424 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND 
sary that a portion of the water and the acid should be decomposed, in 
order to obtain hydrogen and azote. As to the oxygen, it oxidizes the 
lower part of the plate. The decompositions take place in such propor- 
tions that all the elements arising from them are employed to form new 
compounds. Thus the copper decomposes water and acid only in such 
quantities that the hydrogen and the azote may be in that proportion 
which is requisite to form ammonia. This instance of electro-chemical 
decomposition in definite proportions we made known several years since. 
The deutoxide, by its action on the solution of the nitrate, is so far 
the cause of the electric current established in the system, that the same 
effect may be produced by putting things in the state in which they are 
subsequently to this action. We take two porcelain capsules, one of which 
is filled with a saturated solution of nitrate of copper, and the other with 
the same solution and an addition of water. The communication be- 
tween them is established by means ‘of a cotton wick, and the end of a 
plate of copper is plunged into each of the vessels. This apparatus 
is the same as that of the tube when the deutoxide of copper has 
begun to combine with part of the acid of the nitrate ; since, in the 
one ease as well as in the other, the two ends of the plate are plunged 
into solutions of nitrate of copper possessing different degrees of con- 
centration. Now, as in both cases the electrical effects are the same, 
the explanation we have given is necessarily exact. The foregoing facts 
enable us to modify, at pleasure, the intensity of the small piles em- 
ployed to bring into action the mutual affinities in bodies. In fact, a 
plate of copper immersed in two solutions of nitrate of copper, of which 
one is and the other is not saturated, will constitute a pile. It follows 
from this, that, if the solution which is not saturated be more or less 
diluted by the addition of water, we shall have electro-chemical actions of 
greater or less energy ; and, as the solution may be progressively diluted, 
those actions will be increased or diminished in the same proportion. 
It is thus that we may obtain the different oxides of a metal in a cry- 
stallized state and distinguish the proximate principles in organic com- 
pounds. 
Lead.—In order to obtain the crystallized protoxide of lead, we take 
a glass tube measuring some millimetres in diameter, and closing it at 
one end, place at the bottom some pulverized litharge about a centi- 
metre* high. We then pour over it a slightly diluted solution of sub- 
acetate of lead, and plunge into it a plate of lead which is equally in 
contact with the litharge. The tube is then hermetically sealed. The 
surface of the plate becomes gradually covered with small prismatic-nee- 
dles of hydrate of lead; occasionally there is to be seen reduced lead ; 
and lastly, but rather rarely, a deposit of very clear dodecahedral ery- 
stals of protoxide with pentagonal faces, which lose their transparence 
* A centimetre is about 3, of an inch. 
