Sequel to Mr. Watt's Thoughts, &c 2e% 
¢an be made appear in any of the known forms of that acid 
and unlefs retorts can be obtained of a true apyrous and com- 
pact porcelain, I fhould prefer glafs retorts, properly coated, 
for making experiments for the prefent purpofe. 
In fome of my experiments the nitre was left in the retort 
placed in a furnace, fo that it took an hour or more to cool: 
In thefe cafes there was always a deficience of the acid part; 
which feemed, from fome appeafances on the coating, either 
to have penetrated the hot and foft glafs, by pafling from par- 
ticle to particle, or to have efcaped by {mall cracks which hap- 
pened in the retort during the cooling. ‘There was the leaft 
deficience of the acid when the diftillation was performed as 
quickly as was practicable, and the retort was removed from 
the fire immediately after the operation was finifhed. In order 
to fhorten the duration of the experiment, and confequently to 
lefflen the action of the nitre on the retort, it is advifable not 
to diftil above 56 ounce meafures of dephlogifticated air from 
an ounce of nitre. The experiment has fucceeded beft when 
the retort was placed in a charcoal fire in a chafing-dith or 
open furnace; becaufe it is eafy in that cafe to ftop the opera- 
tion, and to withdraw the retort at the proper period. 
When the dephlogifticated air is diftilled from the nitre of 
mercury, the folution fhould be performed in the retort itfelf, 
and the nitrous air produced by the folution fhould be caught 
in a proper receiver, and decormpofed by the gradual admiffion 
of common ait through water; and the water, which thus be- 
comes impregnated with the acid of the nitrous air, fhould be 
added after the procefs to the water through which the dephlo- 
gifticated air has pafled. When the folution ceafes to give any 
more nitrous air, the point of the tube of the retort fhould be 
raifed out of the water; otherwife, by the condenfation of the 
Aaa2 watery 
