of WHINS TONE ami LAFJ. 83 



in thefe (tones ; and their conlGderable fufibility favoured the 

 fufpicion. 



Soon after thefe analyfes were made, I obferved another cir- 

 cumftance, which amounted to an abfokite proof of the whins 

 containing fomething of a faline nature, in combination with 

 their earthy bafes. Moft of the artificial cryftaUites, made by 

 Sir James Hall, which I had always an opportunity of exa- 

 mining, threw out on their furfaces, two or three weeks after 

 their formation, a white efflorefcence, which had a very fait 

 tafte. It was in too fmall quantity to be colletfled and exami- 

 ned ; but when waflied off, it was often formed a fecond time. 



I WAS thus convinced of the exiftence of fome faline fub- 

 ftance in thefe bodies, and made different experiments with fe- 

 veral of them, in order to feparate it, and afcertain its nature ; 

 and foon found that it was foda. 



I SHALL next defcribe fome of the methods by which this al- 

 kali was moft eafily feparated from the earthy parts of the 

 whins. 



Experiments to obtain the Soda, atid determine its ^lantity. 



Having brokeri fome of the bafalt of Staffa to fmall frag- 

 ments, I weighed 400 grains, and ground the whole with water 

 to an extremely fine powder, in a Wedgwood mortar. The 

 powder, and the water with which it had been ground, were 

 "then put into a fmall retort, and mixed with about 1 200 grains 

 of fulphuric acid, which I had carefully diftilled for this ope- 

 ration. I placed the retort in the fand bath of a fmall furnace 

 which I ufe for analyfes, adapted a receiver, raifed the fire till 

 the acid began to diftill floWly, and carried on the diftillation 

 to drynefs. Water was then poured into the retort, and boiled, 

 the mixture thrown on a filter, and the Undiffolved refiduum 

 fufficiently waflied. This refiduum was njxt treated a fecond 



time 



