230 ANNUAL OF SCIENTIFIC DISCOVERY. 



in the liquid, necessarily constitute themselves in the state of nitrate of po- 

 tassa. But when the two salts primitively chosen do not bring to the 

 mixture the elements of an insoluble composite, Berthollet's law ceases to 

 be applicable, and a great deal of uncertainty prevails about the composition 

 of the resulting dissolution. It is true, that in concentrating the liquid, 

 and crystallizing it, the least soluble of the four possible combinations ap- 

 pears ; but as, acting in this way, we return to Berthollet's law, we can 

 deduce no conclusion relative to what remains in the liquid before the 

 crystallization. M. Marguerite holds that in this case the four combina- 

 tions coexist, and he lays down, parallel with Berthollet's law, this prin- 

 ciple : When by the mixture of two salts, which have satisfied the law of 

 insolubility, a salt may be formed more soluble than the least soluble of 

 them, the action of water determines its formation within certain limits. 

 It is, consequently, the affinity of the dissolvent, or the force of solubility, 

 which groups the elements, according to its tendency to form a combina- 

 tion more soluble than the least soluble. 







ON THE EXTRACTION OF METALS BY MEANS OF THE BATTERY. 



In the course of his researches on the electrolysis of metallic combina- 

 tions, Professor Bunsen was led to determine the causes which most 

 influence the separation of the metal. These causes are two in number, 

 the principal of which is owing to what he calls the density of the current ; 

 the other cause dwells in the greater or less concentration of the electrolyte 

 or liquid to be decomposed. The maximum of effect is obtained with the 

 most dense fluid and the most concentrated solution. The word density, 

 applied to a force, necessarily excludes the idea of weight or volume. 

 Professor Bunsen means, by this word, the concentration to a single point 

 of the electrical undulations, in a manner analogous to the concentration 

 of luminous or calorific rays in the focus of a concave mirror. 



Let us take, for example, a charcoal crucible, in communication with 

 the positive pole of the battery, and place in it a small capsule of glazed 

 porcelain containing the liquid to be decomposed ; the space between the 

 crucible and the capsule is filled with hydrochloric acid, and the liquid of 

 the small capsule is put in communication with the battery by means of a 

 thin sheet or wire of platinum. The current is then established between 

 a large surfa.ce, the charcoal crucible, and a fine platinum wire, in which 

 it is concentrated ; the effects are added in this direction, and the fluid 

 becomes capable of overcoming affinities which have hitherto resisted 

 powerful batteries. The apparatus described is placed in a porcelain 

 crucible, which is kept warm in a sand bath. Chromium and manganium 

 are thus separated with the greater facility from their chloruretted solu- 

 tions, provided that the negative pole is very small and the saline solution 

 very concentrated ; if not, we may, at will, obtain hydrogen, peroxide or 

 protoxide of chromium, or chromoso- chromic oxide. When the galvanic 

 deposit is formed only of these oxides, it is sufficient to add solid mono- 



