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As I mean thefe letters to contain a general outline of 
what I have lately obferved with refpedt to air, I fliall 
add, that by the favour of that mob intelligent and ge- 
nerous chemift Mr. wolfe, I have lately procured fome 
of that phofphoric fpar, from which a new mineral acid, 
firft difcovered in Sweden, is procured. This acid, as 
well as the marine, vitriolic, and vegetable, I throw into 
the form of air, confined by quickfilver; and thus have 
an opportunity of examining its affinities with the great- 
efl eafe and certainty. I fliall in this place only obferve 
with refpe(St to it, that this acid air decompofes nitre, hut 
not near fo rapidly as the marine acid air; and that the 
fait which is formed by its union with alkaline air is not 
fenfibly foluble in ivater. I am, &c. 
P. S. Upon fecond thoughts, I am not fo well fatisfied 
with my conjecture, hinted in the letter to Dr. price, 
that fixed air may be a modification of the nitrous acid, 
though the experiment there mentioned feems to make 
it probable. But I lay no ftrefs upon any opinions, far- 
ther than as they may lead to the difcovery of new faCts^ 
XXXIX. An 
