33$ Mr. Hatchett’s Analysis 
iron hitherto known only as an artificial product, is also formed 
by nature; and that the composition of this last, agrees with those 
proportions of the artificial sulphuret which have been stated by 
Mr. Proust. 
But, from this sulphuret or magnetical pyrites, I have not, by 
analysis, as yet been able to discover any regular or immediate 
gradations into the common pyrites ; for the least proportion of 
sulphur in these amounted to 32.15, and the greatest proportion 
to 54.34; so that, between the magnetical and the common 
pyrites, the difference is considerable, in the proportions of their 
component substances, as well as in their physical and chemical 
properties ; whilst the difference which I have hitherto been able 
to detect in the proportions of some of the common pyrites, 
(very dissimilar in figure, lustre, colour, and hardness,) has 
only amounted to 2.19. 
Mr. Proust, in a general way, considers common pyrites to 
differ from the first sulphuret, or that composed of 60 parts of 
sulphur and 100 of iron, (=37.50 per cent.) by containing a 
farther addition of half the above quantity of sulphur, or 90 parts 
of sulphur and 100 of iron, (= 47 .36 per cent.) but this opinion 
he appears to have formed, in consequence of results obtained 
by synthetical experiments made in the dry way. Now, when 
we consider how difficult it is to regulate the high degrees of 
temperature, and what a numerous chain of alterations in the 
relative order of affinities most commonly result from alterations 
in these degrees of heat, it seems to me that we cannot rely, 
with absolute certainty, on synthetical experiments made in the 
above way, unless they are corrected, and contrasted with ana- 
lytical experiments made on the same substances. But it does 
