Lawrence Scientific School. 65 
In seven determinations of copper in the alloy of copper and 
nickel employed by the government for small coins, the follow- 
ing results were obtained: 
Number. Weight of alloy. Copper. Percentage. 
i 0-4 0°3640 87°50 
Il. 0°6180 0°5410 87°54 
IIL. 0°4609 0°4090 88°91 
IV. 0°5120 04481 87°51 
¥. 0°4220 0°2693 87°51 
VI. 0°2525 02225 8811 
VII. 0°3705 0'3255 87°85 
The percentage of copper required by the formula CuO, 
S0,+5HO is 25:42, while the government standard alloy of 
nickel and copper contains 87°50 per cent of copper. The time 
required for precipitation varied from one to three hours, the 
separation of the last traces of copper being in each ease deter- 
mined by testing a drop of the liquid upon a porcelain plate 
with sulphuretted hydrogen water. The copper, after precipita- 
tion, was washed with distilled water, dried in vacuo over sul- 
phuric acid, and weighed with the platinum vessel. The only 
precaution necessary is to regulate the strength of the current so 
that the copper may be precipitated as a compact and bright 
metallic coating, and to dry as quickly as possible. hen the 
copper is thrown down in a spongy condition, it not only oxyd- 
izes rapidly, but it is impossible to wash out the last traces of 
foreign matter contained in the solution. This is well shown by 
number III and number VI of the second series, in bot 
which cases the copper was precipitated too rapidly. The solu- 
tion from which the copper has been deposited contains the 
other elements present in the original substance. It may 
easily poured off without loss, and the washings added. — 
It appears at least probable that nickel may be determined by 
electrolysis in the same manner as copper, the solution employed 
Ing the ammoniacal sulphate with excess of freeammonia. Mr. 
MCandless obtained in two determinations in a commercial sam- 
ple 91-26 and 91°60 per cent nickel. In both cases the nickel 
Was thrown down completely as a bright coherent metallic coat- 
ing upon the platinum. 
Cambridge, Oct. 1st, 1864. 
Au. Jour. Sc1.—Szconp Srnres, Vou. XXXIX, No. 115.—Jan., 1865. 
9 
