ASSAYING. 635 



GUI'); the bar obtaiued is about oue inch thick (Fig. 7, Plate XLV). Four pieces are 

 detaclicd from it witli chisel aud hammer, as shown in a, Fig. 7. One-half an assay 

 ton is weighed from each i)iece, and cupelled, and the assay carried ou as usual. 



Gold assays.— Gold assays are made by dissolving the silver buttons in weak 

 nitric acid, as usual. 



Lead assays — Ores and slags are assayed for lead in the crucible. Five grams 

 of the pulverized oi-e or slag are mixed with 15 grams of a tlus composed of 



Boras 1 part. 



Bicarbouatc of soda 4 parts. 



Argol 1 part. 



Flour i part. 



or some analogous flux. The mixture is fused, with or without the addition of an iron 

 nail or rod, either in the crucible or the mufile-furuace. When the muffle is used, the 

 crucibles, I'epresented in Fig. 5, Plate XLIII, are placed in it, tocether with large pieces 

 of charcoal, to produce a reducing atmosi)here, and the front of the muffle is kept closed. 

 In both crucible and scoriflcation assays the lead buttons and slags, when taken out of 

 the furnace, are rapidly poured into the molds, shown in Figs. 1 and 2, Plate XLIII. 

 In lead assaying the button of lead, detached from the slag after cooling, is weighed 

 in grams and its fractions, and the result, multiplied by 20, gives the percentage. 



Iron assays — The ores are assayed for iron by Marguerite's well-known burette 

 process, with a standard solution of permanganate of potash. 



Estimation of gangue — Gangue is determined by dissolving the ore in strong hydro- 

 chloric acid, or aqua-regia, collecting the insoluble residue on a filter, washing well, 

 calcining, and weighing. Some assayers evaporate the solution to dryness at 100° G. 

 before filtering, in order to estimate both gangue and soluble silica. 



Estimation of moisture — Moisture is determined in the ores by desiccation of one 

 pound of ore placed in a copper pan over the muffle-furnace, or over a sand-bath 

 heated by a kerosene lamj). 



Specific gravity determinations — This operation is performed every day at a few 

 smelters ou the slags of each furnace. It seems an unnecessary operation, first, because 

 superintendents ought to rely solely upon careful assays for lead and silver; second, 

 because, with a little practical experience, the mere appearance of the slag is more 

 reliable than its specific gravity ; third, because those who determine daily the specific 

 gravity of slags and their contents iu lead and silver have never been able to find a 

 relation between the three data. In the analytical study on the slags made specially 

 for this report it will be seen that there is no relation whatever between the contents 

 of lead and silver; and at the smelters it is admitted that the specific gravity of slag 

 may be raised by other substances thau lead — by iron, for instance. 



The specific gravity determinations are carefully made by means of the Jolly 

 specific gravity spring-balance, represented in Fig. 2, Plate XXXVIII. This instru- 

 ment consists of a wooden gallows-frame, at the end of whose horizontal beam is sus- 

 pended a delicate wire spring, provided with a small ivory index, J, and a small brass 

 liaii, P, suspended from the sjjriug by three wires. Ou the face of the vertical beam, 

 looking towards the spring, is a mirror, carefully graduated iu millimeters. A beaker, 

 three-fourths filled with distilled water, is placed on a stand, *', which is provided 

 with a set-screw, and moves up and down the vertical beam. 



