ORGANIC ANALYSIS. 
capillary neck of the bulbs inverted into the 
liquid; the bulbs are then warmed by the flame 
of a spirit-lamp, so that on cooling they shall 
be about three-fourths filled with the liquid. 
The necks are now sealed by the blowpipe- 
flame, and the bulbs again weighed ; the in- 
-_ erease of weight gives the quantity of the 
_ liquid which has entered, and which is to be 
_ analysed. The oxide of copper having been 
heated, and allowed to cool with the usual pre- 
cautions, about an inch and a half of the retort 
is filled with pure oxide; we then take one of 
the bulbs, draw a file across the capillary neck, 
put the bulb into the tube, break off the neck 
by pressure against the glass, and drop the 
broken portion in with the bulb; we then pour 
in a couple of inches of oxide of copper, 
introduce the second bulb in the same manner 
as the first, and fill up the tube with oxide, 
cork it and strike it smartly on the table as 
before to secure free air-way. The combustion- 
tube is now connected with the exhausting 
__ syringe, but no heat applied; on gently working 
_ the syringe, the air and vapour in the bulbs 
_ will expand and drive out the liquid, which 
_ will be quickly absorbed by the oxide of 
| copper around ; we adjust the apparatus in the 
_ furnace as before, and gradually heat the upper 
half of the tube; when this is red, we vola- 
_ tilize the fluid by cautiously approximating a 
piece of ignited charcoal, taking especial care 
not to heat the tube too much ; by degrees all 
the liquid in the first bulb is expelled, and we 
in like manner with the other; the 
_ whole tube is finally heated carefully, and the 
_ after part of the process conducted in the 
manner already described. 
If the liquid be not volatile, an oily acid 
for example, a small vessel is made by taking a 
_ piece of glass tube about a quarter of an inch in 
diameter, sealing one end, and while hot press- 
_ ing it on a flat surface, so as to make a firm 
_ basis on which it may stand upright; it should 
be cut off the tube so that the little vessel be 
about an inch high. It is weighed at first 
mpty, and a second time with the liquid for 
analysis; an inch or two of oxide of copper is 
put into the combustion-tube, then the vessel 
with the liquid. On inclining the tube suffi- 
ciently, the liquid runs out and is made to 
diffuse itself over the inner surface of the lower 
half of the tube, which is to be filled with oxide 
of copper, and the analysis to be cautiously 
] ed with in the usual way. 
_ Substances which contain a great excess of 
carbon sometimes escape complete combustion 
by this process; when this is feared, all danger 
may be averted either by adopting the plan of 
umas, already mentioned, or by pulverizing 
me chlorate of potash finely, which is care- 
fully dried, mixed with about four times its 
< of oxide of copper, and the first portion 
of the retort is filled with it for about an inch ; 
| the tail-like prolongation may in this case be 
| dispensed with at the close of the operation ; 
| instead of sucking air through the apparatus, 
we very cautiously apply heat to the chlorate, 
| oxygen is evolved, which burns the last traces of 
_ | carbonand displaces the gas and aqueous vapour 
VOL. III. 
817 
which the tubes contain. When the chlorate 
has been used, the last inch of oxide of copper 
must be kept separate from the rest, as it will 
be mingled with chloride of potassium, and 
must not be employed again until it has been 
washed from the salt, for as chloride of copper 
is slightly volatile it would be deposited in the 
drying tube and unduly increase its weight. 
If the heat is too suddenly applied, a portion 
of the chlorate is apt to be carried forward me- 
chanically, and this constitutes the chief ob- 
jection to its use. 
Sometimes chromate of lead is advantage- 
ously substituted for oxide of copper with sub- 
stances difficult of combustion, as by a bright 
red heat alone it gives off a portion of its oxy- 
gen. It is easily prepared by precipitating the 
chromate or bichromate of potash with solution 
of acetate of lead. It should be well washed 
and heated to incipient fusion before it is used 
for analysis. It has the advantage of being 
much less hygroscopic than the oxide of cop- 
per. To ensure accuracy, when much gas (as 
in this case, and in instances where nitrogen is 
present,) passes through the potash apparatus 
during the whole experiment, it is best to con- 
nect the open extremity with an additional 
drying tube, charged with solid hydrate of 
potash instead of chloride of calcium, the 
weight of which has been carefully noted, as 
a portion, very small but still susceptible, of 
aqueous vapour is carried off from the solution 
of potash by the gas, and would otherwise be 
lost, making the quantity of carbon appear 
somewhat too little. 
3. Analysis of a body containing nitrogen, 
Two separate analyses are in this case re- 
quired ; the first, to discover the proportion of 
carbon and hydrogen; and the second expressly 
for the nitrogen. When bodies containing 
nitrogen are burned with oxide of copper, a 
variable proportion of the lower oxides of 
nitrogen is formed, which being retained by 
the chloride of calcium or potash would render 
the analyses incorrect. A precaution is there- 
fore employed which renders it necessary to 
make use of a retort-tube somewhat longer 
than common; it is charged as usual to within 
four inches of the opening, and then filled up 
with clean copper turnings; the apparatus is 
arranged as before directed, the copper turnings 
are brought to full redness, and the analysis 
proceeded with cautiously in the ordinary man- 
ner. As the oxides of nitrogen pass slowly over 
the ignited copper they are decomposed, the 
oxygen combining with the copper while pure 
nitrogen escapes; the quantity of carbon and 
hydrogen is determined exactly as heretofore. 
To ascertain the proportion of nitrogen, the 
most accurate method is that recently devised 
by Varrentrapp and Will, and suggested about 
the same time by Berzelius; the fundamental 
fact consists in the observation of Gay Lussac, 
that when azotised matters are heated with a 
large excess of hydrate of potash (soda answers 
equally well), the whole of the nitrogen is ex- 
pelled in the form of ammonia. In order to 
render it available for the purposes of analysis 
the subjoined precautions are requisite. 
3G 
