C 1 53] 



hy all the chemical methods that are in ufe j but 

 could not find that water thus impregnated con- 

 tained the leaft perceivable quantity of the acid. 



Mr. Hey, indeed, who affifted me in this exami- 

 nation, found that diftilled water, impregnated with 

 fixed air, did not mix fo readily with foap as the di- 

 ftilled water itfelf ; but this was alfo the cafe when 

 the fixed air had palled through a long glafs tube 

 filled with alkaline falts, which, it may be fuppofed, 

 would have imbibed any of the oil of vitriol that 

 might have been contained in that air *. 



It is not improbable but that fixed air itfelf may 

 be of the nature of an acid, though of a weak and 

 peculiar fort. Mr. Bergman of Upfal, who honoured 

 nie with a letter upon the fubjecl, calls it the aerial 

 acid, and, among other experiments to prove it to be 

 an acid, he fays that it changes the blue juice of 

 tournefole into red. 



The heat of boiling water will expel 1 all the fixed 

 air, if a phial containing the impregnated water be 

 held in it; but it will often require above half an 

 hour to do it completely. 



Dr. Percival, who is particularly attentive to every 

 improvement in the medical art, and who has 

 thought fo well of this impregnation as to prefcribe 

 it in feveral cafes, informs me that it feems to be 

 much ftronger, and fparkles more, like the true 

 Pyrmont water, after it has been kept fome time. 

 This circumftance, however, {hews that, in time, the 

 fixed air is more eafily difengaged from the water, and 



* An account of Mr. Hey's experiments will be found in the 

 Appendix to thefe papers. 



Vol. LXII. X though, 



