518 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM 
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 zine 
may not be well amalgamated; in that case a direct action of the acid 
upon the zine 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. 
Ihave 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 1105. ‘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 112 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twice withdrawn from the acid, and dried for five or six minutes near 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. 
Time. Deviation. Time. Deviation. 
St 19! 61° 10° 60° 
ogg! bg? 10® 30! 58° 
8» 30! 58° bey 15 a 
8b 49! 574° the pile|was dried 
8h 56! 562 11's’ | 61° 
95 10! 554° 115 30! 60° 
the pile}was dried 1g 59x? 
9» 16! 62° 198 30! 58° 
9" 30’ 61° in Df? 
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 10" 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- 
