Analyfis of the Air* 275 ? 
This continual fupply of frefh air to the 
fuel feems hence alfo very neceffary for 
keeping a Fire alive 5 becaufe it is found, that 
a Brimflone Match will not take Fire in 
a vacuum , but only boil and fmoke 5 nor will 
Nitre incorporated into Brown Taper then 
detonize, except here and there a Angle grain, 
that part only of the Taper turning black 
on which the focus of the burning glafs falls ; 
nor would they burn when a half exhaufted 
receiver with fumes in it was filled with 
frefh air added to thofe fumes : In which 
cafe it is plain, that a good quantity of the 
fuppofed vivifying fpirit of air nuift enter 
the receiver with the frefh air, and confe- 
quently thofe fubftances fhould take fire? 
and burn for a fhort time at leaft, which yet 
they did not. 
And that the air’s elafiicity conduces much 
to the intenfe burning of Fires, feems evident 
from hence; that Spirit of Nitre (which 
by Experiment 75 has but little elaftick air- 
in it) when poured upon live Coals, ex- 
tinguishes inftead of invigorating them : 
But Spirit of Nitre , when by being rnixt with 
Sal Tartar it is reduced to Nitre , will then 
flame, when thrown into the Fire, viz. be- 
caufe Sal Tartar abounds withclaftick aerea! 
T 4 par 
