C 179 ] 



fifty fubdivifions, which, being add- 

 ed to the above-mentioned 256, 

 will make their number in all 306 

 fubdivifions ; the difference of time 

 between the moment of the mix-* 

 ture of both airs and the examina- 

 tion will make alfo a confiderable 

 difference ; even a few feconds may 

 make a lenfible. difference, if the 

 examination be intended to be 

 finifhed in a little while ; but if the 

 two airs after their mixture are left 

 to ftand by themfelves a long while, 

 as for inftance 24 hours, the whole 

 refult will be uncertain, particularly 

 if the degree of goodnefs of dephlo- 

 gifticated air is to be examined. 



The remaining fource of error 

 confifts in letting up at once all the 

 quantity of nitrous air to be em- 

 ployed in the experiment. The un- 

 certainty of the refult arillng from 

 N 2 this 



