CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 431 



precipitated. Being anxious to analyse the latter product, in order to 

 know its nature, we proceeded in the following manner. We took 

 two grammes of the precipitate, after having well washed it, and di- 

 gested it in a warm solution of carbonate of soda. The precipitate, 

 when washed and dried, gave 2 grammes of carbonate of copper, con- 

 sisting of 1-70 of oxide of copper, and O'O^ of carbonic acid. The 

 oxychloride contained therefore 1*70 of oxide of copper, and 0*30 of 

 hydrochloric acid, — a proportion which represents 2 atoms of oxide of 

 copper and 1 atom of hydrochloric acid. We afterwards saturated 

 the solution with sulphuric acid, and then caused it to crj'staliize. 

 The crystals of chloride of sodium furnished the quantity of chlorine 

 contained in the substance subjected to experiment. 



The chlorides of ammonium, calcium, potassium, barium, strontium, 

 and magnesium will give, with copper, analogous products, which also 

 crystallize in regular tetrahedrons. They are all isomorphous. 



Silver, as well as lead, will also give, with the same chlorides, isomor- 

 phous combinations similar to the preceding. The double chloride of 

 potassium and tin crystallizes in prismatic needles, and this we should 

 expect, since the atomic composition of the chloride of tin is not the 

 same as that of the earthy or alkaline hydrochlorates. 



We must here notice an observation made respecting the changes 

 sometimes produced in the crystallization of double chlorides. The 

 crystal is complete at first, but when the apparatus has been a long 

 time in operation, the angles of the crystal become gradually trun- 

 cated. It would seem from that circumstance that when the particles 

 of the substance which crystallizes are not sufl[iciently abundant, the 

 force which determines the regular grouping of these particles has no 

 longer the energy requisite to complete the crystal. We have had 

 frequent occasion to make the same remark in several crystallizations 

 of products formed by the aid of electric forces emanating from a 

 single pair. 



By making use of the same apparatus we may form double sulphurets, 

 double iodides, double bromides, &c. The observations which we are 

 about to make in respect to the metallic iodides and sulphufets alone will 

 throw some light on the rest of those substances. 



On the Crystallization of Metallic Sulphurets. 



Chemistry has been hitherto unable to obtain, in the moist way, 

 the metallic sulphurets in a regular form ; but this may be accom- 

 plished by uniting the action of the affinities to that of the electric 

 forces, and so disposing the apparatus that it may be able to operate 

 dowly and for a long time. We shall now notice in succession the se- 

 veral sulphurets which we have prepared. 



Sulpliuret of Silver. — A saturated solution of nitrate of silver is 

 poured into one branch of the bent tube, and into the other a so- 



