of the magnetical Pyrites r &c. 341 
purpose of preparing the phosphorus bottles ; and the propensity 
to vitriolization, observed in many of the half-roasted sulphureous 
ores, appears to me to arise from this cause, rather than from 
the mere diminution of the original proportion of sulphur, or the 
actual immediate conversion of part of it into sulphuric acid ; 
nevertheless, I offer this opinion, at present, only as a probable 
conjecture, which may be investigated by future experiments 
and observations. 
The magnetical properties of the sulphuret of iron which 
forms the principal subject of this Paper, must be regarded as a 
remarkable fact ; for I have not found, in the various publica- 
tions on magnetism which I have had the means of consulting, 
even the most remote hint, that iron when combined 'with 
sulphur, is possessed of the power of receiving and retaining the 
magnetic fluid; and, judging by the properties of common 
pyrites, we might have supposed that sulphur annihilated this 
power in iron, as indeed seems to have been the opinion of 
mineralogists, who have never enumerated magnetical attrac- 
tion amongst the physical properties of those bodies ; and, 
although Werner, Widenmann, Emmerling, and Brochant, 
have arranged the magnetical pyrites with the sulphurets of 
iron, yet the magnetical property could not with certainty be 
stated as inherent in the sulphuret, for, at that time, this sub- 
stance had not been subjected to a regular chemical analysis, 
and the magnetical property might therefore be suspected to 
arise from interspersed particles of the common magnetical iron 
ore. This probably has been the opinion of the Abb£ Hauy; 
for, in his extensive Treatise on Mineralogy lately published, I 
cannot find any mention made of the magnetical pyrites, either 
amongst the sulphurets or amongst the other ores of iron.. 
