on certain stony and metalline Substance s, See. 189 
excess of ammonia; In this case, evaporation, of course, pre- 
cipitates the nickel in the state of oxide, which is of a whitish 
green colour. 
The nickel cannot be precipitated from a perfectly formed 
triple salt, by any reagent I have tried, except by a prussiate, 
or a hydrogenized sulphuret of ammonia. Potash and lime, 
as well as, I presume, other bodies, standing in the order of 
affinities before ammonia, decompose the salt ; but the nickel is 
then continued in solution by the disengaged ammonia. 
As it may be imagined that I have occasionally met with 
copper/when I describe a violet or purple ammoniacal solution, 
it is right to observe, that to avoid this error, I have either 
reduced the liquor to a neutral state, and endeavoured, without 
success, to obtain from it a precipitate, with a solution of sul- 
phureted hydrogen gas ; or, by adding an acid to slight excess, 
and immersing a piece of iron, I have not been able to detect a 
trace of copper. These, and many other trials, when they do 
not appear to be made before the estimation of the quantities of 
nickel, have been constantly made afterwards. 
But, to return to the incrustation or coating of the stone, the 
decomposition of the nitric acid shewed the presence of matter 
at least nearly metallic, although not attractable ; and the exa- 
minations made of the liquor, from which the iron was precipi- 
tated, ascertained the presence of nickel beyond dispute. The 
difficulty of obtaining the coating of the stone, either distinct 
from matter not belonging to it, or in sufficient quantity, induced 
me to relinquish the idea of attempting to give the proportions 
of its con tituent parts. 
The stone being deprived of its covering, the shining particles 
irregularly disseminated, next demand examination I first 
