212 M, Berzelius on the [Matich, 



bases, towards which it usually acts as an acid or electro-nega- 

 tive body. It is in this manner that it precipitates with the 

 alkaline eartlis, the protoxide of iron, of manganese, lead, &,c. 

 But with the protoxide of iron and with alumina, it precipitates 

 in the state of base or of electro-positive body, and on this 

 account, th^se latter contain much less than the former. If the 

 oxide of nickel contains small quantities of another base, it is 

 very frequently difficult to discover what this base is. Barytes, 

 strontian, and lime, are shown when a concentrated solution of 

 the oxide is mixed with carbonate or sulphate of ammonia, which 



frecipitate the earths, and form soluble salts with the oxide* 

 ^hosphate of ammonia cannot be employed to separate it from 

 magnesia ; for though phosphate of nickel is soluble in all pro- 

 portions in ammonia, it precipitates nevertheless with phosphate 

 of magnesia, without the possibility of separating it by ammonia 

 added even in great excess. I know of no other method of 

 separating them, than that of precipitating the oxide of nickel 

 from the mixed solution by hydrosulphuret of ammonia, and of 

 immediately decomposing the excess of the hydrosulphuret by 

 a few drops of acetic acid, and filtering the solution. The mag-- 

 nesia remains in the solution, and may be separated from it in 

 the usual manner ; but in general, different methods must be 

 followed with every base with which the oxide of nickel may be 

 mixed. 



It follows from what has been mentioned, that the solubility 

 of oxide of nickel in ammonia cannot be employed to separate 

 it perfectly from foreign admixtures insoluble in this alkali ; for 

 the parts undissolved or precipitated always contain more or 

 less oxide of nickel. 



The combination of oxide of nickel with caustic potash 

 appears to me to be the most remarkable of all those which it 

 forms with salifiable bases. When a solution of caustic potash 

 is gradually added to one of nickel supersaturated with ammonia, 

 a whitish precipitate appears, which redissolves, but which is 

 eventually reproduced, and does not again disappear. When 

 the potash ceases to render the liquor turbid, it becomes colour- 

 less, and a greenish sediment is slowly deposited. On this 

 occasion, the oxide of nickel combines with the potash, and 

 becomes insoluble. The redissolving of the first formed portions 

 of the precipitate is derived from their decomposition by the 

 ammoniacal salts ; but at the moment in which the latter are 

 decomposed, the precipitate remains undissolved. The preci- 

 pitate is insoluble in ammonia. Separated by the filter, it forms 

 a gelatinous mass, which it is extremely difficult to wash. If 

 there is any lime in the liquid, the precipitate is less coherent, 

 and more easy to wash ; but it then contains all the lime remain- 

 ing in the solution. Boiling water penetrates the niccolale of 

 potash (sit tenia verbo) much better ; but it also decomposes it 



