438 M. BECQUEREL ON CHEMICAL DECOMPOSITION" AND 



Crj'stallized sulphur is also obtained !)y abandoning to the influence 

 of the air a solution of that substance in carburet of sulphur, or by 

 melting some sulphur and letting the liquid stand to cool until there is 

 formed at the surface a solid crust, which is broken in order to draw 

 oif the liquid. But the process which we have described is different 

 from the two preceding processes, and bears some analogy to that 

 which nature employs in some circumstances ; for instance, in the slow 

 decomposition of sulphuretted hydrogen gas and feculent matters 

 which, in the course of time, deposit well-defined crystals of sulphur. 

 In both cases the crystallization is the result of an excessively feeble 

 action, on which we shall have occasion to remark when we come to 

 treat of spontaneous actions. 



The products resulting from the decomposition of the sulpho-carbo- 

 nate of pota-sh vary according to the intensity of the electric current 

 and the degree of concentration of the solution. With an alcoholic 

 solution of sulpho-carbonate, diluted with water, we obtain but little 

 sulphur, and a great quantity of sulpho-carbonate of lead and potash. 

 These differences in the results are owing to the ratios which the affi- 

 nities of the several bodies bear to the intensities of the current, which 

 vary according to the conductibility of the liquids and the energy of 

 the chemical action which produces the current. In the present state 

 of the science, it is impossible to see a priori what should happen in 

 any proposed case ; that is to be learnt from experiment only. 



The sulpho-carbonates of the other bases submitted to the same 

 species of experiment gave analogous results. It is owing to the slow- 

 ness of their decomposition, and to the appropriate choice of metals 

 with respect to the positive pole, that we obtained the sulphate of ba- 

 rytes in crystals derived from the primitive form. 



Another Application. — We fill with a solution of bicarbonate of soda 

 a tube containing, in its lower part, clay moistened with the same so- 

 lution, and place it in another which contains a solution of sulphate of 

 copper. We then plunge into each liquid one of the extremities of a 

 plate of copper, and observe the following effects : the end which is in 

 the solution of sulphate being the negative pole decomposes this salt, 

 and attracts the copper, while the oxygen and the sulphuric acid pass 

 to the other side. But as the sulphuric acid on its passage meets with 

 carbonic acid, it expels this from the combination and takes its place. 

 The carbonic acid then forms with the oxide of copper a carbonate 

 which, by combining with that of the soda, produces a double carbonate 

 of copper and potash, which crystallizes in beautiful satin-like needles of 

 a bluish green colour. This substance, which does not dissolve in water, 

 is decomposed with the aid of heat ; the carbonate of soda is dissolved, 

 that of copper is precipitated and become brown, like the common car- 

 bonate when subjected to the action of boiling water. 



In the preceding experiments, the power of sulphuric acid in expelling 



