f 160 j 
dephlogifticated air if it bé ver¥ 
pure. 
What has been.already faid of 
this method of putting difftrent airs 
to the nitrous teft will be fufficients 
I hope, to guide the reader in imi+ . 
tating it. But he will find in the 
refult of every trial, made with the 
fame fpecies of ait, fo much differ+ 
ence, that he would | miftratt the 
‘whole method if he did not obterve 
every minute circum{tance in the 
courfe of the whole experiment. 
It has coft the Abbé fome years affi- 
duous labour before he reduced this 
‘method to that degree of accuracy 
which it has now acquired in his 
Thofe. who wifh to perform this 
amufing experiment. themfelves — 
will think it worth their while to 
= = : = look over the following neceflary 
cautions % 
