Hydrogen from the Anode. 275 



Two experiments gave the following results : — 



Hydrogen. Sulphate of Hydrogen. 



Found. magnesia. Calculated. 



399 0-209 39-06 



25-9 0-132 24-7 



According to this, the quantity of sulphate of magnesia was 

 equivalent to the hydrogen evolved; that is to say, p-\-x=p, 

 and consequently x — 0. The black precipitate was therefore 

 not produced by the action of the current, but by a purely che- 

 mical process. 



The black incrustation nevertheless required the agency of the 

 current for its formation. A bright magnesium wire, when 

 placed in distilled water, is but feebly attacked; some hydrogen 

 is developed, and a thin film of hydrate of magnesia covers the 

 wire, protecting it from further change. It was not noticed that 

 this oxidation is preceded by the formation of the suboxide. If 

 the part not immersed be touched by a platinum wire, which 

 likewise dips into the acid, the magnesium then becomes black; 

 on stopping the current the incrustation dissolves. In a solu- 

 tion of chloride of sodium a magnesium wire long retained its 

 metallic lustre ; when touched with a platinum wire, as above 

 described, it turns immediately black. Moreover, even without 

 the use of platinum, black spots form on the wire, whence a 

 black incrustation soon spreads over its entire surface. A copious 

 quantity of hydrogen is now evolved from it.* The first black 

 spot is due to local currents arising from small inequalities of the 

 surface: as soon as the first spot is formed, local currents of greater 

 intensity are produced. But these currents do not, any more 

 than that of the battery, decompose the water, but the salt in the 

 solution; the part, therefore, which the current plays in the 

 formation of the suboxide is no other than that of continually 

 exposing fresh metallic surfaces to*the action of the water. 



The several phenomena which different salt solutions present 

 are now easily to be explained. In chloride of ammonium, the 

 suboxide dissolves immediately on its formation, with evolution 

 of hydrogen, because magnesia is, as a rule, soluble in ammo- 

 niacal salts. In solution of chloride of sodium it changes, with- 

 out being dissolved, into hydrate of magnesia, because chloride 

 of magnesium forms no basic salt with magnesia. On the other 

 hand, it dissolves to a certain degree, and with evolution of hy- 

 drogen, in sulphate of magnesium, because in this case a basic 

 saft is generated. This basic compound appears to be formed 

 when H_ : H + as 3 : 1 ; hence we should be able to deduce the 

 composition of this salt if that of the suboxide were known. 



Wohler and Buff ascribed the evolution of hydrogen from the 



T2 



