430 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND 
Of Double Chlorides, Double Iodides, Double Bromides, Double 
Sulphurets, Double Cyanurets, §c. 
It was conceived that by theapplication of the principles just explained, 
it would be possible to obtain in a crystallized state some double inso- 
luble combinations, which by the ordinary processes of chemistry it 
would be difficult to produce, for want of sufficient slowness in their 
operation, and because they do not enable us to abstract, at pleasure, 
any given element of a body, or to add others. Let us first direct our 
attention to the chlorides. 
We take a tube bent into the form of the letter U, having its trans- 
verse part filled with clay moistened with water: in one of the branches 
we put nitrate of copper, in the other a solution of the chloride which it 
is proposed to subject to experiment, for instance chloride of sodium. 
The end of a slip of metal (copper, for example, ) is plunged into each 
of them, and kept there by corks. Immediately afterwards, in conse- 
quence of the reaction of the two solutions on each other, and that 
of the solution of the chloride on the copper, the end immersed in the 
solution of the nitrate becomes the negative pole of a small voltaic 
apparatus, and is covered with copper in a metallic state: the nitric 
acid and the oxygen are transferred into the positive branch, where 
both concur in the production of those chemical reactions which we are 
now about to describe. The plate of copper immersed in this branch 
tends immediately to decompose the chloride; but, in consequence of 
the voltaic action, it is oxidated at the expense of the oxygen transfer- 
red. The oxide of copper thus formed combines immediately with the 
chloride of copper and chloride of sodium; whence we obtain an oxy- 
chloride of copper and sodium. By little and little this combination is 
formed, on the positive plate, into distinct tetrahedral crystals. If it is 
desired to have crystals of two or three millimetres in size, the appa- 
ratus must be left in operation for at least a year. The success of the 
experiment depends on our preventing the mixture of the liquids con- 
tained in the branches of the tube, without impeding the transfer of 
the oxygen towards the positive pole. The nitric acid contributes not 
only to oxidize the copper but to decompose the sea salt; for there is 
found in the solution some nitrate of soda. We have said that this 
combination is effected only in proportion as the end immersed in the 
solution of sea salt is slowly oxidized; for it does not take place when 
we employ an intense electric current. The most effectual mode of 
oxidizing a metal, in electro-chemical researches, is to dispose the ap- 
paratus in such a manner that it will seize the oxygen which proceeds 
from the reduction of an oxide. 
This double oxychloride, withdrawn from the contact of the air, re- 
mains unchanged ; but as soon as it is in contact with water it is de- 
composed, the chloride of sodium being dissolved, and the oxychloride 
