VOL. LXXV.] PHILOSOPHICAL TRANSACTIONS. IQ 



arise from the nitrous acid in it being phlogisticated ; and therefore I tried whether 

 nitre, much phlogisticated, would precipitate silver from its solution. For this 

 purpose I exposed some nitre to the fire, in an earthen retort, till it had yielded a 

 good deal of dephlogisticated air ; and then, having dissolved it in water, and 

 added to it some well purified spirit of nitre till it was sensibly acid, in order to 

 be certain that the alkali did not predominate, I dropped into it some solution of 

 silver, which immediately made a very copious precipitate. This solution how- 

 ever being deprived of some of its phlogiston by evaporation to dryness, and ex- 

 posure for a few weeks to the air. lost the property of precipitating silver from its 

 solution ; a proof that this property depended only on its phlogistication, and not 

 on its having absorbed sea-salt from the retort, or by any other means. Hence 

 it is certain that nitre, when much phlogisticated, is capable of making a pre- 

 cipitate with a solution of silver ; and therefore there is no reason to think that 

 the precipitate, which our salt occasioned with a solution of silver, proceeded 

 from any other cause than that of its being phlogisticated ; especially as it ap- 

 peared by the smell, both on first taking it out of the tube, and on the addition 

 of the spirit of nitre, previous to dropping in the solution of silver, that the acid 

 in it was much phlogisticated. This property of phlogisticated nitre is worth the 

 attention of chemists ; as otherwise they may sometimes be led into mistakes, in 

 investigating the presence of marine acid by a solution of silver. 



In the above-mentioned paper I said, that when nitre is detonated with char- 

 coal, the acid is converted into phlogisticated air; that is, into a substance which, 

 as far as I could perceive, possesses all the properties of the phlogisticated air of our 

 atmosphere ; from which I concluded, that phlogisticated air is nothing else than 

 nitrous acid united to phlogiston. According to this conclusion, phlogisticated 

 air ought to be reduced to nitrous acid by being deprived of its phlogiston. But 

 as dephlogisticated air is only water deprived of phlogiston, it is plain, that adding 

 dephlogisticated air to a body, is equivalent to depriving it of phlogiston, and 

 adding water to it ; and therefore phlogisticated air ought also to be reduced to 

 nitrous acid, by being made to unite to, or form a chemical combination with de- 

 phlogisticated air ; only the acid formed this way will be more dilute, than if the 

 phlogisticated air was simply deprived of phlogiston. 



This being premised, we rnay safely conclude, that in the present experiments 

 the phlogisticated air was enabled, by means of the electrical spark, to unite to, 

 or form a chemical combination with the dephlogisticated air, and was thus 

 reduced to nitrous acid, which united to the soap-lees, and formed a solution of 

 nitre; for in these experiments those two airs actually disappeared, and nitrous 

 acid was actually formed in their stead; and as moreover it has also been just 

 shown, from other circumstances, that phlogisticated air must form nitrous acid, 



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