Ei-FLOkESdENCES £)F WALLS. ] 13 



Ih atyzlyfing the clay I proceeded nearly upon the plan Ahalyf^sofihe 

 Jjointed out by M. Vauquelin in the 30th vol. of the Ann. cl»y> *«• 

 de Chimie. 



This operation is however fo tedious^ and requires fo much 

 nicety in the management, that I made fome attempts to af- 

 certain theexiftence of magnefia in the clay by a fliorter pro- 

 cefs. The firfl method vrhich I employed was fuggefled by 

 an obfervation of Mr. Kirwan ; he Rates that alumine is fuf- 

 ficiently difcriminated from magnefia by the greater foiubility of 

 the latter in dilute fulphuric acid; but it appears that Ihedif- 

 ference of folubility of thefe two fubftances cannot be em- 

 ployed as a teft of the prefence of magnefia where it exifts 

 only in fmall proportion ; for I found that the fulphuric acid 

 diluted with above 200 times its weight of water, after being 

 in contaa with pure alumine for the fpaceof 10 minutes only* 

 had acted upon the alumine fo far that a precipitate was 

 formed in the fluid by the addition of ammoniac. 



The acetous acid is flated as pofleffing a much more power- 

 ful a<5tion over magnefia than over alumine; but upon trial 

 the fame objedion occurred againft its ufe as in the former 

 Inilance. 



The property which the rhagnefian falts po{fefs of being 

 decompofed by pure ammoniac but not by the carbonate of 

 ammoniac, feemed to offer a method by which the fulphates 

 of magnefia and of alumine might be feparated when mixed 

 together in folution, and by which means confequently tl|||^ *' 



prefence of magnefia might be detefted in the clay under 

 examination. But I found that though the fulphate of mag- 

 nefia alone is not decompofed by the carbonate of ammoniac, 

 yet that when a mixed folution ofalu^i and the fulphate of 

 magnefia is fubjeded to the aftion of the carbonate of ammo- 

 niac, both the alumine and the magnefia are precipitated, fo 

 that when the fluid is feparated by filtration, the addition of ' ~ 

 pure ammoniac produces no farther etfe6l : 



After I had made the unfuccefsful experiment related above 

 refpefting the formation of the fulphuric acid, I received the 

 lafl number of your Journal^ containing a communication from 

 Mr. Gregor, in which he gives an account of the produflion 

 of the fulphate of magnefia from the afiies of pit-coal. He jvfr.cJregor^set- 

 attributes the produ^ion of this fait to the decompofition of pe"menr no» ap* 

 the fchiftus and pyrites which are commonly found in coal, f^f^f^ ^"eftioji. 



Voi. VI.-^G-CIOBSR, 1803. I JindascoallSier 



iNteie not mMo 



