oj the magnetical Pyrites , &c. 31^ 
= 13.50 per cent, but, upon examining the residuum, I found 
that only part of the sulphur had been thus separated. 
The magnetical pyrites, when digested in dilute sulphuric acid, 
is partially dissolved, with little effervescence, although there is 
a very perceptible odour of sulphuretted hydrogen. 
The solution is of a very pale green colour. 
Pure ammonia produced a dark green precipitate, tending to 
black ; and prussiate of potash formed a very pale blue preci- 
pitate, or rather a white precipitate mingled with a small portion 
of blue. The whole of the latter, however, by exposure to the 
air, gradually assumed the usual intensity of Prussian blue ; and 
the blackish green precipitate, formed by ammonia, became 
gradually ochraceous. These effects therefore fully prove, that 
the iron in the solution was, for the greater part, at the minimum 
of oxidizement, so as to form the green sulphate, and white 
prussiate, of iron ; * and, consequently, that the iron of the 
magnetical pyrites is either quite, or very nearly, in the state 
of perfect metal. 
This pyrites, when treated with nitric acid, of the specific 
gravity of 1.38, diluted with an equal quantity of water, is at 
first but little affected ; but, when heat is applied, it is dissolved, 
with much effervescence, and discharge of nitrous gas; the 
effervescence, however, is by no means so violent as when the 
common pyrites are treated in a similar manner. It is also 
worthy of notice, that if the digestion be not of too long dura- 
tion, a considerable quantity of sulphur, in substance , is separated ; 
whilst, on the contrary, scarcely any can be obtained from the 
common pyrites, when treated in a similar manner ; although I 
* Rechercbes sur le Bleu de Prusse, par M. Proust. Annales de Chitnie, 
Tome XXIII. p. 85. 
MDCCCIV. T t 
