I t 
Formation of nitrons Acid . 275 
u verfion of air into nitrous acid by the ele&ric fpark. It is 
“ very difficult to guefs why an experiment does not fucceed, 
“ unlefs one is prefent and fees it tried ; but if you intend to 
u repeat the experiment, your bell way will be to try it with 
“ the fame kind of apparatus that J defcribed in that Paper. 
“ If you do fo, and obferve the precautions there mentioned, I 
u flatter myfelf you will find it fucceed. The apparatus you 
“ ufed feems objectionable, on account of the danger of the 
“ iron being corroded by abforbing the dephlogifticated air.” 
“ As to the dephlogifticated air procured from the black 
“ powder formed by agitating mercury mixed with lead, as 
“ it was foreign to the fubjedt of the Paper, and as I propofed 
“ to fpeak of it in another place, I did not defcribe my me- 
“ thod of procuring it. As far as I can perceive, the fuccefs 
“ depends intirely on carefully avoiding every thing by which 
Ci the powder can abforb fixed air, or become mixed with par- 
“ tides of an animal or vegetable nature, or any other inflam- 
“ mable matter : for which reafon care fhould be taken not to 
“ change the air in the bottle in which the mercury is fhaken, 
“ by breathing into it, as Dr. Priestley did, or even by 
“ blowing into it with a bellows, as thereby fome of the dull: 
<c from the bellows may be blown into it. The method which 
“ I ufed to change the air was, to fuck it out by means of an 
“ air-pump, through a tube which entered into the bottle, 
64 and did not fill up the mouth fo clofe but what air could 
“ enter in from without, to fupply the place of that drawn 
“ out through the tube. 
“ I am, &c.” 
With regard to the main experiment, it was not in my power 
to give him further information than I did ; as I pointed out 
Vol. LXXV 1 II. V p the 
