Formation of nitrous Acid. 267 
different, the former parcel being all ufed- It was prepared, 
like the former, from turbith mineral, but was rather purer, 
as it feemed to contain only f- of phlogifticated air. The 
proportion in which it was mixed with common air was that of 
22 to 10; lo that a greater proportion of common air was 
now ufed, in confequence of which it was not neceffiiry for 
Mr. Gilpin to introduce common air fo often. 
On February 29, the refervoir was again filled with air of 
the fame kind, in prefence of fome of the fame Gentlemen. 
As it was found by the laft experiment that we muft not de- 
pend on the figuration of the foap-lees being made known by 
any alteration in the rate of diminution, the procel's was 
flopped as fioon as the air abforbed was fuch as from my own 
experiments i judged fufficient to neutralize the foap-lees- 
This was effedted on the 15th of March. The air remaining 
in the tube, when Mr. Gilpin left off working, was 600 
meafures ; but at the time the produce was examined, it was 
reduced to about 120, lo much having been abforbed without 
the help of any electrification, which is a {till more remarka- 
ble inftance of fpontaneous abforption than what occurred in 
the former experiment. A few days after the experiment be- 
gan, a black film was formed in one of the legs, which, I 
fuppofe, muft have been a mercurial etbiops ; but whether 
owing to fome fmall degree of foulnefis in the mercury or tube, 
or to any other caufe, I cannot tell. This foulnefs feemed not 
to increafe ; but on March 10, when the air abforbed was 
about 5200, a whitifh fediment began to appear on the furface 
of the mercury. 
On March 19, the produce was examined in the prefence of 
Dr. Blagden, Dr. Dollfuss, Dr. Fordyce, Dr. Heber- 
den, Dr. J. Hunter, Mr. Macie, and Dr. Watson. 
Vol. LXXVIII. O o The 
