A Chemical Analyfii of Three Species of Whin/lone, and Two of Lava. 44* 



T)f Edinburgh. A portion of it being reduced to minute grains, of fuch a Cze as the par- 

 ticles of the ftone feemed to have confided 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 nitrate 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 paffed through was 

 evaporated to drynefs. A faline matter remained, which being mixed with fome charcoal, 

 and heated, deflagrated like nitrous falts. Having waihed the coaly refiduum, and evapo- 

 rated the water, I got fome perfeftly pure carbonate of foda. There had been, therefore, 

 in the fandftone, fome common fait, which, by this procefs, was decompofed, and its acid 

 and alkali collected feparately ; but whether the whole of the fait was obtained, and what 

 proportion it bore to the earthy parts, I cannot determine, as the ftone itfelf was not 

 analyzed. 



The next fpecimen was taken from a ftratum of fandftone, which lies below the hill of 

 Salifbury Craig; and I chofe this fpecies, becaufe the whin to which it is contiguous has 

 already been fliown to contain foda. Some of it being reduced to the ftate of fine fand, 

 and treated in every refpe£l as the preceding, gave a portion of muriate of filver, and of 

 carbonate of foda. The exiftence, therefore, of fea- fait in thefe varieties of fandftone, is 

 thus fully eftabliflied ». 



The celebrated Mr. Klaproth of Berlin has already fliown, that pot-afh enters into the 

 compofition of feveral ftony fubftances ; and by the experiments defcribed in this paper, 

 the other fixed alkali, foda, has alfo been proved to exift in mineral bodies, as it has been 

 feparated from nine different varieties; all of which alfo contain a certain quantity of 

 muriatic acid. 



As cauftic fixed alkali was much ufed in thefe analyfes, I fliall conclude this paper by 

 defcribing, in a few words, the method by which I prepare it ; both becaufe its purity is 

 of the greateft importance, and becaufe the procefs I employ differs, in fome circum- 

 ftances, from that of moft chemifts. Having obtained an alkali free from all earthy mat- 

 ter, either by burning white tartar, or by repeated folutions and cryftallizations of carbo- 

 nate of foda, I diffolve it in a confiderable quantity of water. The requifite proportion of 

 lime being flacked, and allowed to cool, it is diluted with water, and then mixed with the 

 folution of the alkali. This mixture is frequently ftirred during two or three days; for 

 when no heat is applied, the lime requires a certain time to attraft the whole of the car- 

 bonic acid. In the next place, the mixture is filtered through a piece of linen placed in a 

 funnel, and water poured on it till the whole of the alkali is waihed out. As it paffes 

 through, it is poured, at intervals, from the bottle which receives it firft, into a fecond 

 that is clofely ftopped. 



• Since thefe experiments were performed, I have feen feverat decompofed fandftones, on the furfaces of 

 which there was an efflorefcence of common fait, 



Vol. IV. — January 1801, * 3L In 



