Of WHINSTONE and LAVA. 95 



da ; and will even render it probable, that this alkali is widely 

 difFufed through mineral bodies. 



Soon after I firfl difcovered it in whins, and had communi- 

 cated the circumftance to Sir James Hall, he fent me, from a 

 high fandflone rock in his eflate, a quantity of the ftone decom- 

 pofed ; and informed me that there was a faline efflorefcence 

 mixed with it, which was collected along with the loofe matter, 

 and which feemed, by the taite, to be fea-falt. The place has 

 been long called by the common people the Salt Heugb. By lim- 

 ply boiling fome of the decompofed fandy part in water, and 

 afterwards filtering and evaporating the water, I obtained regu- 

 lar cryflals of fea-falt, mixed with a fmall quantity of fulphate 

 of foda. 



Hence it appeared likely, that common fait would be found 

 to be one of the component parts of ordinary fandflone flrata. 

 To verify this important obfervation, I next examined two hard 

 and folid fpecimens, taken from fome depth below the furface, 

 and perfectly free from decompofition. The firfl was broken from 

 a quarry about two miles to the weflward of Edinburgh. A por- 

 tion of it being reduced to minute grains, of fuch a fize as the 

 particles of the flone feemed to have eonfifled of originally, was 

 mixed with fome diluted nitric acid, and boiled with it gently for 

 three hours. The acid, after being filtered, was examined with ni- 

 trate of barytes, with which it produced only a flight cloud. 

 But nitrate of filver, when poured into it, threw down a copious- 

 white precipitate of muriate of filver, indicating the prefence of 

 muriatic acid. 



After this precipitate was feparated by filtration, the liquor 

 which palled through was evaporated to drynefs. A faline 

 matter remained, which being mixed with fome charcoal, 

 and heated, deflagrated like nitrous falts. Having wafhed the 

 coaly refiduum, and evaporated the water, I got fome perfectly 

 pure carbonate of foda. There had been, therefore, in the fand- 

 flone 



