794 ORGANIC 
which combines the application of moderate 
heat with Leslie's Seethind: already described, 
may be advantageously employed, though the 
manipulation is rather complicated and trouble- 
some. In a counterpoised retort which will 
sustain exhaustion, a given weight of the sub- 
stance to be dried is placed and connected with 
a tubulated receiver containing oil of vitriol, by 
a sound cork secured on the exterior with several 
folds of bladder, well soaked before applying it. 
Through the tubulure of the receiver passes a 
small glass tube. This junction likewise is ren- 
dered air-tight, with a cork and bladder. The 
tube, about an inch from the tubulure, is, previous 
to its insertion, drawn out and narrowed toa 
capillary bore, so that at pleasure it may be easily 
drawn off and sealed by a jet of flame from the 
blowpipe. Matters being thus arranged, the 
tube from the receiver is united by a connecter 
of caoutchouc with another tube, and this again 
with the air-pump, and exhaustion is performed. 
When a sufficient vacuum has been produced, 
the whole is allowed to stand for an hour. If, 
at the end of that time, the mercury in the 
gauge retain its level, the apparatus is air-tight 
and may be detached from the pump by seal- 
ing the tube proceeding from the receiver in 
its capillary portion. We may now apply a 
gentle heat to the bulb of the retort by means 
of a water bath, or otherwise, and can cool the 
receiver. Great caution is of course requisite 
in handling the exhausted vessels, as the 
slightest abrasion of the surface might cause 
fracture. 
In some cases, as in drying blood, a tempe- 
rature of 230° may be safely used by employing 
a boiling solution of Rochelle salt as the exte- 
rior bath; and in the analysis of the bile a heat 
of even 260° is recommended by Berzelius. 
Where sugar or urea is present, even a heat of 
200° is injurious, and must therefore be avoided, 
The operation we are now considering appears 
one of the simplest that the chemist can have 
to perform, but I have been induced to dwell 
the longer upon it as it is one from which, 
without great care, more mistakes arise than 
from any other, owing to the pertinacity with, 
which water adheres to most organic substances. 
The temperature attainable in an open basin 
over the water bath is much lower than we 
should, @ priori, have been led to imagine. 
I found, for example, that the temperature of 
some wheat flour thus drying in an open basin 
was only 144° F., whilst the water in the bath 
continued steadily at 196° F. When the basin 
was covered with a piece of paper, a tempe- 
rature of 161° F. was the highest attained, 
while a thermometer placed in the water of 
the bath stood at 194° F. With liquids eva- 
porating it rises somewhat higher ; when plain 
water was evaporated it stood at 164°, the water 
in the bath being 208°; and in the case of a 
viscid fluid like yeast, it varied between 176° 
and 180°, while the bath raised a thermometer 
inserted in it to 210°. 
It is therefore desirable to have an appa- 
ratus in which we can ensure any given tempe- 
rature from 212° upwards. For this purpose 
Liebig has contrived a kind of hot-water oven, 
i, 
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ANALYSIS. ¥} 
consisting of a double box of copper; in the 
interval between the outer and inner walls, 
water, saline solutions, or oil, may be poured 
and heated in the usual way. In one side of 
this box is a door which may be closed whe 
necessary. The interior chamber and its con. 
tents can thus be maintained with certainty 
the same temperature as that of the fluid around 
them. The best plan of proceeding consists 
evaporating liquids to apparent dryness up 
the open water bath ; and parnaatld subjectin 
the solid residue, when a temperature of 
is not injurious, to complete desiccation — 
Liebig’s oven. So long as the material un¢ 
examination loses weight, the application 
heat must be continued. 
Capsules of Wedgewood ware or B 
porcelain are indispensable, and one or | 
small platinum dishes will be found most val 
able, especially in the evaporation of al 
minous fluids, as the dry residue adheres 
strongly to the glaze of earthen vessels that 
portion of the basin is invariably remov 
along with the animal matter, which 
quires an undue increase of weight, and 
surface of the vessel becomes rough and ut 
for use from the difficulty of cleaning it. — 
Berlin porcelain crucibles are excellent ve 
for evaporation, as, being fitted with covers, 
dry residue may be preserved from absorl 
moisture during the operation of weighing 
exposure to air. It may be worthy o 
tice that adhering organic substances ma 
removed from the surface of vessels in wh 
they have been kept, by digestion in cot 
trated nitric or sulphuric acid, or else by si 
solution of potash. ' 
Incineration of the dry residue is ac 
plished by taking a counterpoised porcela 
platinum capsule with a determinate quanti 
say 10 or 12 grains, of the material to be bu 
and heating it over a circular wicked spirit 
until the ash completely loses its black ¢ 
The capsule should at first be covered t 
vent loss by dispersion on the first appli 
of heat; when visible fumes cease to ar 
cover may be removed to allow freer a 
air; as, however, the temperature 
when the vessel is covered, it will o 
found advantageous to leave it loosely ¢ 
and maintain a steady heat; sufficient a 
access to consume the carbonaceous — 
Sometimes the ash may be stirred ¢: 
a platinum wire in order to expose it moi 
to the air. When the ash contains | 
phosphates, the last traces of carbon are 
off with difficulty, as the phosphates fu 
protect the unburned particles from th 
action of the air. This inconvenience 
overcome by moistening the residue ( 
capsule has been allowed to cool) wil 
drops of nitric acid, and again ignitin: 
ing this maneeuvre as often as mayb 
sary. A new difficulty, however, aris 
chlorides are present, as is almostalw 
case; for ata high temperature th 
decomposed by nitric acid, and t 
therefore appears to contain less chlort 
is really combined withit. ~~ ~ 
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