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Correspondence Proceedings.] DISCUSSION ON GOLD-QUARTZREDUCTION. 177 sufficient to pay when the material was properly worked, they Mr. Giles. could see how imperative it was that themachines for reducing the ore should be of the most perfect description. It was remarkable to observe that the discussion had been maintained in many cases by young members; that perhaps proved that mining, though as old as the hills, was still endowed with vitality. For looking at what had taken place at Fort Salisbury, where pre-historic build- ings hadbeen discovered which wereassumed to be connected with the gold-mining industry of the days of King Solomon, they ought to be able to continue that industry, and to make it pay. There was good reason todoubt whether the meansadopted for ex- tracting gold in those days were anythinglike as perfect as those of the present day. In view of the large income derived from gold-mining, a great many consi.derations would be suggested by the Paper, which would be well worth attention in the future. Correspondence. Mr. G. ATTWOODwas much struck with the care and general Mr. Attwood. accuracy of the Author’s statements. The subject was a difficult one to handle on account of the numerous inventions which had been made during the last thirty yearsfor the purpose of improv- ing gold-quartz reduction; nearly all the inventions having some good points but failing in the main. The result of practice had reduced the machines most extensively employed to gravitation and steam-stamps, the Erom or similar rolls, and the Blake jaw- crusher. Withregard to the Author’s statement that effective work was done only at the instant that the stamp descended on the ore, it was possible that such was the case in the early days when the stamp was made in square or angular forms ; but when the revolving stamps were brought into use, a rotary motion was givento the stamp as well as the blow, whichcontributed a grinding motion aswell as a pounding one. This action could easily be seen by watching a battery at work with the screens removed. In reply to an objection to stamps brought forward by the Author, hepointed out that modern gravitation-stamps were so arranged that, with ordinary care, no oil or greaseshould con- taminate the ore either in the battery or in the feeding-hopper. For the last twenty-five years he had been lookingfor a wet- crushing machine that would supersede the gravitation-stamp, and he was still unable to recommend any other appliance. Even for [THE INST. C.E. VOL. CVIII.] N 178 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes of Mr. Attwood. dry crushing he had found the stamp equal to jaw-breakers and rolls. Indeedat the great Comstock lode in Nevada, wherehe was engaged for nine years, at a time when no expense was spared in trying every newform of machinery, the gravitation-stamp was selected in spite of its many defects. The steam-stamp had been brought to great perfection in the Lake Superior copper district, and he had recently seen at the Calumet and Hecla mines a mill of fifteen stamps pounding 2,500 tons per day of conglomerate, Fig. 24. THESCHBANZ STOKE-BREAKER. containing native copper ; the scrcens in that case being made of steel plates with circular punched holes about inch diameter. Mr. Bellom. Mr. MAuRrCE BELLOM(Paris) wished to compare thestone- breakers described by the Author with a machine, known as the Schranz stone-breaker, he had recently seen at work in Germany. In this machine the ore was subjected to a simultaneous crushing andgrinding motion. The accompanying drawing (Fig. 24) indicated the construction of the machine so clearly that it was merely necessary to add a few details. The two jaws were made Proceedings.] CORRESPONDENCE ON GOLD-QUARTZREDUCTION. 179 of cast-steel, and the space between them might be regulated at Mr. Bellom. will by means of a vertical screw V, which adjusted the wedge C. The short connecting rod B of cast-iron, had been designed with such section that it would be broken before any other part of the stone-breaker, if some veryhard material should find itsway between the jaws.Deta,ils of the different sizes in whichthis machine was made would be seen from the Table given below. Theadvantages of this machine consisted inthe fineness to w"hich the ore could be brought (8 millimetres), and inthe fact that there was no necessity to employ the trommels usually adopted with Americanstone-breakers. By reason of theacute angle at which the jaws were placed, the Schranz stone-breaker performed the functionof the tromnlel, the jaws beingable to seize and crush the pieces of ore, the size of which prevented them from engaging between t,he surfaces of the cylinders, whose angle could not be reduced below a certain limit without giving to the diameter of these cylinders an exaggerated size. With his contribution to the discussion, Mr. Bellom sent a lengthy statement of the mathe- . matical principles on which the construction of this machine was base&. - 11. 111. 1V. v. 300 X' 400 X 500 X' 600 X , , I 200 I 250 300 350 Number of revolutionsper minute of thedriving pulley} 250 250 250 250 250 Diameter of the driving pulley 500 650 700 1,000 millimetres} 400 Width of the driving pulley . 125 150 160 180 millimetres} 100 1,450 1,650 1,800 1,950 900 1,150 1,400 1,700 2,000 900 1,150 1,350 1,550 1,650 Weight of the machine . 2,500 4,500 6,500 9,000 kilograms} 8oo Weight of one pair of jaws 200 300 400 500 kilograms} 100 HP. 1-2 3-4 5-6 8-10 10-12 Quantity of orecrushed . 600-7 '1,500-' 2,000-' 3,000-' 4,000- kilograms per hour} $1,000 J .2,000 , 3,000 J 4,000 , 5,000 Mr. R. BOLTONobserved that the Author gave descriptions of Mr. Bolton. rock-breaking mechanisms in which the breaker-jaw was hinged above and in which it was hinged below, to the advantage of the latter.There was, however, afu.rther form, employed inthe Lancaster stone-breaker, made by Messrs. Penny & Company, of Lincoln. It was largely used in the United States, its peculiarity N2 180 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Bfinutes of Mr. Bolton. being that the jaw was hungon a toggle, or vibrating link, above and attached to the reciprocating armbelow, whereby a compound motion was attained with very beneficial results as to output and regularity of size. Themachine further possessed simplea mechanical arrangement of driving-gear by a double cam on the driving shaft, upon which wasa broad iron roller fixed to the reciprocating-arm. This had the effect, as compared with eccen- trics or cranks, of doublingthe number of reciprocations at a given speed and of reducing the friction of driving. By a simple mechanism of one lever resting upon another, a control over the stroke of the jaw was attained duringoperation, and the size of the product might be varied in size at will. This machine seemed to possess advantages demanding attention. One of Sholl's pneumatic stamps was worked for some years near St. Austell, and very fine crushing was done with it. The death of the inventor had since then prevented the extension of his system; but there was a good deal to be said in favour of the use of a cushion of air in high- speed stamping.The Huntington mill, with the improvements in detail introduced into it by Mr. Paxman, certainly formed, in Mr. Bolton's opinion, the best fine-crusher in the market. Mr. Chenhall. Mr. J. W. CHEKHALLobserved that,notwithstanding the long indictment of defects adherent to the stamp-mill brought forward by the Author, it still held its own as the most effective machine, and the one most cheaply manufactured and manipulated, in the market. This arose from the fact that the mill-man could always rely-when he had a well-constructed stamp-mill-on the quan- tities he could pulverize, and on the results he could obtain. As a pulverizing-machine no other contrivance could compete with it in effectiveness. Steam-stamps have been very successful intheir application to the crushingof copper ores on Lake Superior, where it was not necessary to carry the stamping to so great a degree of fineness asin the case of gold-quartz reduction. TheHusband quick-speed stamps had also been successful to some extent in the stamping of tin-stone in Cornwall. The stamp-mill, however, could not be considered well adapted for dry stamping, the con- tinued concussion of the stamps making it impossible to collect thedust from the battery-box. This accumulation of dustwas very injurious to the workmen employed in the mill. He had had experience inthe crushing for dressing of largequantities of copper ore by means of modified Erom rolls, used as wet crushing machines. In this case it was unnecessaryto crushvery fine, and, consequently, large quantities could be crushed, the output per day amounting to 1,000 tons with six sets of rolls, each set Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 181 containing three pairs of rolls. The work was very satisfactory ; Mr. Chenhall. but any attempt to increase the fineness influenced the output very largely, and the grooving of the surface of the rolls could never be entirelyprevented. All the rolls and roll-shaftswere consequentlymade in duplicate, andthe rollers were removed immediately they showed signs of wear from the last mill to the higher set of rolls, where the crushing was less fine.
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