- 194 
By analysis, Mr. Hatchett found it to contain 
sulphur . .%. 36°50 
Metallic Iron . 65°50 
100°00 
At a temperature of 63° the Spec. Grav. was 4318. It 
has been found to agree precisely with artificial Sulphuret 
of Iron, and it is fairly concluded that its proportions are 
probably subjected to certain laws, especially during its 
formation in the humid way, always acting in an invariable 
manner: and it is also found that Iron, when naturally or 
artificially combined with 36°50 or 37 per cent. of Sulphur, 
is not only still capable of receiving the magnetic fluid, but 
is also rendered capable of retaining it, and that beyond 
45°30 or 46 percent. of Sulphur, as in common Pyrites, 
all susceptibility of the magnetic influence seems to be 
destroyed. This and other proofs of certain proportions 
of mixtures having a peculiar effect upon the magnetic 
property of Iron, stamp a great value upon these researches. 
I have a specimen showing the oxygenizement by moisture 
on the surface, having taken the impressions of the grass 
near which it lay; and I find that a fresh fracture is of a 
yellowish grey, but soon tarnishes. 
The upper figure represents part of a stratified piece, 
which shows the fresh fracture with a surface that has an 
aggregated appearance; but this does not arise from any 
mixture. 
The lower specimen, having a smoother fracture, shows it 
better, and has a tendency towards a cubic crystallization, 
which would seem to mark its relationship to common 
Pyrites, although they are nevertheless sufficiently distinct. 
The upper specimen, figured at al. 30, is nearly of the 
sort of Pyrites spoken of by Mr. Hatchett as accompanying 
this magnetical kind. It 1s also accompanied by Lapis 
Ollaris or Potstone, though not of the best sort. I find 
Yellow Copper Ore and Sulphuret of Lead attached to 
some of my specimens. 
I have some of the magnetic part of the rock from 
Wicklow in Ireland, which has a distant resemblance to 
Magnetic Pyrites, but is duller, greyish or blackish, and 
does not in common fly to the magnet so readily. 
