i g& Mr. Howard's 'Experiments and Observations 
infer, that 100 grains of pure iron acquires, by such a process, 
45 grains of oxygen ; and that, whenever a metallic substance, 
supposed to be iron, does not, under the same circumstances, 
acquire the same proportionate weight, something is either 
volatilized, or left in solution. Hence, when a metallic alloy of 
nickel and iron presents itself, a judgment may, at least, be 
formed of the quantity of nickel, by the deficiency of weight in 
the precipitated oxide of iron. 
This mode of treatment was not allowed me in the examina- 
tion of the coating of the stone, because it was impossible to 
know in what state of oxidizement the iron existed. But, as the 
particles disseminated through the whole mass, are clearly 
metallic, a very tolerable idea of the quantities of nickel con- 
tained in them will be obtained, by noting the quantity of oxide 
of iron separated, as above described. 25 grains of these metallic 
particles were therefore heated with a quantity of nitric acid, 
much more than sufficient to dissolve the whole. Some earthy 
matter, which, as in a former case, was not separable by me- 
\ 
chanical means, remained after a complete solution of the metal 
had been effected. This earthy matter, after being ignited, weighed 
two grains. The real matter of the present examination, was 
therefore reduced to 23 grains, and was in complete solution. I 
added ammonia to a very sensible excess. The oxide of iron 
was thereby precipitated, and, being collected and ignited, it 
weighed 24 grains; whereas, according to my experiments, 
33 g ra * ns should have been produced from the solution, had it 
contained nothing but iron. I examined the saline liquor, when 
free from ferruginous particles, and discovered it to be the triple 
salt of nickel. Hence, allowing for loss, the quantity of nickel 
may be estimated, by calculating the quantity of iron contained 
