i88 Mr. Howard's Experiments and Observations 
and digested the unattractable portion with nitric acid, which 
was presently decomposed ; but, owing to a strong adherence 
of some of the interior and earthy parts of the stone, it did not 
disentangle the coating or metalline part without some difficulty. 
The acid being sufficiently neutralized, the solution was passed- 
through a filtre, and saturated to excess with ammonia. An 
abundant precipitate of oxide of iron was produced ; and, when 
this oxide was separated, I observed the saline liquor to have a 
greenish colour. I evaporated it to dryness ; and redissolved the 
dry salt in distilled water. No precipitate was formed during 
the evaporation, nor was the colour of the solution entirely 
destroyed. It appeared to me like a triple salt, described by Mr. 
Hermstadt* as an ammoniacal nitrate of nickel. By exami- 
nation with prussiate of ammonia, it yielded a whitish precipitate, 
inclining to a violet colour ; and, by various properties, I was 
soon confirmed in the opinion, that nickel was present. Since 
I shall have occasion more than once to treat of the triple 
compound, and since it has been only mentioned by Mr. 
Hermstadt, it is necessary now to detail some of its distinctive 
characters. The same chemist informs us, that the three mineral 
acids, with ammonia, enter into similar combinations with nickel ; 
and I have observed, that oxide of nickel can be dissolved by 
nitrate and muriate of ammonia. The muriate seems to take up 
the largest quantity. The colour of this salt is by no means 
uniform: it is sometimes grass green, violet, rose colour, 
inclining to purple, and I have seen it almost colourless. It 
seems to be purple, and to incline to rose colour and violet, 
when all the oxide of nickel is not united to both acid and 
alkali, but, from the deficiency of salt, is held in solution by an 
9 Annales de Chirr ie. Tom. XXIL p. xo8? 
