are reused until spent or practically exhausted, not only the immediate effect of a new constituent introduced into the blend must be considered but also its cumulative effect from reuse. Consequently, before a tanner can be per- suaded to use a new extract he must be convinced of its probable merit and will insist on a trial covering at least two tanning cycles. In the average sole-leather plant this will require from 50 to 500 tons of extract, depending on the thoroughness with which the trials are conducted. In addition to believing that the new material will prove beneficial to the tannage, the tanner must be convinced that the cost factor is favorable. Assurance must be given that use of the new extract will not increase the cost, at least by not more than the value it will add to the product. Furthermore, sufficient productive capacity and financial stability must be shown by the extract manufacturer to insure adequate future supplies at competitive prices. A plant producing annually 2,000 tons of powdered extract is considered the smallest practical unit that can be operated to meet the requirements essential to successful utilization of the bark and introduction and^marketing of its extract. A plant of this size, while not the most economical production unit, can be built to operate efficiently and at the same time be capable of expansion to double its capacity without doubling the plant investment. A plant producing about 4,000 tons of powdered tanning extract will consume around 22,000 tons of bark, which is probably the maximum quantity that can be readily assembled annually at any one location. To produce 2,000 tons of powdered tanning extract from western hemlock bark the following equipment is tentatively indicated. 1 unloading shed, 30 feet wide by 100 feet long, with 20-foot clearance. _ $2, 500 1 bark dryer 22,500 3 bark-storage sheds, each 50 feet wide by 350 feet long, with 30-foot clearance and a type A truss roof 10, 000 3 conveyors, including motors, for carrying bark from dryer to storage sheds, from storage sheds to grinder, and spent bark from leach house to furnace 7, 000 2 grinding units with conveyor fan, knife-sharpening equipment, and motors ----- 4,000 1 leach house equipped with 10 redwood leaches, 15 by 15 feet, clarifying and mixing tanks, and other auxiliary equipment 18, 000 1 desiccating house and equipment, including st.orage space for 200 tons of finished extract 50,000 1 power house, 50 feet wide by 70 feet long, with 30-foot clearance, and equipped with two 350-horsepower water tube boilers in dutch-oven settings and one 500-horsepower turboelectric generating set, with space sufficient for an additional boiler unit 20, 000 1 office, chemical laboratory, and equipment 6, 000 Equipment and items not specified 10, 000 Total '-- 150, 000 A site approximately 900 by 600 feet would be required for the assembly of this equipment into a plant with room for subsequent expansion to about twice the original capacity. The ground should be practically level and should be near a sufficiently large fresh-water stream to provide barge transportation for bark and hogged fuel as well as water for the plant. Access by rail and truck is also essential 40 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE A suggested plant lay-out is diagrammatically shown in figure 5. Expansion from an annual capacity of 2,000 to 4,000 tons of powdered extract is indicated by broken lines.

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FIGURE 5.—Plan of extract plant: a, Unloading shed; 6, bark dryer; c, conveyors; d, bark-storage sheds; e, bark-grinding outfit;/, leach house; g, desiccating house; h, power house; /, office;^, chemical laboratories; A, railroad sidings. CAPITAL REQUIREMENT AND OPERATING COSTS To the cost of buildings and equipment, which for a plant with an annual capacity of 2,000 tons of powdered extract has been estimated at $150,000, there must be added the cost of the plant site, which should not exceed $5,000, making a total plant investment of about $155,000. Operating capital must be large enough to cover plant investment; a bark supply sufficient for 1 year's consumption; manufacturing costs of a quantity of extract equal to stock-carrying requirements; transportation charges on shipments from the plant to the Atlantic port of sale; introduction and selling costs; and plant overhead. The following cost items are based on the findings presented in the text, together with experience in plant equipping and operation in the making of tanning extracts, and estimates by equipment manufacturers. Raw material has been figured from the yield studies on the basis that 5.5 short tons of bark of 15-percent moisture give 1 ton of powdered extract of 95-percent total solids. To the cost of the bark itself, which will be set forth later, s there must be added per ton of final dried bark 80 cents for drying and an equal amount for stacking and storing. In calculating fuel and power requirements it has been estimated that one-fourth of the fuel will be provided by hogged fuel at 60 cents per unit of 200 cubic feet, the remainder to be derived from the spent bark after extraction. Electricity has been figured at 1 cent per kilowatt. Labor requirements are shown in table 16. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 4^

TABLE 16.—Estimated labor requirements for operation of extract plant

Job Men Time Number General management_ 1 Yearly. Supervision 2 Do. Technical control _ -- 2 Do. OfiBce operation __. _ - 3 Do. Power production. _ 7 8 hours per day each, yearly. Drying bark.. -.- 6 8 hours per day each for 130 days per year. Stacking bark - _ - 20 8 hours per day each for 150 days per year. Conveying bark to grinder 4 8 hours per day each for 312 days per year. Grinding bark .__ 3 Do. Leach-house operation.- 3 Do. Concentrating and packing extract 9 Do. Shipping... -_- 5 8 hours per day each for 100 days per year.

Common labor has been figured at from 30 to 50 cents per hour, depending on the nature of the work. The necessary leaching equipment has been figured as 10 open wooden leaches, each 15 feet in diameter and 15 feet deep, arranged in battery formation. The spray-drying or desiccating plant has been calculated on the basis of continuous operation for 6 days per week, with stoppage equivalent to 1 day each week for cleaning and minor repairs. Its production capacity is estimated at 600 pounds of powdered extract per hour, or a maximum total yearly production of 2,246 tons. Transportation of the extract from plants located along the Pacific coast to the leather industry located in the East is a major item. Shipment by water via the Panama Canal to eastern ports should cost not more than $10 per ton, c. i. f. This is based on information obtained from steamship operators and not on existing rates, which are approximately double this figure. In the early stages of this study, the rate-making body, through which all steamship companies engaged in intercoastal freight service formally worked, quoted a tentative rate of 35 cents per 100 pounds as a reasonable figure on shipments anaount- ing to 1,000 tons or more per year. No definite contract establishing the rate can be obtained until actual tonnage can be oft'ered. In any proposed commercial development it is highly important, if not vital, that the establishment of a favorable freight rate receive early consideration and settlement. The final item is introduction and marketing. During the introductory period of a new extract, the marketing costs will unquestionably be high. For this reason, $5 per ton has been allowed for marketing. The foregoing items, exclusive of the cost of the bark, are sum- marized as follows: Per ton of powdered extract Drying bark, 5.5 tons at 80 cents per ton $4. 40 Stacking and storing bark, 5.5 tons at 80 cents per ton 4. 40 Grinding, leaching, and clarifying 9. 00 Desiccating, including bags and bagging 10. 00 Power, heat, and electricity not included above 1. 00 Transportation 10. 00 Marketing • 5. 00 Overhead, including supervision, taxes, and insurance 5. 00 Total . 48.80 42 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE PROBABLE SELLING PRICE OF EXTRACT The extract would be used by tanners in the United States to supplement the present blends, which are composed of tannins from both domestic and foreign sources. The tannin in western hemlock bark is of the catechol type. Since the most important domestic tannin is a pyrogallol one, it is logical to assume that the tanning materials most likely to be displaced by the hemlock extract would be those of the catechol classification derived largely from foreign sources. The market for the extract would not be confined exclusively to sole-leather tanners or to the United States. Canadian tanners import at least 75 percent of their requirements and are familiar with eastern hemlock bark. English tanners import almost all their requirements. European and oriental markets are also available, although due to domestic production some of them have tariffs that must be considered. The extract must be offered at prices competitive with those of established and available tanning material's. The average cost of domestic and imported tanning materials may be put conservatively at about 8 cents per tannin unit. The tannin unit is 1 pound of actual tannin, that is, the price quoted per pound for an extract containing 25 percent of tannin would be multiplied by 4 to get the price per tannin unit, or per pound of tannin. As has been brought out, the powdered hemlock-bark extract will contain about 55 percent of tannin. At 8 cents a tannin unit, an extract containing 55 percent of tannin has a selling price of $88 per ton. Assuming that the total cost per ton of the extract laid down at eastern ports, including an allowance of $5 for marketing, is 85 percent of the above selling price, the cost figure is $74.80. Costs exclusive of the bark have already been estimated at $48.80 per ton of extract. This would allow $26 for the bark, which at the rate of 5.5 tons of bark per ton of extract would give $4.73 per ton for bark. Assuming 1 cord of bark of 15-percent moisture to weigh 2,300 pounds, this figure would be equivalent to $5.44 per cord for bark that requires artificial drying. On the same basis, bark properly woods cured or naturally cured would be worth nearly $1 more per cord, or $6.44, because of elimination of need of artificial drying and also a slightly better quality and yield of extract. Tannins derived from barks, such as those of the chestnut oak and eastern hemlock, as distinct from tannins derived from woods, are usually recognized as preferred materials and bring better-than-average prices. In view of the excellent tanning properties displayed by western hemlock-bark extract, including its ability to blend readily with other materials and the desirable character of fiber it imparts, especially to sole leather, its classification among the preferred matei- rials at a price above the average is a reasonable expectation. The top price possible for western hemlock-bark extract cannot be determined at present. It obviously must not be so high that it do(3s not come within a competitive price range. On the other hand it must be high enough to permit a profitable and reasonably attractive price for the bark. It is doubtful whether the previously mentioned figure of $5.44 per cord for the bark, based on 8 cents a tannin unit, meets the latter requirement, although at many operations it would more than offset the cost of the removal of bark, which is necessary in using the log regardless of any use for the bark. WKSTEÎIN HEMtOCK RARÍv A POTRNT^TAL TANNING MATERIAL 43 On the basis of 10 cents per tannin unit the seUing price of the extract would be $110 per ton. Eighty-five percent of this amount, which represents the total cost per ton of the extract, is $93.50. On the same basis as previously presented, this cost figure would allow $44.70 for the bark, which in turn is equivalent to $8.13 per ton, or $9.35 per cord for bark. There is little doubt that prices of this order for the bark would prove quite attractive. On the other hand, it , would seem equally assured that a price of 10 cents per tannin unit would meet with strong sales resistance, at least during the introductory stages. For arriving at an estimate of capital requirements, a price for bark delivered at the plant has been taken as $6.50 per ton, which is an approximate average of the figures derived for bark on the bases, respectively, of 8 and 10 cents per tannin unit. On the cord basis of 2,300 pounds, this figure becomes $7.47. The capital requirement for a plant of 2,000 tons annual capacity, with provisions for subsequent doubling of capacity, is estimated as follows: Plant building and equipment $150, 000 Plant site 5, 000 Annual bark si:^ply, 11,000 tons at $6.50 per ton 71, 500 Drying and storing bark, 11,000 tons at $1.60 per ton 17, 600 Extract in process and held as stock, 400 tons at $48.80 per ton 19, 520 Contingent reserve . 16, 380 Total 280,000 SUMMARY The leather industry of the United States consumes annually about 115,000 tons of tannin, equivalent to 460,000 tons of 25-percent tannin extract. On the basis that the United States uses about half the world^s production of tannin, there is a potential annual world market for 900,000 tons, or more, of 25-percent tannin extract. The United States imports practically half the tannin it consumes annually. Two-thirds of its total consumption comes from two materials alone, namely, chestnut wood and quebracho wood. The domestic supply of tannin is derived chiefly from three sources. The major domestic source from which we now derive one-third of our total supply of tannin is being destroyed by the chestnut blight. ^ Tannins are used to make vegetable-tanned leathers, especially heavy leathers, such as sole, belting, harness, case, bag, and strap. It is estimated that the average annual production of vegetable-tanned leather in this country is around 425,000,000 pounds, of which about 82 percent is sole leather and other heavy leathers. There is growing within the continental area over 200,000,000,000 board feet of western hemlock. About each 5,000 board feet carry 1 cord of bark, which on the moisture-free basis contains over 15 percent of tannin. Tremendous quantities of this bark occur each year as an offal of lumbering and pulp production. In Oregon and Washington alone, over 400,000 cords are cut annually. ^ However, most of it is not now available in a form suitable for making tanning extracts. Bark mechanically removed as described is not suitable for recovery of tannin, primarily because of the presence of a high proportion of hemlock wood containing very little tannin. Since about three- 44 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE fourths of the bark is now removed in this manner, modification of present handhng to provide for removal in a usable form is important. Deck-peeled bark, including bark from logs out of fresh-water ponds, may be used, provided the logs are handled through the ponds with normal dispatch and are not in water preferably over 7 days. Such bark must be promptly dried and should average not less than 14.5 percent of tannin. Bark from logs out of salt water is not suitable because of con- tamination with sodium chloride, which would be concentrated in the extract made from the bark. The ideal bark is that peeled and properly cured in the woods. There are two types of operations in which the bark may sometimes be peeled in the woods. These are tractor and truck logging and relogging for split pulp wood. Under the most favorable conditions and with experienced or trained labor, the bark can be satisfactorily cured in the woods. Comparatively speaking, however, bark handled in this way would be only a minor contribution to the total supply. Peeled bark, including both deck peeled and woods peeled, is a seasonal product. During the peeling season the bark is richest in tannin and gives the highest yield of extract. Peeled bark is consequently to be preferred over bark removed from year-roynd timber. It is estimated that, with present operations, in Oregon and Wash- ington there are available annually for making into tanning extract at least 50,000 tons of western hemlock bark at a delivered cost of not over $5 per ton of bark containing 15 percent of moisture. The available supply probably could be increased to 150,000 to 200,000 tons by modification of logging practices that at present preclude peeling of the bark in usable form. Both woods-peeled and deck-peeled bark must be dried to a moisture content of not over 20 percent before it can be stored in bulk without deterioration. With the former this may be done by either natural or artificial drying. Wet bark from logs out of water must be promptly dried by artificial means. Artificial drying may be done in 2 to 3 hours at 250° to 280°F., provided the air flow in the dryer is sufläcient to keep the relative humidity below 40 percent. The loss of tannin in bark dried in this manner should not exceed 5 percent of the tannin present. The cost of drying is about 80 cents per ton of dried bark. Any contemplated commercial project to salvage this bark as tanning extract should definitely include artificial drying as a necessary procedure, unless the supply of bark is woods cured. The optimum conditions for open leaching of the bark are an initial temperature not above 150° F., followed by a rapid rise to 200° to 212°, which temperature is maintained. If properly extracted, 100 pounds of average bark with 15 percent of moisture will yield at least 18 pounds of powdered extract containing 95 percent of total solids and about 55 percent of tannin. Powdered extract produced by spray drying is recommended as giving a superior product. The cost of spray drying and bagging this type of extract for shipment is estimated at not over 0.5 cent per pound. The cost of drying powdered extract by vacuum drum drying is estimated at 0.56 cent per pound. Solid extract may be dried for about 0.3 cent per pound. This type of extract, however, is definitely not desirable because of its high WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 45 moisture content and alteration of the tan liquor during evaporation. Because of the long haul from producing plants near the Pacific coast to the consuming markets in the East, a product of maximum total solids content and minimum moisture content is absolutely essential. Powdered western hemlock-bark extract is practically nonhygro- scopic in the trade sense of the word. In moisture-proof paper-lined containers it may be shipped by ocean freight or stored for long periods in humid regions without becoming caked or difficult to handle and redissolve. It has been demonstrated that western hemlock-bark extract can be used alone to produce marketable commercial leathers. Leather tanned with this material alone is firm but not harsh. Its fiber weave and fiber strength are excellent, but judged by present commercial standards the color is undesirably deep. The extract blends readily with the usual tanning materials. When mixed in blends up to 50 percent it does not materially alter the speed of tannmg but produces a leather of a noticeably firmer and tighter fiber. Carefully controlled sole-leather tanning tests were made comparing the regular leather with leather made by substituting western hemlock- bark extract to the extent of 33K percent in the lay-aways. The leather made from the hemlock mixture was even in color and while a little redder or pinker than some tannages the color was more pleasing. The most noticeable difference was in the fiber. The hemlock leather had more flexible firmness or ''bone'' and was a satisfactory stock for outsoles. In other similar tanning studies, the substitution of the hemlock extract to the extent of one-third of the blend slightly enhanced the cutting value of both the outsole and insole leathers produced, improved the appearance and feel of the finished leather, and increased its abiUty to withstand wetting and redrying without loss of sohdity and phability. Wear tests with midshipmen of the United States Naval Academy and with civilians showed that it added about 7 percent to the wear of the leather as compared with regularly tanned stock made from opposite sides of the same hides. The smallest practical extract plant should have an annual capacity of 2,000 tons of powdered extract, and be so designed as to be capable of expansion to twice this capacity without doubling the plant investment. A plant producing 4,000 tons of extract will consume about 22,000 tons of bark, which is probably the maximum quantity that can be readily assembled yearly at any one location. Because of the distance involved, the cost of transporting the extract from the Pacific coast to the East is a vital factor. In any proposed commercial development, early consideration and fixing of a favorable freight rate is of utmost importance. The cost of producing powdered western hemlock-bark extract, including drying and storing the bark, processmg, transportation, and marketing, but exclusive of the cost of the bark, is estimated at $48.80 per ton. Capital requirement, including site, buildings, equipment, a year s supply of dried and stored bark, and a stock of extract equal to 20 percent of the annual production, is estimated at $280,000 for a plant producing 2,000 tons of extract yearly. On the basis of an average value of 8 cents a tannin unit and a tannin content of 55 percent, a selling price of $88 per ton of extract is obtained. It is estimated that this selling price would permit 46 TECHNICAL BULLETIN 566, U. S. DEPT. OF AGRICULTURE only about $4.73 per ton, or $5.44 per cord, for bark of 15-percent moisture content. At many operations this price would more than offset the cost of the necessary removal of the bark. Whether it is sufficiently attractive to encourage proper salvage of the bark is doubtful. That the extract may find its place among the preferred materials and eventually bring a higher seUing price is a reasonable expectation. Domestic-bark tannins from chestnut oak bark and eastern hemlock bark are recognized as preferred materials. The top selling price for powdered western hemlock-bark extract cannot be determined at present. At 10 cents per tannin unit the selling price of the extract would be $110 per ton. It is estimated that this price would allow about $8.13 per ton, or $9.35 per cord, for the bark. Prices for bark in this range it is beheved would prove quite attractive, but on the other hand 10 cents per tannin unit will meet with strong sales resistance. Development of the hemlock bark of the Pacific coast region as an important source of tanning extracts can succeed only if undertaken with sound financial backing adequate to survive a comparatively costly introductory period of several years. This must be coupled with experienced management and rigid chemical control to secure maximum yields of a uniform product. Production must be on a scale large enough to insure the tanner adequate future suppHes at reasonably competitive prices. This must be supplemented by a sales force thoroughly acquainted with the leather industry and the technology of tanning. Successful utilization of the bark hinges on a rather narrow working margin of profit. A careful balance must be struck whereby sufficiently attractive prices can be offered for the bark without, however, imposing upon the extract a selling price that is prohibitive. Quick returns and large profits are not to be expected. On the other hand, in view of the tremendous quantities of bark and our large annual consumption of tannin in the making of a basic national commodity, namely, leather, there appears to be an opportunity of establishing a permanent business of large volume. Successful salvage of the bark as tanning extracts would increase our taxable wealth by adding value to a product that is now not used, give employment to domestic labor, decrease our dependence upon foreign materials, thereby adding to our national security in an emergency, and increase our exportations in normal times.

LITERATURE CITED (1) ANONYMOUS. 1893. HEMLOCK BARK AT THE FAIR. Hide aiid Leather 5 (25): 37. (World's Fair Supplement). (2) ~ 1926. TANNIN FROM WESTERN HEMLOCK. Timberman 27 (11): 178, 180 (3) ALLEN, E. J. V y , . 1902. THE WESTERN HEMLOCK. U. S. Dept. Agr., Bur. Forestry Bull. 33, 55 pp., illus. (4) AMERICAN LEATHER CHEMISTS ASSOCIATION. 1930. BY-LAWS AND METHODS OF SAMPLING AND ANALYSIS, 120 pp., illus. (5) BENSON, H. K., and THOMPSON, T. G. 1915. THE TANNIN CONTENT OF PACIFIC COAST CONIFERS. Jour. Indus and Engin. Chem. 7: 915-916, illus. (6) — THOMPSON, T. G., and WILSON, G. S. 1923. THE CHEMICAL UTILIZATION OF WOOD IN WASHINGTON. Wash [State] Engin. Expt. Sta. Bull. 19, 160 pp., illus. WESTERN HEMLOCK BARK A POTENTIAL TANNING MATERIAL 47

(7) CANADA, DEPARTMENT OF INTERIOR. 1924. WESTERN HEMLOCK. Canada Dept. Int., Forestry Brancli, Tree Pamphlet 5, 7 pp., illus. (8) CLARK, R. H., and ANDREWS, H. I. 1921. THE TANNIN CONTENT OF PACIFIC COAST CONIFERS. Jour. InduS. aild Engin. Chem. 13: 1026-1027, illus. (9) Goss, O. P. M. 1913. MECHANICAL PROPERTIES OF WESTERN HEMLOCK. U. S. Dept. Agr., Forest Serv. Bull. 115, 45 pp., illus. (10) HANZLIK, E. J., and OAKLEAF, H. B. 1914. WESTERN HEMLOCK: ITS FOREST CHARACTERISTICS, PROPERTIES, AND USES. Timberman 15 (12): 25-33, illus. (11) HODGSON, A. H. 1929. LOGGING WASTE IN THE DOUGLAS FIR REGION. West Coast Lumber- man 56 (6): I-IV; (7): V-VIII; (8): IX-XII; (9): XIII-XVIII, (10): XIX-XXIV; (11) : XXV-XXVIII; (12): XXIX-XXXII; (13): XXXIII-XXXVI, illus. Also in Pacific Coast and Pulp Indus. 3 (13): I-XL, illus. (12) __ 1931. PRESENT UTILIZATION OF SAWMILL WASTE IN THE DOUGLAS FIR REGION. Timberman 32 (9): 27-33, illus.; (10): 25-31, illus.; (11): 32-48; (12): 36-46. (13) JOHNSON, R. P. A., and GIBBONS, W. H. 1929. PROPERTIES OF WESTERN HEMLOCK AND THEIR RELATION TO USES OF THE WOOD. U. S. Dept. Agr. Tech. Bull. 139, 62 pp., illus. (14) HUNGER, T. T. 1934. THE PULPWOOD FORESTS OF OREGON AND WASHINGTON. Pacific Pulp & Paper Indus. 8 (9) : 20-23, illus. (15) TEMPLETON, H. L., and SHERRARD, E. C. 1926. TANNIN CONTENT OF WESTERN HEMLOCK AFTER IMMERSION IN SEA WATER. Indus, and Engin. Chem. 18: 101-102. (16) 1912. WESTERN HEMLOCK TSUGA HETEROPHYLLA (RAF.) SARGENT. U. S. Dept. Agr., Forest Serv. Silvical Leaflet 45, 6 pp. (17) UNITED STATES DEPARTMENT OF COMMERCE, BUREAU OF THE CENSUS. 1921-31. THE LEATHER INDUSTRIES. U. S. Dept. Com., Bur. of the Census, Ann. Repts. (18) 1923-31. CONSUMPTION OF VEGETABLE TANNING MATERIALS. U. S. Dept. Com., Bur. of the Census, Bien. Repts. ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE WHEN THIS PUBLICATION WAS LAST PRINTED

Secretary of Agriculture L HENRY A. WALLACE. Under Secretary M. L. W^ILSON. Assistant Secretary-_J HARRY L. BROWN. Director of Extension Work • C. W. WARBURTON. Director of Finance W. A. JUMP. Director of Information M. S. EISENHOW ER. Director of Personnel W. W. STOCKBERGER. Director of Research JAMES T. JARDINE. Solicitor MASTíN G. WHITE. Agricultural Adjustment Administration H. R. TOLLEY, Administrator. Bureau of Agricultural Economics A. G. BLACK, Chief. Bureau of Agricultural Engineering S. H. MCCRORY, Chief. Bureau of Animal Industry JOHN R. MOHLER, Chief. Bureau of Biological Survey IRA N. GABRIELSON, Chief. Bureau of Chemistry and Soils HENRY G. KNIGHT, Chief. Commodity Exchange Administration J. W. T. DUVEL, Chief. Bureau of Dairy Industry O.E. REED, Chief. Bureau of Entomology and Plant Quarantine.^ LEE A. STRONG, Chief. Office of Experiment Stations JAMES T. JARDINE, Chief. v Food and Drug Administration WALTER G. CAMPBELL, Chief. Forest Service FERDINAND A. SILCOX, Chief. Bureau of Home Economics LOUISE STANLEY, Chief. Library CLARIBEL R. BARNETT, Librarian. Bureau of Plant Industry FREDERICK D. RICHEY, Chief. Bureau of Public Roads THOMAS H. MACDONALD, Chief. Resettlement Administration W. W. ALEXANDER, Administrator. Soil Conservation Service H. H. BENNETT, Chief. Weather Bureaba W^ILLIS R. GREGG, Chief.

This bulletin is a contribution from

Bureau of Chemistry and Soils HENRY G. KNIGHT, Chief. Industrial Farm Products Research Division H. T. HERRICK, Principal Chemist^ in Charge. 48

U. S. GOVERNMENT PRINTING OFF!CE:1937