436 
Messrs. Trowbridge and Stevens 
volatilizes ; so with these it is necessary to resort to ana- 
lytical methods of determining the percentage of each. The 
copper was determined by electrolysis, by precipitating the 
copper, from a sulphuric-acid solution of the alloy, upon a 
platinum disk connected with the negative pole of a battery, 
and the positive pole dipping in the solution. The zinc was 
determined by subtracting the per cent, of copper from a 
hundred per cent. 
The composition of the alloys are given in the tables below, 
and will be referred to by number hereafter. 
Number. 
Alloys of Sn and Pb. 
Number. 
Alloys of Cu and Zn. 
Parts by 
Parts by 
Per cent. 
weight 
ofSn. 
weight 
ofPb. 
ofCu. 
ofZn. 
I. 
1 
9 
I. 
91-92 
8-08 
II. 
2 
8 
II. 
85-75 
14-25 
III. 
3 
7 
III. 
72-99 
2701 
IV. 
4 
6 
V. 
5 
5 
IV. 
66-70 
33-30 
VI. 
6 
4 
v. 
49-32 
50-68 
VII. 
7 
3 
VI. 
27-99 
7201 
VIII. 
8 
2 
IX. 
9 
1 
VII. 
7-53 
92-47 
Four determinations were made with these alloys, the first 
two being the observation of the electromotive force of each 
alloy, with platinum for the positive pole and the alloy as 
the negative pole, with fresh pond-water as the liquid ; the 
second two being the determination of the electromotive force 
with the same positive pole, but with distilled water acidulated 
with a small quantity of sulphuric acid for a liquid. A mirror- 
galvanometer and ground-glass scale were used, and a large 
resistance placed in the circuit, and the galvanometer shunted 
so as to reduce the deflection. 
The first two tables do not give any general law for the 
electromotive force of alloys, the force being especially irre- 
gular, which is perhaps due to the fact that the electromotive 
forces of the two metals are very nearly alike. 
The explanation of the third table is rather unsatisfactory, 
since the sulphate of lead is insoluble, while the sulphaic of 
tin is not known ; and this last may account for the change 
from the first tables. In the fourth table, the increase in 
electromotive force of the alloys' containing the more copper 
may be accouuted for by the fact that the sulphate of copper 
is more readily soluble than the sulphate of zinc. 
