512 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



Mr. Kirwan allows that lime-water is not rendered cloudy by the mixture of 

 nitrous and common air; but contends that this does not prove that fixed air is 

 not generated by the union, as he thinks it may be absorbed by the nitrous sele- 

 nite produced by the union of the nitrous acid with the lime. This induced me 

 to try how small a quantity of fixed air would be perceived in this experiment. 

 I accordingly repeated it in the same manner as described in my paper, except 

 that I purposely added a little fixed air to the common air, and found that when 

 this addition was -^ of the bulk, or -^V of the weight of the common air, the 

 effect on the lime-water was such as could not possibly have been overlooked in 

 my experiments. But as those who suppose fixed air to be generated by the mix- 

 ture of nitrous and common air, may object to this manner of trying the expe- 

 riment, and say, that the quantity of fixed air absorbed by the lime-water was 

 really more than T '- of the bulk of the common air, being equal to that quantity 

 over and above the air generated by the mixture, I made another experiment in 

 a different manner; namely, I filled a bottle with lime-water, previously mixed 

 with as much nitrous acid as is contained in an equal bulk of nitrous air, and 

 having inverted it into a vessel of the same, let up into it, in the same manner 

 as in the above-mentioned experiments, a mixture of common air with T '- of its 

 bulk of fixed air, till it was half full. The event was the same as before; 

 namely, the cloudiness produced in the lime-water was such that I could not pos- 

 sibly have overlooked. It must be observed, that in this experiment no fixed air 

 could be generated, and a still greater proportion of the lime-water was turned 

 into nitrous selenite than in the above-mentioned experiments; so that we may 

 safely conclude, that if any fixed air is generated by the mixture of common and 

 nitrous air, it must be less than -^ of the bulk of the common air. 



As for the nitrous selenite, it seems not to make the effect of the fixed air at 

 all less sensible, as I found by filling two bottles with common air mixed with 

 -j-i-5- of its bulk of fixed air, and pouring into each of them equal quantities of 

 diluted lime-water; one of these portions of lime-water being previously diluted 

 with an equal quantity of distilled water, and the other with the same quantity 

 of a diluted solution of nitrous selenite, containing about -^-j- of its weight of 

 calcareous earth ; when I could not perceive that the latter portion of lime-water 

 was rendered at all less cloudy than the former. Though the nitrous selenite 

 however does not make the effect of the fixed air less sensible, yet the dilution 

 of the lime-water, in consequence of some of the lime being absorbed by the 

 acid, does; but I believe not in any remarkable degree. 



There is an experiment, mentioned by Mr. Kirwan, which, though it cannot 

 be considered as an argument in favour of the generation of fixed air, as he only 

 supposes, without any proof, that fixed air is produced in it, does yet deserve to 

 be taken notice of as a curious experiment. It is, that, if nitrous and common 



