1 66 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



was vitriolic acid air, and no part of it inflammable" 

 (Experiments on Air, II. 16-20). 



On account of its methods of preparation, Priestley con- 

 cluded that the volatile sulphurous acid was a"phlogisticated," 

 or reduced, oil of vitriol. 



Priestley describes the properties of vitriolic acid 

 air. Priestley found that " vitriolic acid air," prepared by 

 the action of heat on a mixture of mercury and oil of vitriol, 

 resembled closely the " marine acid air " which he had 

 prepared from muriatic acid by the action of heat alone. 

 Both gases were intensely soluble in water, 1 and each con- 

 densed to a white salt when mixed with the " alkaline air " 

 ammonia. The solution of " vitriolic acid air " in water was, 

 however, only weakly acid and the gas could be expelled by 

 gentle heat, or merely by exposure to the air ; in these 

 respects the properties of the solution were in marked con- 

 trast with those of muriatic acid and of oil of vitriol. 

 Priestley calls attention to this contrast as follows : 



" Water being admitted to the vitriolic acid air absorbed 

 it about as readily as the marine acid air ; and by its union 

 with it must have formed the volatile or sulphureous acid of 

 vitriol" (ibid. p. 7). 



"Water impregnated with marine acid air is, in all 

 respects, the very same thing with the common spirit of 

 salt, except that this acid may be made considerably 

 stronger in this manner than any spirit of salt made in 

 the common way, and that it has generally less colour. 

 But water impregnated with vitriolic acid air differs 

 most remarkably from oil of vitriol. Its acidity is now 

 become trifling to what it was ; and from being the most 

 fixed, and the strongest, it is now become the weakest, and 

 the most volatile of all acids ; the smell of it being intolerably 

 pungent, and almost the whole of it evaporating when it is 

 exposed to the open air" (Experiments on Air, 1777, 

 III. 272). 



1 " Water absorbs about 20 times its bulk of this gas at a mean tem- 

 perature, according to my experience " (Dalton, Ntw System, II. 389). 



