r^c Mr. cavendish’s Account of 
ferent times and places, by affuming common air and perfe&ly 
phlogifticated air as fixed points. Thus, it the teft of any air 
is found to be the fame as that of a mixture of equal parts ot 
common and phlogifticated air, I would fay, that it was half 
as good as common air ; or, for fhortnels, I would fay, that its 
frandard was \ : and, in general, if its teft was the fame as that 
of a mixture of one part of common air and x of phlogifticated 
air, I would fay, that its ftandard was 
i 
In like manner, if 
one part of this air would bear being mixed with vV of phlo- 
gifticated air, in order to make its teft the fame as that of 
common air, I would fay, that it was i -\-x times as good as 
common air, or that its ftandard was i+.v; confequently, if 
common air, as Mr. scheele and la voisier fuppofe, con- 
lifts of a mixture of dephlogilticated and phlogifticated air, the 
frandard of any air is in proportion to the quantity of pure de- 
phlogifticated air in it. In order to find what teft on the 
Eudiometer anfwers to different ftandards below that of com- 
mon air, all which is wanted is to mix common and perfectly 
phlogifticated air in different proportions, and to take the teft of 
thofe mixtures ; but in ftandards above that of common air, it 
is neceflary to procure fome good dephlogilticated air, and to 
find its ftandard by trying what proportion of phlogifticated 
air it muft be mixed with, in order to have the fame teft as 
common air, and then to mix this dephlogilticated air with 
different proportions of phlogifticated air, and find the teft of 
thofe mixtures 
Oil 
* The rule for computing the ftandard of any mixture of dephlogilticated and 
phlogifticated air is as follows. Suppofe that the teft; of a mixture of D parts of 
dephlogilticated air with P of phlogifticated air is the fame as that of common. 
