2lo Experiments and Obfervations 



with prufiiate of ammonia, it yielded a whitifh precipitate, 

 inclining to a violet colour; and, by various properties, I 

 was foon confirmed in the opinion that nickel was prefent. 

 Since I Hi nil have occafion more than once to treat of the 

 triple compound, and iince it has been only mentioned by 

 Mr. Hermftadt, it is ncceflary now to detail fome of its di- 

 ilinctive characters. The fame chemift informs us, that the 

 three mineral acids, with ammonia, enter into Similar com- 

 binations with nickel; and I have obferved that oxide of 

 nickel can be diifolved by nitrate and muriate of ammonia. 

 The muriate feems to take up the larger! quantity. The co- 

 lour of this fait is by no means uniform : it is fometimes grafs 

 green, violet, rofe colour, inclining to purple, and I have feen 

 it almofi colourlefs. It feems to be purple, and to incline to 

 rofe colour and violet, when all the oxide of nickel is not 

 united to both acid and alkali, but, from the deficiency of 

 fait, is held in folution by an excefs of ammonia. In this 

 cafe, evaporation, of courfe, precipitates the nickel in the ftate 

 of oxide, which is of a whitifh green colour. 



The nickel cannot be precipitated from a perfectly formed 

 triple fait by any reagent I have tried, except by a prufiiate, 

 or a hydrogenized fulphuret of ammonia. Potaih and lime, 

 as weH as, I prefume, other bodies, Handing in the order of 

 affinities before ammonia, decompofe the fait; but the nickel 

 is then continued in folution by the difengaged ammonia. 



As it may be imagined that I have occasionally met with 

 copper, when \ defcribe a violet or purple ammoniacal folu- 

 tion, it is right to obferve, that to avoid this error, I have 

 either reduced the liquor to a neutral Hate, and endeavoured, 

 without fuccefs, to obtain from it a precipitate, with a folu- 

 tion of fulphureted hydrogen gas; or, by adding an acid to 

 flight excel?, and immerflng a piece of iron, I have not been 

 able to detect a trace of copper. Thefe, and many other 

 trials, when they do not appear to be made before the efti- 

 mation of the quantities of nickel, have been conflantly made 

 afterwards. 



But, to return to the incruftation or coating of the ftone, 

 the decomposition of the nitric acid mowed the prefence of 

 matter at lean: nearly metallic, although not attractable ; 

 and the examinations made of the liquor, from which the 

 iron was precipitated, afcertained the prefence of nickel be- 

 yond difpute. The difficulty of obtaining the coating of the 

 ftone, either diftincl from matter not belonging to it, or in 

 fufficient quantity, induced me to relinquifh the idea of at- 

 tempting to give the proportions of its conftituent parts. 



The (tone being deprived of its covering, the mining par- 

 ticles 



