430 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND 



Of Double Chlorides, Double Iodides, Double Bromides, Double 

 Sidjjhurets, Double Cyanurets, S^c. 



Itwas conceived that by the application 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. 

 Tlie 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 



