ATMOSPHERICAL AIR. <j 



fphere. For want of this the neareft approxhna.tion that 

 we can make appears to me to be by the ufe of nitrous air. 



Since when two meafures of pure nitrous air are mixed 

 with one meafure of pure dephlogifticated air, they both, 

 as nearly as poffible, dilappear, and form nitrous acid, 

 which is imbibed by the water in which the mixture is 

 made, it is evident tliat little or no phlogifticated air is 

 necefTarily formed in this procefs ; and when it is con- 

 ducted properly, there will appear to be a much gteater 

 proportion of dephlogifticated air in the atmofphere than 

 has been fuppofed, and enough to be converted into 

 phlogifticated air in the procefs above mentioned. But 

 a confiderable time is neceftiiry for this purpofe ; becaufe 

 the diminution continues much longer than has been 

 hitherto imagined. 



The difference between the degree of diminution of at- 

 mofpherical air by a mixture of nitrous air, with, or 

 without, agitation, is very confiderable. In general, 

 without agitation, equal meafures of each will occupy 

 the fpace of 1.25 meafures, but with agitation only i.oi ; 

 and if the computation be made from this laft datum, it 

 will give the proportion of dephlogifticated air to be 27 

 parts in 100, and confequently that of the phlogifticated 

 air 73. But by keeping the mixture a longer time, the 

 diminution will proceed to about 0.6 of a meafure which 

 will give 46.6 for the proportion of dephlogifticated air, 

 and 53.4 for that of the phlogifticated air in the at- 

 mofphere. 



This diminution in the mixture of nitrous and atmo- 

 fpherical air, which is effeded in the courfe of time, is 

 various, depending, no doubt, on feveral circumftances 

 which I have not yet been able to afcertain. What I have 

 adlually obfervcd is as follows. 



On the 2ift of July 1 mixed equal quantities of nitrous 

 and atmofpherical air; when, with agitation, they oc- 



B cupied 



