ASSAYll^G. 633 



woodfi) liaiidle. Giiiiding is jieiforiiu'd by placing the left liaiul on the biicker, hold- 

 ing the handle in the right hand, and moving the bncker forwards and backwards, 

 at the same time lifting and lowering the handle, and exerting a slight pressure with 

 the left hand. While all this is going on the bncker is also moved from the left to the 

 right side, and inversely, so as to incre.'se the grinding surface. All this is much 

 more easily i)erformed than described. 



The pulverized ore is then passed through sieves of 70 to 80 meshes to the linear 

 inch, represented in Fig. 8, Plate XLIII, in elevation. The metallic cloth of the sieve 

 is made of brass. It is adjusted to a tinned-iron circular frame, b. fitting in a circular 

 tinned-iron box, or dust-receiver, a. This is a very convenii^ut arrangement, the loss 

 in dust is very small, and the mixing of the dust takes place at the same time as the 

 sifting. 



Crucibles and scorifiers — Figs. 3, 4, and ."), Plate XLIII, represent the crucibles, 

 scoriflers, and gokl-auuealing cups, which are manufactured by the Denver Fire Clay 

 Company. The gold-annealiug cups and scorifiers are similar to the European ones 

 in ajipearance, but greatly inferior to them in quality. The assay crucibles, three-six- 

 teenths of an inch thick, are probably the thinnest clay pots used in assaying in any 

 country. They are very convenient for the reason that, with a low temperature in 

 the furnace, the assay fluxes become easily fluid, but they never stand more than two 

 runs in the crucible furnace. 



Cupels — Cupels are always made in the assay laboratories in brass molds, the 

 process being too well known to demand description. Their form and size are shown 

 in Fig. 0, Plate XLIII. 



Muffles — The nnifHes made by the Denver Fire Clay Company are good. They 

 are generally large enough to hold from 12 to 16 scorifiers, enabling the assayer to 

 assay three or four samples of ore at the same time. 



Tools — The scorifier tongs, cupel tongs, crucible tongs, raking rods, anvils, ham- 

 mei's, chisels, etc., are similar in every respect to those universally used in assaying. 



Slag molds — The molds into which are poured the crucible and scorifier slags are 

 peculiar, and are represented in Figs. 1 and 2, Plate XLIII. They consist of a sheet 

 of cast iron, divided into 12 conical molds. They are very convenient, tbe lead buttons 

 and slags cooling rapidly on account of the thinness and large surface of the mold. 



Fuel — Coke is used in the crucible furnaces and charcoal in the muffle furnaces, 

 but sometimes coke and charcoal are mixed in the muffle furnaces. 



Balances — Balances capable of weighing from four jiouuds to one sixteenth of an 

 ounce are used for the estimation of moisture in the ore; balances weighing from 100 

 grams to 1 milligram, for the weighing of scorifying and crucible assays; and those 

 sensitive to the tenth of a milligram, for the weighing of silver prills and gold ])art- 

 ings. These balances are generally manufactured by Becker & Sons, of New York. 

 They offer no peculiarity in construction. 



The iceights used in assaying are gramme weights for lead, iron, and gangue 

 assays, and silver prills, or gold partings; but the ore, slags, and bullion are weighed 

 in assay tons, whose symbol is A. T., or its subdivisions. The weight boxes contain 

 one tenth of an assay ton, or -^ A. T., ^ A. T.. f-g A. T., 1 A. T., 2 A. T. Some boxes 

 contain besides „V A. T. and 5 A. T. The system of assay ton weights introduced by 

 Prof. C. F. Chandler, of the School of Mines, Columbia College, Xew York, is as siuiple 

 as it is ingenious. The ton of 2,000 pounds avoirdupois is equal to 32,000 ounces 



