518 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISIM 



this kind possesses a remarkable constancy, provided there are no 

 secondary effects arising from the precipitation of the negative metal 

 upon the positive plate. It may happen that some particle of the zinc 

 may not be well amalgamated ; in that case a direct action of the acid 

 upon the zinc takes place, there is a development of hydrogen in that 

 place, the negative metal accidentally dissolved in this liquid will be 

 reduced in it by the gas, and there will be a partial pile, which will 

 affect the principal action. These partial effects will be propagated by 

 degrees over the whole surface, the positive state of which will then 

 rapidly decrease. This will only take place when the negative metal 

 is soluble in the acid. 



12. 



I have made many experiments on this subject. A thin plate of zinc of 

 seven inches square, and weighing 848 gr., was amalgamated, in order 

 to form a voltaic pair with a plate of copper of the same size. The 

 liquid was sulphuric acid, of a specific gravity of 1*105. There was 

 no development of gas on the surface of the zinc : the bubbles of air 

 which formed there by degrees rose so slowly, that they might with 

 propriety have been disregarded, even if there had not been reason to 

 believe that they were for the most part the atmospheric air contained 

 in the water. After five hours of action the plate was again weighed, 

 and had lost only 1 12 gr. ; during this time the pair of plates had been 

 twice withdrawn from the acid, and dried for five or six minutes near 

 a stove. 



The following is the table of the deviations of the needle which de- 

 note the decrease of the energy of the current. 



The following day the experiments were repeated with the same 

 pair of plates. The decrease of the deviation was not so rapid as be- 

 fore, and the original energy always restorable by drying the plates ; 

 once it even increased to 65°. At lO*^ 50' in the evening the devia- 

 tion was still at 55°. The action must have continued through the 

 night, but the next morning the plate was found broken in pieces. Amal- 



