5 SR) er 
eed 
* 
On the Preparation of Writing Ink. 137 
# the retort, (if one be employed,) or into a Wolf’s appa- - 
ratus, and pafling into the upper part of the fmall receiver, 
as exprefled in the plate at C. By employing mercury for 
fuch experiments, another advantage is gained by the ule of 
this apparatus, namely, a power of exhauition in the retort, 
or Woltf’s bottle, equal to a column of two inches of mer- 
_ curyy or 28 inches of water: This will be eafily conceived 
when it is recolleéted that, by drawing up the large receiver 
A, the fmall one C is raifed in its ciftern, bearing up with 
* it the contained mercury, which is kept in its place by the 
preffure of the atmofphere on the furface of the mercury in | 
the ciftern. The cock of the fimall receiver C is then to be 
turned off, and that of the large one A to be turned on. The 
_ air, of which the retort, or Wolf’s bottle, i is thus exhaufied, 
may then be let out, by plunging A into the mercury be- 
tween the cylinders BB, and turning off the cock. When 
_a fufficient quantity of gas pafles from the retort, or bottle, 
through the bent tube into C, to level the mercury in it and 
the ciftern, the communication may again be opened, and 
the fame fieps followed as before defcribed. By this means 
I have been enabled to obtain more gas, from the fame ma- 
terials, than if I had received it through a fluid of the weight 
of water; a circumftance of fome importance where nice dud 
accurate peli are looked for. 
The plate of the apparatus is on a {cale of nearly three 
inches to a foot. 
ee 
VUHI. A Communication refpediing the Preparation of Writing 
ee 
Ink. By Mr. DEsORMEAUX junior. 
Mr. Epiror, 
EING a conitant reader of your truly inftruétive and 
entertaining Work, and having noticed in the Number for 
Oétober, p. 29, a communication relative to an improved 
writing ink, Lam, in confequence, induced to offer fome prac- 
tical remarks on that fubject. 
Previous to my reading that communication refpeéting 
the difcoyeries of Prouft having been applied by Van Mons 
to 
