SULPHATE OF MAGNEStA. 227 



different forts of lime ufed in agriculture, feem to ftand, in a 

 great meafure, independent of local dnd contingent circum- 

 ftances, afid may be fafely recorded amonwft the certainties of 

 the fcience. But in this, as in other fubjccls wemuft be care- 

 ful, that our conclusions do not wander beyond the limits which 

 our premifes warrant. Magnefia and carbonate of magnefia 

 may be inimical to vegetation : But it by no means follows from 

 the admiffion of this fact, that magnefia combined with ful- 

 phuric acid pofleffes the fame dehVuclive properties. 



I conjectured that the origin of thefe falts in coal afhes Was Origin of thefe 

 to be alcribed to the decomposition of fchiftus and pyrites, up ates * 

 both which fubftances are frequently found amongft pit coal. 



In order to form a judgment refpecling the probability of Pyrites and /lea- 

 rn y conjecture, I mixed fome pounded pyrites with ionie IJ" 'g nKe ^ and 



„ J . J , / l J r . then expofed to 



iteatite reduced to powder in the proportion of about 2 : 1 the atmofphere 

 and expofed this mixture in a crucible for about an hour and a a ff° rded fulphate 

 half to the heat of a brifk fire in a common grate. There 

 remained at the bottom of the crucible a dark red powder, 

 which was expofed to the air for a considerable time before I 

 examined it. — I threw it upon a fiitre and poured diftilled 

 water upon it, which tafted exceedingly bitter, and on fur- 

 ther examination, I found it to contain fulphate of magnefia. 

 Pruffiate of potafli did not betray the leaft trace of iron held in 

 folution. Whether the magnefian fait was in a ftate of ful- 

 phite at firft I cannot tell. 



In places where fteatite and pyrites are plentiful, this procefs This artificial 

 for obtaining fulphate of magnefia would be neither difficult ^^JJiZ? 

 nor expenfive.-*In the cafe which Dr. Bollock records, might fitable. 

 there not have been fome coal afhes mixed with the clay ufed 

 for making the brick, on which he difcovered the faline efflo- 

 refcence ? 



As I have never feen the foregoing facts noticed by any per* 

 fon, I have been induced to tranfmit an account of them to 

 you. If you think them worthy to be recorded, they are at 

 your fervice. 



I am, 

 SIR, 



Your obedient humble fervant, 



WILLIAM GREGOR. 

 Creed, near Grampound, Cornwall, 

 July 6th, 1803. 



Q2 II. The 



