546 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



2. The smallest portion of vitriolic acid added to this water occasioned an im- 

 mediate and copious precipitation ; and when this acrid water was diluted with 

 200 times its bulk, of pure water, the precipitation on the addition of vitriolic 

 acid was yet sufficiently obvious. 3. A single drop of this acrid water, added to 

 solutions of tartar of vitriol, Glauber's salt, vitriolic ammoniac, alum, Epsom 

 salt, selenite, occasioned an immediate precipitation in all of them. 



f. The precipitate thrown down by the caustic vegetable alkali (d, 3,) was put 

 into water, in expectation that it would make lime-water; but neither on stand- 

 ing, nor after boiling, did this water exhibit any precipitation when concentrated 

 vitriolic acid was dropped in it; nor had it any acrimonious or other peculiar 

 taste. 



g. Concentrated vitriolic acid was added to one portion of the precipitate d 3; 

 concentrated nitrous acid to a 2d portion ; and marine acid to a 3d portion. No 

 effervescence could be observed, nor was there any appearance of solution. 

 After standing 1 hour water was added ; and the acids thus diluted were suffered 

 to remain on the portions of the precipitate for another hour. They were then 

 decanted, and saturated with mild fossil fixed alkali, but without any appearance 

 of precipitation. 



h. The part precipitated by the phlogisticated alkali, when mixed with nitre 

 and borax, and fluxed by a blow-pipe on charcoal, formed a black, glass ; on flint- 

 glass, a white ; and on a tobacco pipe an opaque yellowish white one. 2. 

 Another portion melted with soap and borax in a crucible, formed a black glass, 

 but without any metallic appearance. 



i. The insoluble residuum A was boiled in water, the water decanted, and 

 mild fixed alkali added, but without any subsequent precipitation. 2. This in- 

 soluble powder was not attacked by the nitrous or marine acids ; but being put 

 into vitriolic acid, and boiled a considerable time till the acid became highly con- 

 centrated, it dissolved entirely, and separated again on the addition of water. 

 It will appear in the sequel, that the same thing happens to marmor metallicum, 

 when dissolved by boiling in the acid of vitriol. 



Hence it appears, that 100 parts of this spar contain, terra ponderosa pura 

 78.6, marmor metallicum 0.6, fixed air 20.8. 



Observations. — 1st. The quantity of mild fixed alkali necessary to saturate an 

 acid, previously united to the terra ponderosa, contains more fixed air than is 

 necessary to saturate that quantity of terra ponderosa d 1, 2. 2dly. The terra 

 ponderosa, when precipitated from an acid by means of a mild fixed alkali 

 (d 1, 2,) readily burns to lime; and this lime-water proves a very nice test of 

 the presence of vitriolic acid, e 2, 3. 3dly. It is very remarkable, that the 

 terra ponderosa spar, in its native state, will not burn to lime. In the lower 

 degrees of heat it suffers no change, as before observed, besides the loss of its 



