VOL. Xr.] PHILOSOPHICAL TRANSACTIONS. 35^ 



by the increase of the fire, leaving a caput mortuum, dry, styptick, and as hard 

 as a stone; yet a pound of this mass, before the fire press too much upon 

 it, will nearly afford by solution, &c. half a pound of tolerable crystalline 

 allum. The neighbouring soil differs little from other grounds with us, having 

 neither common salt nor nitre in it. I have industriously observed the springs 

 that are near the fire, and find none of them that give the least suspicion of sal 

 ammoniac. The water that nms from the adjacent collieries is vitriolic, giving 

 as deep a tincture with galls as Scarborough spa, and differs in nothing from 

 the ordinary waters of collieries. The other springs are of ordinary use, con- 

 taining no mineral salts in them. — But I hope you will cease to wonder, that 

 coal should produce a volatile salt by the action of fire, seeing I have gathered 

 sal ammoniac from a burning brick-kiln, where nothing but clay and coal is 

 burnt together, and I hope none will expect the volatilie salt in the sal ammo- 

 niac from common clay. The reason that first prompted me to seek this salt 

 there, was, that the smell of the kiln did somewhat resemble that of the sub- 

 terranean fire. There is also a sort of mineral called slate, which is partly coal, 

 partly alum-stone, partly marcasite, which being laid up in heaps and burnt, 

 is used for hardening the coal-ways; on these heaps, whilst burning, I have 

 often gathered both brimstone and sal ammoniac. 



As for the experiment of pouring cold water on the powdered marcasite, the 

 event was, that it produced a vitriolic water, but no heat. 



Though it may seem incredible to some, that black coal should yield so white 

 a volatile salt, yet they that know that all volatile salts whatever may be freed 

 from their foetor and intense colour, by transmuting them into a sal ammoniac 

 by the mediation of an acid, as spirit of salt, spirit of vitriol, allum, &c. and 

 then subliming them till they be white, will cease to doubt at this matter. The 

 reason of which change, I presume, is, because, though these volatile salts 

 carry over always some of the foetid oil with them while in a state of volatility, 

 yet being thus in a manner fixed, the foetid oil must necessarily by force of fire 

 rise first, leaving the subsequent compound salt or sal ammoniac without 

 smell. 



As to your inquiry concerning petrescent springs we have none near us. 

 There is indeed a cave some miles off^ from the roof of which hang large 

 lumps of petrified water, like icicles, some of them reaching down to the 

 ground like pillars; these icicles are good limestone, as I have tried. I shall 

 conclude when I have acquainted you with a spirit of sugar, of which a distiller 

 with us had a quantity; it seems to be the result of some anomalous fermenta- 

 tion, it is so strong that no man is able to smell at it in an open vessel without 



