CHAPTER IX. 



ASSAY OF GOLD. 



Various methods. Fluxes, reagents, &c. General treatment of ores, 

 Preparation of the sample. Weighing, &c. Assay ton. To 

 construct a simple button balance and to use it. Dry assay for 

 gold and silver. Apparatus and procedure. Fusion in a cru- 

 cible. Scorification. Cupellation. Indications of the presence 

 of metals known from cupel stains. To make cupels. Dry 

 assay for lead in galena, tin, antimony. Wet assays for gold, 

 silver, lead, copper, iron. Roasting. Mechanical assay of ores. 



To determine the amount of metal in an ore, there are two 

 kinds of assay adopted. 



The dry method (i.e. by fusing the powdered ore with or 

 without fluxes). 



The wet method (i.e. by the agency of liquids). 



In the principal wet assay, the ore is thoroughly dissolved 

 in acids, and, by the addition of reagents, precipitates con- 

 taining the metals are thrown down. 



In some assays, particularly those of copper, iron, zinc, 

 and silver, a standard solution of known strength is added 

 to the original solution by allowing it to drop gradually from 

 a graduated burette, and when a certain change of colour 

 has been produced, by reading off the graduated mark at the 

 top of the liquid column in the burette the amount of metal 

 in the ore can be accurately determined by a slight calcula- 

 tion. At the same time more simple methods will, if not 

 strictly accurate, give good results, and are more likely to be 

 adopted by the prospector. 



Then there is the assay by mechanical means (for instance, 

 the separating of the lighter portions from heavier by means 

 of water, as in the " panning out " of gold in a deposit), (see 

 GOLD, Chap. V.). 



In dry assays, crucibles or scorifiers capable of standing 

 very great heat, without breaking, are generally used for 



