154 Defeription of a Mercurial Gaxometer. 
containing this principle only, is capable of yielding that 
moft noxious compound. When feptic acid thus exifts in 
the alimentary canal, and carbonates, tartrites, &c. of pot- 
ath, are taken down, the ftronger acid is attraéted, and a 
proportional quantity of nitre or faltpetre is formed. Thus, 
in abundance of cafes, the praétifers who are fond of pre- 
feribing feptite of pot-afh might fpare themfelves the trouble, 
as. that faline compound is, in certain cafes, formed in the 
ftomach and bowels in confiderable quantity. What precife 
effect the nitre fo formed has on the inteftines, and on the 
conftitution at large, deferves to be inquired into with great 
care; for | am not without apprehenfion that fome of the 
fad fymptoms, occafionally attendant on fevers, are modified ~— 
by the feptite of pot-ath formed within the belly.—I believe, 
however, I muft now ftop, and trouble you no further for 
the prefent than by affuring you, that I hope much from 
-your aid in this inquiry, which you inform me you confider 
f€ as a happy train of difcovery ; 3” and that I am, very re- 
fpectfully, yours, 
SAM. L. MITCHILL, 
To Dr, Priefiley. 
VIL. Defcription of a Mercurial Gazometer conftrudted by 
Mr. W.H. Pepys jun. Communicated by the Author. 
if ME difficulty attending the exhibition of acid and al- 
kaline gafes, was the firft idlgeainent to. Prieftley, Lavoifier, 
and memees, to ufe mercury for fuch experiments; but the 
great expence and enormous weight of this fluid obliged 3 
many accurate and experienced chemifts to relinquifh them 
almoft entirely, as there appeared no other likely means of t 
fucceeding but by its means and that of the exhaufted re- 
ceiver. A contrivance to leffen the quantity of mercury 
neceffary for fuch experiments was therefore a defirable ob- 
jet; and by introducing the dome ufed by Mr. Watt in his — 
“hydraulic bellows, I have fucceeded in conftruéting an ap+ — 
paratus in which both of the above-mentioned requifites are 
obtained at a comparatively {mall expence. As it is hardly 
| | poflible 
