COPPER. 
§ 845-] 
in a healthy state, which is not the case with a percentage of the popu¬ 
lation ; to persons whose liver or kidneys are unsound, even the small 
amounts of copper found in “ coppered ” peas may act as a poison, and 
the experiments previously detailed throw no light upon the action of 
copper under such circumstances. 
§ 845. Detection and Estimation of Copper. —In routine analysis, 
a solution of inorganic salts, acidified only moderately with hydrochloric 
acid, will have been saturated with hydric sulphide, and any precipitate 
treated with ammonium sulphide to dissolve out the sulphides of arsenic, 
antimony, and tin ; the sulphides remaining insoluble may be silver, 
mercury, bismuth, lead, copper, cadmium, zinc, and there may be, if 
platinum vessels have been used, a trace of platinum sulphide. These 
mixed insoluble sulphides are attacked by nitric acid, diluted with its 
own volume of water, and the mixture boiled. Soluble nitrates are 
formed of most of the metals, but sulphide of mercury will not be dis¬ 
solved, nor platinum sulphide—the lead sulphide, if present, will also 
in great part have been converted into sulphate, so that these, with 
free sulphur, can be filtered off. In the nitric acid solution, any silver 
may be detected and separated by hydrochloric acid, lead by dilute 
sulphuric acid, and bismuth by adding an excess of ammonia and 
filtering off any white precipitate. Should copper be present, the 
ammoniacal liquid will be of a blue colour. To separate the copper the 
liquid may be evaporated to dryness, and the nitrate decomposed by 
heating with a little sulphuric acid ; the resulting sulphate is dissolved 
in water, boiled, and to the boiling liquid hyposulphite of sodium 
solution added, which produces a precipitate of cuprous sulphide,. 
Cu 2 S, mixed with sulphur. This sulphide may be readily converted 
into a soluble copper salt and further identified by tests. 
Electrolysis of Copper Salts. —Both as a means of detection and 
estimation of copper, electrolysis is much used. Copper is readily 
deposited from an acidified solution on either bright iron or bright 
zinc. An old method of estimating copper was to treat a solution with 
zinc-foil and dilute sulphuric acid, but this somewhat crude process is 
now but little used. The ordinary process of electrolytic deposition of 
copper is to dissolve up to 1-5 grm. of the substance containing copper 
in dilute sulphuric acid, to add a small quantity of nitric acid, and to 
dilute up ro 130 c.c. with water, using platinum poles ; the anode may 
conveniently be a platinum dish. The solution is heated to about 
60°-65°, and the current should be 2-5-3 amperes and 2 volts. The 
deposit is washed (without interrupting the current) first with water, 
then with alcohol, and finally with ether, and is then carefully dried and 
weighed. Should iron, nickel, or cobalt be present, Kufferath 1 adds 
2 grms. of formaldehyde, which prevents their deposition. 
1 Zeit. angew. Chem., 1904. 
