50 
examining the current with the galvanometer, we shall find 
the intensity represented by from eight to nine grains (the 
sulphate of copper arrangement not being constant in inten- 
sity) ; thus the decomposition of the copper by the hydrogen 
diminishes the electro-motive force, which we may conceive 
to arise from the decomposition of the zinc, less by four 
grains than when the hydrogen is given off in a gaseous 
form. Again, if for the copper in sulphate of copper we 
substitute a plate of platina in nitric acid, a diaphragm 
being used as before, the nitric acid will be decomposed 
at the surface of the platina, water being formed, and a 
gaseous compound of nitrogen, containing less oxygen than 
nitric acid, is given off. We shall now find the intensity 
of the combination sixteen grains, thus affording, by twelve 
grains, less diminution of intensity than when the hydrogen 
is given off in a gaseous form; by eight less than when 
copper is precipitated by the nascent hydrogen. 
We also find that with various metals there are various 
degrees of electro-motive force ; and these, whether they 
be employed as the positive or negative element of the 
combination, appear pretty nearly to maintain a like rela- 
tion to each other in the scale of electro-motive force. 
This will be seen on inspection of the accompanying tables, 
in which we shall find the electro-motive power of zinc to 
iron in sulphuric acid to be about 16 to 11.2, or 2.8 degrees 
more, whatever negative metal be used in combination there- 
with in the same cell. 
But metals in voltaic combinations appear to acquire 
different relations of electro-motive force, (that is, according 
to the old form of expression, become positive or negative,) 
according to the other metal with which they are associated 
in a voltaic pair. Thus, if we associate copper with zinc 
in dilute sulphuric acid, as before-mentioned, the zinc is 
oxydated, and hydrogen is thrown off from the surface of 
