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 0°94 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 crystallize. 
The erystals 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 sufficiently 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 sulphurets 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 
slowly and for a long time. We shall now notice in succession the se- 
veral sulphurets which we have prepared. 
Sulphuret of Silver—A saturated solution of nitrate of silver is 
poured into one branch of the bent tube, and into the other a so- 
