20 ANALYSIS OF CORUNDUM, AND OF 



any further proof be neceflary, with regard to the caufe of 

 precipitates obtained in the manner ftated by Mr. Guyton, I 

 may add, that I have repeated his experiments, and have al- 

 ways found the precipitates to be fulphate of barytes. 

 Mr. Kirwan has The general conclufion to be drawn from the obfervations 

 miftakes^ 1 '* °^ ^ r - Ki rwan > already alluded to, is, that barytes has an af- 

 finity for lime, magnefia, and alumina, upon which earths 

 ftrontia does not feem to have any influence. But theie mis- 

 takes are to be accounted for in the fame manner as thole of 

 Mr. Guyton, viz. by fulphate of barytes being much lefs folu- 

 ble than fulphate of ftrontia, and therefore mowing the pre- 

 sence of a fmaller portion of ftilphuric acid, or, in other words, 

 being a much more delicate left for that fubitance. 

 Letter in Hi- With regard to the letter already mentioned as being in- 



cholfon's Jour- {e r ted in Nicholfon's Journal, and which drew fome reflec- 

 tions from Mr. Guyton, it is neceflary to examine as much of 

 it as may be thought objectionable, 

 aflerting that ^ The author fays, that he repeated the experiments of Mr. 

 pitate o/fiHca'is Guyton, with an alkaline folution of filica and alumina, and 

 foluble in acids, that he obtained a precipitate ; which precipitate, though con- 

 the refults of taining fl j ica was tota n y foluble in the acids. " Here," he 



analyfis with b . 



alkalis muft be fays, " the properties of the (ilex mu ft be confiderably altered, 

 fallacious. This mn ft re nder all analyfis with alkalis fufpicious ; and thews 



on what fallacious grounds the proud dominion of chemiftry 

 refts, which the has exercifed fo long, in fuch an arbitrary 

 and overbearing manner, in the mineral kingdom." This 

 Thisfaftison opinion is by no means likely to overthrow the pretentions of 

 the contrary tne crje miftry ; for the very circumftance of rendering filica folu- 

 provement in ble in the acids, is one of the difcoveries that has moll con- 

 modern analyfis. tributed to render certain, and to extend, our knowledge of 

 analyfis. No earthy fubftance is now thought fit to be fub- 

 mitted to further experiment, till a complete folution of it in 

 an acid be firft obtained ; and, when that folution cannot be 

 effected directly by the acid, it is always attempted by pre- 

 vious fufion with an alkali. This mode of rendering filica 

 foluble in acids, is no new difcovery ; it has been long known ; 

 and the analyfis of minerals has never been brought fo near to 

 truth, as fince it has become an indifpenfable condition. 

 Alumina at- I have no doubt as to the facl of a precipitate being formed, 



tra s i icaj ^ v m j x j n g together an alkaline folution of filica and alumina. 

 Alumina indeed appears to exercife an attraction, as I before 

 4 ftated, 



