INSTRUMENTS AND CHEMICAL TESTS 583 



of gold which have been flattened in the grinding; if any are found, 

 they are ndded to the ground sample. The sample i> placed in a 

 tin >r iron pan 2 in. deep and 8 in. across; 2 cc. of mercury is 

 added, the pan is filled with water, taken in the hands, and shaken 

 with a circular motion ; by this motion the sample is stratified and 

 the materials will be arranged according to their specific gravity, 

 with the heavier particles in the bottom, where the gold will come 

 in contact with the mercury and form an amalgam. With care 

 the light materials may be allowed to flow over the side of the 

 pan, especially if a stream of water is running through it at the 

 same time it is shaken with a circular motion, throwing the light 

 particles to the top. If the heavy concentrates contain pyrite, 

 they should be dried, and roasted to drive off the sulphur, then 

 ground and repanned with the same mercury. Finally all heavy 

 material together with the mercury is washed in the mortar and 

 ground under water, also allowing a stream to flow through it, 

 which is so regulated as to carry the light materials, as they are 

 ground, over the edge, leaving in a very short time the clean 

 bright mercury which contains the gold. The mercury is poured 

 on a thick piece of chamois or buckskin, folded up, and most of 

 the mercury is squeezed through; if the chamois is thick and 

 tight, only mercury will pass through, the gold amalgam remain- 

 ing. This is transferred to a porcelain crucible, heated gently at 

 first, and finally to redness, to volatilize the mercury ; or if there 

 is only a small quantity of amalgam, the mercury may be driven 

 off with the O. F. on coal. In either case the residue contains 

 gold and silver, which is collected on a small piece of sheet lead : 

 and to insure enough silver for parting, pure silver to twice the 

 amount of the residue is folded with it in the lead and fused in 

 the O. F. ; then cupeled as in the case of silver, p. 578. The 

 button of gold and silver if large is flattened on the anvil, and 

 parted; that is, the gold is separated from the silver. After 

 flattening the button it is heated with 2 cc. of dilute nitric acid in 

 a porcelain crucible ; heating serves to start the reaction and then it 

 is allowed to proceed slowly. The nitric acid dissolves the silver, 

 leaving the gold as a black-looking powder or a brownish, spongy 

 mass. The nitric acid is decanted. The gold is treated in the 

 same way with strong nitric acid, decanted, and washed with 

 water. If the sample was weighed in the beginning and the 

 operation carried through with care, the gold residue may be 

 weighed and will represent a fair assay of the ore. When only a 



