36 ESSAY III. 



less, as Mr. Scheele supposes, from the fluor acid and water, 1 

 nor does it originate in any other way but from the solution 

 of the glass. 



SECTION XIV. 



Hence the idea of the fluor acid assumes a totally 

 different form. It is true that fluor contains an acid 

 before unknown, and totally different from every other, 

 which has the singular property not only of dissolving 

 glass, but of carrying it off in the form of vapour. And 

 moreover, that this acid forms, with all the alkaline salts, 

 very peculiar neutral salts, of which the ammoniacal salt 

 arising from the precipitation (Sees. xn. and xvi.) furnishes 

 an instance. 



SECTION XV. 



I cannot leave untouched the singular property of this 

 last salt, in which the fluor acid, though in the form of a 

 perfect neutral salt, yet retains its power of dissolving glass 

 unchanged ; for, upon evaporating to dryness in a cup of 

 Misnia porcelain, the liquor of (Sec. xn.) which, by its 

 smell, showed an excess of volatile alkali, I obtained 4 drms. 



1 To this I am induced, by my own experience, to accede. In distil- 

 ling fluor with oil of vitriol, I have found the retort, as well as the 

 receiver, very much corroded. I poured the acid obtained by the process 

 into a phial furnished with a glass stopple, and observed, after some time, 

 a considerable deposition. I then poured the liquor into another phial 

 like the former ; and that it might neither, on the one hand, attack the 

 glass, nor, on the other, compose siliceous earth with the particles of 

 water, according to Mr. Scheele's hypothesis, I added highly rectified 

 spirit of wine. I saw, however, after some time, another considerable 

 deposition. This seemed also to proceed from the glass that had been 

 before dissolved, which the acid let fall in consequence of the gradual 

 combination with the spirit of wine ; otherwise we must suppose, what 

 to mo appears incredible, that the acid decomposes the spirit, attracts the 

 water, and forms the earth, CRELL, 



