Chap. 3.] Sparry I4cid corrodes Glafs, i? 



was depofited. This was at firft naturally attributed 

 to the acid carrying over with it part of the calcareous- 

 ftone from which it was diftilled. Upon examination, 

 however, it was found that the earth depofited in the 

 water was filiceous, and this gave rife to an opinion 

 that flint was only a compofition of this acid with wa- 

 ter. This hypothecs was foon overturned, by obferv- 

 ing that the glafs veflel in which the diftillation was 

 performed was always corroded, or in part diflblved. 

 Tn this manner it was found that the fluoric acid has 

 the firigular property of diflblvihg glafs. As only a 

 moderate heat is required for the diftillation of this 

 acid, it is now ufual to make ufe of leaden veflels for 

 that purpofe j which are not corroded by the acid. 

 The bafis of this acid is unknown, as we are not ac- 

 quainted with any fubftance which can abftract its oxy- 

 gen. 



The fluoric acid has been fuccefsfully employed to 

 make etchings on glafs, in the fame manner as nitrous 

 acid is applied to copper. It combines readily with 

 earth and alkalies, but fcarcely, if it all, acts on gold, 

 filver, lead, mercury, tin, antimony, ' bifmuth, or co- 

 balt, but it diflblves their calces. It acts directly on 

 iron and zinc, with the production of inflammable gas j 

 and it likewife diffolves copper in the metallic ftatc, 

 though lefs eafily than when calcined. 



If BORAX is diflblved to faturation in boiling wate^, 

 and the vitriolic acid srdded in fuch quantity as to be 

 perceptibly in excefs, a fubftance will rife to the fur- 

 face of the water in the form of white fcales, which is 

 proved to be a peculiar acid. Many chemifts have 

 fuppofed that this acid is an artificial product, forme4 

 by a combination of the falts made ufe of in its ma- 

 nufacture. This opinion, however, has been relin- 

 qiiifhed, fince this acid has been found to exift in a 

 VOL. II. C ftate 



