584 MINERALOGY 



qualitative test for gold is required, the residue from the mercury 

 is tested in the wet way as below ; cupellation and parting are not 

 necessary. 



Ores and minerals containing considerable gold may be treated 

 in the same manner as the silver assay, p. 578. 



6. Wet test. The powdered mineral, or residue of gold from 

 the cupel, is dissolved in nitro-hydrochloric acid, diluted and 

 filtered, the solution evaporated nearly to dryness to drive off 

 free acid, diluted with water, and a solution of ferrous sulphate 

 added, when the gold will be reduced to the metallic state and 

 precipitated in the form of a brown powder, but if the quantity 

 is very small, the solution will be colored bluish or purple by the 

 fine particles of suspended gold. 



Tin, Sn. Atomic weight, 119. Fusing point, 232 C. 



a. Reduction test. The powdered mineral, if a sulphide, is 

 first roasted, then mixed with soda, borax, and coal dust, reduced 

 and washed as described under lead, p. 579. The tin globules 

 are white and malleable. They may be mistaken for silver, from 

 which they are distinguished by yielding insoluble white meta- 

 stannic acid on heating in a test tube with HN0 3 ; also see coat 

 below. 



On heating in the R. F. the charge is well fused, but the flame 

 should not be continued long, as tin after reduction is easily vola- 

 tilized, when no buttons will be found in the charge, upon wash- 

 ing in the mortar. 



6. Tin is easily volatile, forming an oxide coat, very near the 

 assay, yellow while hot and white on cooling. In making the 

 reduction test the coal should always be examined for a coat. 

 Tin and zinc coats are much alike in their position on the coal, 

 color, and both are volatilized with difficulty. If the tin coat is 

 moistened with cobalt solution and heated with the O. F., it 

 will become blue or bluish green when cold. A zinc coat will 

 become grass-green. 



Illustration. r Use cassiterite, SnOg. If the reduction test a is 

 heated for a longer time, the tin coat of b will appear. 



Antimony, Sb. Atomic weight, 120.2. Fusing point, 630 C. 



a. Coat. Compounds of antimony when heated on coal in 

 the R. F. are reduced to metal ; in some cases it is necessary to 

 roast the charge in O. F. before reduction, but in all cases the 

 metal after reduction is volatilized, yielding a white oxide coat, 

 Sb 2 3 , which settles at a considerable distance from the assay. 



