E U. S. P. Test for Heavy As Paper, Cardboard, * “Solid Fiber” Boards, Gummed Metals
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138 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY Val. 11, KO.2 111-In addition to the puncture test, the Webb the U. S. Geological Survey and with manufacturers machine may be used for tensile tests, elongation tests, of zinc oxide. It was learned from Mr. C. E. Sieben- and compression tests. The tensile test, especially thal of the U. S. Geological Survey that one company when “across the grain,” is an important index of the producing zinc in the United States owned a mine value of a fiber box as a shipping container. This which contained no lead minerals and, therefore, “across the grain” value may also be found more should be able to produce zinc oxide free from lead. quickly by a puncture test, using the “wedge” plunger. It would seem probable that zinc oxide made from IV-The pocket-size model makes it possible to test electrolytic zinc should be free from lead. It was corrugated boxes under conditions which are impossible learned from manufacturers that zinc oxide was being at present. made according to both of these principles, and that V-Besides corrugated products, the Webb machine the products contained much less lead than the amount can be used for testing many other flat substances, such necessary to respond to the U. S. P. test for heavy as paper, cardboard, * “solid fiber” boards, gummed metals. tape, fabrics, etc. TEST FOR LEAD IN ZINC OXIDE BY THE U. S. P. TEST FOR MELLONINSTITUTB OB INDUSTRIALRESEARCH HEAVY MET\ALS UNIVERSITYOF PITTSBURGH.PITTSBURGH, PA. In order to determine the sensitiveness of the U. S. LEAD IN PHARMACEUTICAL ZINC OXIDE P. test for lead in zinc oxide, two series of experiments By W. D. COLLINSAND W. F. CLARKE were conducted entirely independently in order to Received July 25, 1918 establish the limits of sensitiveness. Different quanti- ties of lead from a solution of lead nitrate were made Soon after the outbreak of the present war, difficulty up with zinc oxide and hydrochloric acid so as to give was experienced in obtaining pharmaceutical zinc the concentrations of zinc and acid prescribed by the oxide which would meet the requirements of the U.’S. for the test for heavy metals. In one series Ulzited States Pharmacopoeia. When the matter was P. of tests (W. F. C.), the hydrogen sulfide used was first considered, the statement was made that zinc made according to the directions of the Pharma- oxide of the required purity was very easy to obtain. copoeia. In the other series of tests (W. D. the It was even stated that material bought for use as a e.), hydrogen sulfide used was prepared in the ordinary pigment in painting might be more nearly free from manner by the use of hydrochloric acid and ferrous lead than a certain sample of pharmaceutical zinc sulfide and the gas was washed through water. No oxide which contained about 0.2 per cent of lead. difference could be detectcd in the results by the two Mr. C. L. Black of the Philadelphia Station of the methods. Bureau of Chemistry reported in May that 1917 It was found that a sample of zinc oxide might con- analysis of such samples of zinc oxide as could be tain as much as per cent lead and fail to respond procured on the market at that time indicated that 0.05 to the test for heavy metals. In some cases the test practically all the zinc oxide obtainable contained would be obtained and in others it would fail. When more lead than was permitted by the U. S. P. test. the sample contained as much as 0.I per cent, a positive Some manufacturers at this time stated on the labels test was always obtained and with any amount greater that the zinc oxide sold by them contained heavy than 0.05 per cent there was rarely any doubt about metals slightly in excess of the U. S. limit. Prof. P. the response to the test. C. H. La Wall’ published an article calling attention to this matter and made the suggestion that all samples SAMPLES of pharmaceutical zinc oxide should be tested for lead. A number of samples of zinc oxide were purchased In order to learn whether it would be possible at various drug stores. Some samples were furnished to obtain zinc oxide reasonably free from lead, by manufacturers and others were obtained from samples were obtained on the market and from dealers through the regular purchasing office of the manufacturers, and the question was taken up with Bureau. TABLEI-ZINC OXIDE SAMPLE Producer or Lead u. s. P. NO. Received Dealer Manufacturer Per cent Test Remarks 117 ................................. 1-13-17 A ? 0.25 + Purchased at local drug store 118... ............................... 1-16-17 B 0.036 0 Purchased at local drug store 119.. ............................... 1-16-17 A d 0.25 f Purchased at local drug store 133.. ............................... 84-17 D E 0.19 Purchased at local drug store 134.. 8-4-1 7 F G 0.19 + Purchased at local drug store 137 ... 8-6- 1 7 B C 0.26 + Purchased at local drug store 130.. , ............................... 1915 K H 0.041 0 From Bureau stock of reagents 148.. ............................... 9-27-1 7 I I 0.006 0 Show sample from office of manufacturer 158.. ............................... 11-28-17 I I 0.004 0 Sample sent by manufacturer 159... ............................... 11-29-17 I I 0.008 0 Sample sent by manufacturer 155... ............................... 11-5-17 C K 0.013 0 Purchased by Bureau Supply Office 178... ............................... 2-1-18 H I 0.004 0 Purchased by Bureau Supply Office 187.. ............................... 2-4- 1 8 I, I 0.008 0 Purchased by Bureau Supply Office METALLICZINC 149 .................................. 1914 .. M 0.026 .. Analysis on label lead 0.01 per cent 145 .................................. 1917 N M probably 0.094 .. Analysis on label: lead none 146 .................................. 9-26-17 .. K 0.012 .. Sample furnished by manufacturer PIGMENTZINC OXIDE 135 .................................. 8-4- 1 7 0 .. 0.13 Trace About 22 per cent barium sulfate 136. ................................. 8-4-1 7 P .. 53.2 Heavy 1 Am. J. Phaum., 89 (1917), 353-5. In a later article (Ibid., 90 (1918), 499). Professor La Wall notes that U. S. P. zinc oxide is now on the market. He proposes tests for lead which will detect 0.03 per cent PbO in zincoxide, while the present U.S. P test under the best conditions will detect 0.05 per cent. Feb., 1919 THE JOURiYAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY *39 Samples of zinc oxide were also purchased at two these troubles are aggravated since the precipitate and paint stores. A few samples of metallic zinc were ex- liquid tend to creep under the paper filter, especially aminedfor their content of lead. if continuous vacuum is not maintained, thus requiriqg a second filtration. NETHOD OF ANALYSIS I Lead was determined by the well-known method of separating as sulfate and weighing as chromate. From 5 to 40 g. of zinc oxide or zinc were dissolved in water and sulfuric acid, with a slight excess of acid. The volume was usually about IOO cc. for IO g. of zinc oxide. Alcohol (gj per cent) was added in quantity just short of that necessary to start precip- itation of the zinc sulfate, usually making about one-third of the final volume. The solution was allowed to stand over night; the lead sulfate was filtered off on asbestos, washed with 50 per cent alcohol, and dissolved in ammonium acetate. The lead was reprecipitated as chromate, after acidifying with acetic acid, by adding potassium dichromate solution. After standing over night, the lead chromate was filtered on asbestos in a weighed Gooch crucible, I dried to constant weight at IIO', and weighed. The accompanying table gives descriptions of the samples and the results obtained for lead, and also the results "ra States 4 of testing according to the United Phayma- 'I copoeia. i? SUMlLlA RY t? For a short time after the beginning of the war it was not possible to procure zinc oxide of the U. S. P. f standard produced in the United States. The U. S. P. test for heavy metals will not detect \ less than 0.0; per cent of lead in zinc oxide. It is possible at the present time to obtain zinc oxide which, with respect to the presence of lead, is of much higher quality than is called for by the re- quirements of the U. S. P. BUREAUOF CHEMISTRY U s. DEPARTMENTOF AGRICULTURE WASHINGTON,D. C. AN EFFICIENT LABORATORY FUNNEL FOR FILTERING NEUTRAL LIQUIDS, ESPECIALLY THE VOLATILE ORGANIC SOLVENTS By T. E. ALDRICH Received October 23, 1918 Those who have had occasion in the laboratory to collect precipitates suspended in ether, chloroform, acetone, alcohol, or mixtures of these organic solvents, especially by forced filtration, have no doubt at times experienced trouble when using the ordinary funnel and especially the Buchner funnel. In Ihe case of aqueous solutions, the filter paper, after being moistened and pressed closely to the funnel for the purpose of removing bubbles of air that inter- fere with filtration, adheres closely to the glass and FIG.1 filtration is ordinarily rapid, while in the case of ether, The advantage of the funnel to be shortly described for example, the solvent being volatile passes away lies in the fact that the filter paper is clamped securely rapidly, and channels and spaces are formed between between two plates by a screw thread so that it cannot the paper and the funnel; the paper tending to lift lift even when the filtration is interrupted, and thus from the glass.