122 THE PROSPECTOR'S HANDBOOK. 



solution. Filter or decant the solution. The residue 

 sulphate of lead nearly represents 68 percent, of metallic 

 lead. 



Copper. 



The most accurate method of determining the amount 

 of copper in an ore is to thoroughly dissolve the ore in 

 acid, then to add ammonia until a blue colour is obtained, 

 and then to drop from a graduated burette a standard solu- 

 tion of cyanide of potassium until the solution has the colour 

 taken out of it. 



Number of markings on burette : present reading : : 

 known strength of solution : x where x is the number of 

 grains of copper in the weighed portion of the ore. 



X 100 = percentage of copper in the ore. 



weight of ore 



The burette method, like the dry assay, requires great 

 care in order to insure accuracy, and might mislead one 

 who has not studied and practised it, as certain metals other 

 than copper may sadly affect the results. On this account 

 there is no occasion for explaining the process in detail, as 

 the prospector will find the following method comparatively 

 simple. 



Take finely powdered ore, say 25 grains, drive off 

 sulphur, &<i ; by roasting (q.v.) in a porcelain dish. 



Dissolve by heating in nitric acid. Add a little sulphuric 

 acid and evaporate to dryness. Dilute in water and pour 

 the solution into a basin. If well polished sheet or other 

 iron be placed in it, and left for an hour or so, the metallic 

 copper will form on its surface, and by means of a feather 

 may be rubbed off and weighed. 



Or else (to avoid roasting). Moisten the powdered ore 

 in sulphuric acid, and add nitric acid. Let it be thus heated 

 for about an hour or so, and let nitric acid be constantly 

 added during the operation. Add hydrochloric acid to get 

 rid of nitric acid, which may be judged by absence of 

 chlorine smells. Dilute with water and obtain copper on 

 the inserted iron as before. To see that all the copper has 

 been properly deposited, dip the polished point of a knife- 



