Mr. Cavenpisn’s Experiments on Air. 145 
ftandard of different parts of which varied from 3 to 46 5, but 
at a medium was 3,35. The matter remaining in the retort 
diffolved readily i in water, and tafted alcaline and cauftic. On 
adding diluted {pirit of nitre to the folution, {trong red fumes 
were produced; a fign that the acid in it was very much phlo- 
gifticated, as no fumes whatever would have been produced on 
adding the fame acid to a folution of common nitre; that part 
of the folution alfo which was fuperfaturated with acid became 
blue; a colour which the diluted nitrous acid is known to af=’ 
fame when much phlogifticated. The folution, when fatu- 
rated with this acid, loft its alcaline and cautftic tafte, but yet 
tafted very different from true nitre, feeming as if it had been 
mixed with fea-falt, and alfo required much lefs water to dif- 
folve it; but on expofing it for fome days to the air, and add- 
ing frefh acid as faft as by the flying off of the fumes the al- 
cali predominated, it became true nitre, unmixed, as far as I 
could perceive, with any other {alt *. 
It has been remarked, that the dephiogifticated air procured 
from nitre is lefs pure, than that from red precipitate and many 
other fubftances, which may perhaps proceed from unglazed 
earthen retorts having been commonly ufed for this purpofe, 
and which, conformably to Dr. PrrestLey’s difcovery, may pof- 
fibly abforb fome common air from without, and emit it along 
with the dephlogifticated air; but if it fhould be found that the 
dephlogifticated air procured from nitre in glafs or glazed ) 
earthen veffels is alfo impure, it would feem to fhew that part 
weight of the dephlogifticated air, fuppofing it 800 times lighter than water, is one 
tenth of that of the nitre, In all probability it would have yielded a much greater 
quantity of air, if a greater heat had been applied. 
* This phlogittication of the acid in nitre by heat has been obferved by Mr. 
SceweEe ; fee his experiments on air and fire, p. 45, Englifh tranflation. 
Vor. LXXIV, U of 
