222 



PROCEEDINGS OF THE AMERICAN ACADEMY 



how much of the zinc volatilizes ; so with these it is necessary to re- 

 sort to analytical methods of determining the per cent of each. The 

 copper was determined by electrolysis, by precipitating the copper, 

 from a sulphuric acid solution of the alloy, upon a platinum disk con- 

 nected with the negative pole of a battery, and the positive pole dip- 

 ping 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. 



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 determina- 

 tion 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 electro- 

 motive force of alloys, the force being especially irregular, 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 sulphate of tin is not known ; 

 and this hist may account for the change from the first tables. In 

 the fourth table, the increase in electromotive force of the alloys con- 

 taining the more copper may be accounted for by the fact that the 

 sulphate of copper is more readily soluble than the sulphate of zinc. 



