CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 429 



solution when it is no longer saturated. The perfect crystallization of 

 the sulphur is partly owing to the power which the alcohol possesses of 

 dissolving a certain quantity. 



The solutions of the sulphurets of barium and strontium being exposed, 

 like the preceding solutions, to the action of the positive pole, produce, 

 after some few moments, a deposit of sulphur and quadrilateral prisms 

 (which are nearly regular and unalterable in the air), of hyposulphate 

 of barytes or strontia. By continuing the operation these crystals are 

 decomposed. 



So great is the tendency of the ^irotosulphurets of barium and stron- 

 tium to undergo a change into hyposulphates, that when a plate of lead 

 or copper is substituted for one of platina, we still have a hyposulphate, 

 and only a small quantity of sulphuret of lead or copper deposited. 



If we operate Avith a solution of persulphuret of barium, we shall 

 have a precipitation of suljihur in the form of small tubercles, and a 

 formation of hyposulphate. Hence it would seem that the sulphur and 

 barium are contained in the protosulphuret in the proportions required 

 for the oxygen arising from the decomposition of the water, and trans- 

 ferred to the positive pole, to be so divided between the two elements as 

 to form the hyposulphate. All the superfluous sulphur contained in 

 the persulphuret, being unable to enter into the combination, is neces- 

 sarily abandoned, and, as it acts the part of an electro-negative element, 

 is naturally carried to the positive pole. 



It is perfectly obvious that all the chemical actions which give birth 

 to these compounds can take place only under certain electric influ- 

 ences of small energy ; for if we operate with an apparatus the action 

 of which is too powerful, we isolate all the elements, and no combina- 

 tion is possible. The whole art consists then in disposing the appa- 

 ratus in such a manner as to prevent the transfer of certain elements, 

 and thus force them into combination with other elements which are 

 conveyed to them by means of the electric currents. This new mode 

 of producing combinations is fruitful in the variety of its applications, 

 and promises results of great importance to chemistry. 



In the foregoing experiments the sulphuret was submitted to the 

 action of the positive pole : let us now see what will be the result when 

 it is in communication with the negative pole. We will take the sul- 

 phuret of barium : in this case the hydrogen reacts upon this com- 

 pound ; whence there arises a sulphohydrate of barytes, as will be sa- 

 tisfactorily proved if we test the solution. 



If it be desired to obtain this substance in a crystallized state, we must 

 add to the solution one half its Ijulk of alcohol: as it does not dissolve in 

 this liquid, it Ijecomes crystallized in considerable quantity on the plate 

 o{ platina as fast as it is formed. If we dissolve these crystals, we find 

 again all the characteristics of the sulphohydrate of barytes. 

 2 G 2 



