of the magnetical Pyrites , &c. 327 
professor of chemistry at Madrid, published two memoirs, in 
which he states, that there are two sulphurets of iron, the one 
being artificial, and the other natural. The first is the sulphuret 
w 7 hich is formed in laboratories, by adding sulphur to red-hot 
iron, or by exposing both of them to heat in a retort. This is 
distinguished from the second sulphuret, (which is the common 
martial pyrites,) by its easy solubility in acids, especially in 
muriatic acid, by the formation of sulphuretted hydrogen gas 
during the solution of the sulphuret in the last named acid, by 
its colour, and by its inferior density. 
According to Mr. Proust, the first or artificial sulphuret is 
composed of 60 parts of sulphur, combined with 100 parts of 
iron; whilst the second sulphuret, or common pyrites, consists 
of go parts of sulphur and 100 of iron. 
He moreover observes, that the sulphur of the first sulphuret 
is difficultly separated ; but that the excess which is in the second 
sulphuret, or common pyrites, is easily expelled, and is that 
portion which is obtained by distillation, the residuum being 
then reduced to the state of the first sulphuret.* 100 parts, 
therefore, of this substance, are composed of 62.50 of iron and 
37.50 of sulphur; and, 100 parts of common pyrites are, ac- 
cording to this statement, composed of 52.64 of iron and 47.36 
of sulphur. 
These proportions, Mr. Proust considers as the, minimum 
and maximum of the sulphurets of iron. For the latter, he allows 
* Journal de Physique, Tome LIII. p. 89, and Tome LIV. p. 89. From pp. 
91 and 92 of Tome LIV. it is evident, that the author does not mean to assert, that 
the first sulphuret contains 60 per cent, of sulphur; but that 100 parts of iron are 
combined with 60 of sulphur, and form 160 of the sulphuret. In like manner, 
when 90 of sulphur are united with 100 of iron, a substance analogous to common 
pyrites is formed, which weighs 1 90 grains or parts. 
I4DCCCI V. U U 
