816 ORGANIC 
long tube filled with chloride of calcium; and 
this drying apparatus is fitted by a sound cork 
to the retort he. This latter is laid in a shal- 
low trough open at one end, which is slightly 
elevated ; the trough is then filled with sand 
heated to about 212° F., and cautious exhaus- 
tion is performed by the syringe, taking care 
that none of the charge is carried out of the 
tube by the current of air; on gradually open- 
ing the stop-cock air is slowly re-admitted, 
being dried in its passage over the chloride of 
calcium ; it is allowed to remain in the appa- 
ratus a few seconds, and the exhaustion re- 
peated ; these operations are performed in suc- 
cession ten or twelve times. - is, acho 
rarely necessary to resort to this process o 
desicetion, and it is objectionable from the 
ease with which many compounds rich in hy- 
drogen decompose the oxide of copper at com- 
tively low temperatures. 
PaThe rying isha dave been accurately 
weighed is next fitted to the dried perforated 
cork, and connected by it air-tight to the retort 
tube; this is now placed in the furnace, which 
has been disposed’ in a convenient place rest- 
ing on bricks; to the drying tube the potash 
apparatus, also previously weighed, is attached 
by a connecting piece of caoutchouc, taking 
care that the largest bulb is on the arm con- 
nected with the drying tube; the ager ap- 
paratus should be slightly inclined by placing 
a cork under the end of the horizontal portion 
nearest the open extremity. Matters being 
thus arranged, we proceed to ascertain if the 
whole be tight, and for this purpose expand 
the air in the large bulb by heat, so as to ex- 
pel a few bubbles; if, on cooling, the liquid 
rise in the limb and maintain its elevation 
steadily for a few minutes, the combustion may 
safely be begun. Charcoal broken into pieces 
about the size of a walnut is ignited in a cru- 
cible furnace or by any other convenient 
means, and when red-hot applied to the por- 
tion of the tube nearest the cork where the 
te oxide of copper lies; the action of the 
feet is limited by a double sheet-iron screen 
which fits into the furnace, and has a central 
slit which allows it to bestride the tube; this 
screen can by degrees be moved further and 
further down the furnace until the whole tube 
is heated. An additional screen of single iron 
plate is hung over the closed end of the fur- 
nace to protect the cork, which usually should 
reach to within an inch of the fire, care being 
taken that the heat never rises so high as to 
scorch it, or falls so low as to allow of the 
condensation of moisture in the portion of the 
retort which projects from the furnace. 
' When the first part of the retort is red-hot 
and the escape of air from expansion has 
ceased, about an inch more of it may be 
heated, and so the fire gradually carried 
down; about three bubbles of air may pass in 
two seconds, it is better not to attempt a more 
rapid disengagement. At first but a small 
portion of erg gas is absorbed, but when the 
substance is fairly undergoing decomposition, 
and the atmospheric air in the apparatus has 
been expelled, it is almost entirely taken up by 
ANALYSIS. 4 | 
the potash-ley. When the whole tube is ig- — 
nited the heat must be continued till bubbles 
are no longer disengaged ; the potash-ley will — 
now gradually recede into the pe 
ad 
when this is observed to commence, the ¢ 
coal must be removed from the tail of the tubes 
and as soon as the potash has risen to fill half 
the large bulb, the tip of the tail must be 
i a off, and over the opened extremity; 
tube about eighteen inches long, and one quarter 
in diameter, should be supported; gen’ c 
tion is then effected by spi 7 tube (fig. 43 
D) fitted to the free extremity of the potas 
apparatus, drawing air through the combustio} 
tube to displace the carbonic acid and aqu 
vapour it contains. The use of the 
over the end of the retort is to supply pure ai 
and to prevent that from the furnace ch 
with carbonic acid from passing freely 
the apparatus: the actual process of com 
tion performed in the manner above deseril 
yanally poompias from an hour to an hour a 
a half. : 
The plan of drawing air through the tube 
that practised by Liebig, and it admits of cor 
siderable accuracy. Dumas, however, co 
nects the extremity of the retort with a dryit 
tube, and this again with a receiver containiz 
oxygen, which gas is carefully driven over 
contents of the tube. This renders the o 
ration somewhat more complicated, but if 
unquestionably more exact, pe pe in ¢ 
poende where the proportion of carbon is grez 
he tube for supplying oxygen is easily 
justed to the retort by drawing out the t 
horizontally instead of obliquely, fitti 
on by a caoutchouc connector, care being tal 
to screen the junction from the influence 
heat. i ' 
The apparatus is now dismounted, 
whole pia to cool; in about an h 
drying tube may be weighed, and the inere 
of weight carefully noted; one-ninth of 
gain indicates the quantity of hydrog 
substance contained ; the potash apparatus 
also weighed, and three-elevenths of wha 
has gained shews the quantity of carbon, — 
deficiency is oxygen. 
The oxide of copper used in the 
riments may again be rendered servic 
moistening it with nitric acid, and ignitii 
before. _ 
2. Analysis of a liquid not containing 
trogen. _Z 
f the fluid be volatile, we take a pie 
tube rather less than a quarter of an 
meter, heat it in the blowpipe flame, an 
on it a capillary portion about four i 
long; about a quarter of an inch below 
the tube is sealed ; the little piece of tub 
left connected with the capillary part h 
and blown into a small bulb tas b 
good-sized pea; this is cut off, i 
pillary neck of about two inches long. ; 
made a sufficient number of these Ob 
we take two of them, which we haye 
tained will freely enter the combusti 
and weigh them accurately ; a little of t 
to be analysed is put into a small tube, an 
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a 
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_as 
