VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 25y 



its action on black manganese. This semi-metallic calx, as has been proved by 

 that admirable chemist Mr. Scheele, is completely soluble only in phlogisticated 

 acids, and is precipitable from them by fixed alkalis in the form of a white calx. 

 He also found, that this manganese is also soluble in water strongly impregnated 

 with fixed air, and is also precipitable from it in the form of a white calx. 

 35 Mem. Stock, p. 96. 



If fixed air be repeatedly dissolved in, and expelled from water, it leaves each 

 time a residuum which is insoluble in water, diminishable by nitrous air, and 

 capable of supporting animal life. Hence it is evidently decomposed, the phlo- 

 giston separating from it, and gradually uniting to the common atmosphere by 

 reason of the repulsive power between it and water. Dr. Priestley indeed found, 

 that a candle would not burn in it ; but this arises only from a mixture of a small 

 quantity of fixed air not yet decomposed, of which, according to the experi- 

 ments of Mr. Cavendish, i is sufficient to extinguish a candle. 



Again, Mr. Achard has converted fixed air into air of nearly the same purity 

 as common air by passing it 5 or 6 times through melted nitre. Mem. Berlin. 

 1778. Mr. Cavallo passed it but once through melted nitre, and yet found it 

 considerably meliorated, for it was diminished by nitrous air. In this case the 

 nitrous acid attracted the phlogiston ; for it is known to become phlogisticated 

 by the fusion of nitre, so as to be expellable even by the vegetable acids. 2 N. 

 Act. Ups. 171. And aqua regia may be made by mixing nitre with marine acid. 



I shall now proceed to investigate the proportion of phlogiston and elementary 

 or respirable air in fixed air. Dr. Priestley, in the 4th volume of his Observa- 

 tions, p. 380, has satisfactorily proved, that nitrous air parts with as much phlo- 

 giston to common air, as an equal bulk of inflammable air does when fired in the 

 same proportion of common air. Now, when inflammable air unites with 

 common air, its whole weight unites to it, as it contains nothing else but pure 

 phlogiston ; since therefore nitrous air phlogisticates common air to the same de- 

 gree that inflammable air does, it parts with a quantity of phlogiston equal to the 

 weight of a volume of inflammable air similar to that of nitrous air. Now 100 

 cubic inches of inflammable air weigh 3.5 gr. ; therefore, 100 cubic inches of 

 nitrous air part with 3.5 gr. of phlogiston when they communicate their phlo- 

 giston to as much common air as will take it up. I say, that nitrous air parts 

 with as much phlogiston, because it is certain, that it does not part with the 

 whole of its phlogiston to common or dephlogisticated air, for it contains much 

 more, as already shown, and, as appears by the red colour, it constantly assumes 

 when mixed with common or dephlogisticated air, which colour belongs to the 

 nitrous acid combined with its remaining phlogiston, and not to the fixed air 

 then produced, nor to the phlogisticated air remaining, as is very evident. 

 Hence the acid, thus formed, is volatile. 4 Pr. 267. 



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