1 822.] Method of analyzing the Ores of Nickel. 211 



A solution of arseniate of iron and nickel, saturated with an 

 alkali even to the commencement of precipitation, and after- 

 wards mixed with a solution of acetate of lead, precipitates arse- 

 niate of lead and arseniate of iron, until no more remains in the 

 liquid. This circumstance arises from the affinity of the arsenic 

 acid being so much greater for the oxide of lead than that of 

 the acetic acid, that it forms a subarseniate of lead in the liquid 

 which contains acetic acid in excess. The subarseniate of iron 

 not being soluble in it precipitates at the same time ; for the 

 strongest acids combine with the oxide of lead, and the acetic 

 acid is at length the only free acid in the liquid. The solution 

 which contains the oxides of nickel and lead; when mixed with 

 sulphate of soda, suffers the greater part, but not the whole, of 

 the oxide of lead added in excess to separate. If excess of 

 ammonia be afterwards added, a greyish precipitate is formed 

 composed of oxide of lead and oxide of nickel. In order to 

 separate the last remains of the lead, sulphuretted hydrogen 

 must be employed. 



Hydrosulphuret of ammonia does not separate arsenic acid 

 from oxide of nickel ; for the precipitate produced is as soluble 

 in an excess of hydrosulphuret as in caustic ammonia. The 

 -solution has a very deep yellowish-brown colour : when rather 

 concentrated, it loses its transparency. Acids decompose it, 

 but the precipitate contains some arsenic, and usually a small 

 quantity of sulphuret of nickel is redissolved by the acid, even 

 when it is only the acetic. If an ammoniacal solution of this sul- 

 phuret, which contains arsenic acid, be evaporated, a part of the 

 sulphuret is deposited in the form of arseniuretted sulphuret of 

 nickel (that is to say, a compound of sulphuret and of arseniuret 

 of nickel), and another part oxidizes in proportion as the ammo- 

 nia evaporates, and gives rise to a solution of nickel. The sul- 

 phuretted arseniuret of nickel is insoluble both in muriatic acid 

 and in ammonia. Cobalt differs from nickel in being perfectly 

 well precipitated by the hydrosulphurets, without" being redis- 

 solved by an excess of them. 



Oxide of Nickel and other Salifiable Bases.— It is well known 

 that oxide of nickel dissolves completely in ammonia.. This, 

 solution ought to be considered as forming a double &ubsalt ;. 

 yet the hydrate of nickel is soluble in ammonia, although in a 

 quantity much smaller than the oxide combines with, an acid* 

 The same affinity that determines the solubility of oxide of 

 nickel in ammonia exists between it and other bases, although 

 the combinations with these latter are insoluble in water. 

 Consequently when a solution of nickel is mixed with ai^other of 

 an insoluble base, the ammonia occasions a precipitate, which 

 contains nickel, and from which an excess of ammonia cannot 

 separate this metal. 



In this case the oxide of nickel is divided between the two 



p2 



