ORGANIC ANALYSIS. 
best made by passing a piece of glass tube 
throngh a cork fitting accurately into the mouth 
of the combustion tube and connecting the 
brass apparatus to this small glass tube by a 
caoutchouc connector; the limb (b) is fastened 
by a similar joint to a glass tube (e) bent at 
right angles near one end, with a straight por- 
tion upwards of thirty inches long, the other 
extremity of which is turned up at an acute an- 
gle for the convenience of safely delivering the 
gas; the tube is placed in a vertical direction 
with its lower upturned extremity dipping into a 
small mercurial trough ; the stop-cock tube (c) 
is connected with an exhausting syringe and 
a vacuum produced ; the apparatus is left for 
half an hour to ascertain that all the joints are 
tight: if the mercury after this lapse of time 
still stands at the same level, the experiment is 
proceeded with ; a moderate heat is applied by 
a spirit lamp to the end of the retort contain- 
ing the carbonate ; by this means carbonic acid 
is set free and displaces the last portions of air; 
the exhaustion and disengagement of gas are 
repeated alternately three or four times, taking 
care to leave sufticient carbonate undecom- 
posed to renew this expulsive process at the 
termination of the experiment. The stop-cock 
{c) is now closed, the air-pump is removed, 
and a graduated jar containing some solution 
of potash is inverted in the mercury over the 
recurved -extremity of the long glass tube. 
The copper turnings are then brought to red- 
_ hess in the usual way by charcoal, and the 
_ €xperiment conducted with the customary pre- 
cautions, the decomposition being caused to 
_ take place less rapidly than usual; when the 
_ part of the retort containing the matter for 
_ analysis is red-hot through its entire extent, 
heat is gradually applied to the carbonate at 
the end, and the last portions of gas from the 
_ combustion in the apparatus are driven into 
_ the receiver by the disengaged carbonic acid. 
As the products of combustion are only 
_ water, carbonic acid, and nitrogen, the two 
_ former are retained by the solution of potash, 
_ whilst the latter alone presents itself for mea- 
_ surement. I need hardly say that the height 
of the barometer and thermometer must be 
_ carefully noticed, when the apparatus by stand- 
ing for an hour or two has reached the tem- 
_ perature of the atmosphere ; as the gas will be 
Saturated with moisture, its volume must be 
_ corrected by the known methods for the three 
_ points of temperature, pressure, and moisture ; 
then, since 100 cubic inches of nitrogen at 
Standard temperature and pressure weigh 
30.15 grs., the weight of the nitrogen that a 
given quantity of the matter analysed contains 
is easily determined. In this process, as in 
every case where the proportion of nitrogen 
alone forms the object of our experiment, after 
the weight of the material for analysis has been 
once accurately determined, it is evident there is 
nothing to fear from the absorption of moisture. 
Occasionally the quantity of nitrogen, where 
large, is advantageously determined by making 
the combustion just as though we were going 
to ascertain the proportion of carbon and hy- 
drogen; but, instead of condensing the car- 
819 
bonic acid and weighing it, the whole of the 
gases produced are collected over mercury. 
A bent gas-delivering tube is substituted for 
the usual are ee ( Fig. 431.) In 
this case it is best to begin at the closed ex- 
tremity of the tube, and having expelled the 
atmospheric air by a portion of gas generated 
from the substance, to collect the rest of the 
gaseous products in a graduated jar; by agi- 
tating the gas with solution of potash the pro- 
portion of nitrogen to carbon is at once deter- 
mined, as equal volumes of carbonic acid and 
nitrogen represent single equivalents of carbon 
and nitrogen. It is not necessary in this case 
to determine accurately the quantity of mate- 
rial acted upon. 
Experience has shewn that in the preceding 
process for organic analysis the quantity of 
hydrogen deducéd from it ‘is always slightly in 
excess, usually about 0.2 parts in 100, whilst, 
unless chromate of lead or chlorate of potash 
is employed, the carbon is sometimes as much 
deficient. A deficiency of carbon also occurs 
if the ash contain carbonates in any form. Oc- 
casionally sulphur and chlorine are among the 
constituents of organic bodies ; the methods of 
analysis must then be modified. For details 
upon these subjects the reader is referred to the 
treatise of Berzelius. ’ 
We will suppose the labour of analysis thus 
brought to a successful issue. It is, however, 
evident that the information derived from this 
source alone is but scanty, as we can thereby 
form no idea either of the number of equiva- 
lents of each element entering into the com- 
position of an organic body, or of its relations 
to the substances concerned in its production 
or obtainable from it by its decomposition. 
Whenever it is possible,the equivalent or com- 
bining proportion of the compound must be 
determined. This is effected by preparing a 
compound of the body with some substance, 
whose equivalent is well known, and proceed- 
ing to analyse the new product. If our or- 
ganic substance be soluble in water, and 
capable of entering into combination with 
oxide of silver, this oxide is for many reasons 
preferred. Oxide of silver combines with very 
many organic bodies, and forms with them 
compounds insoluble or sparingly soluble in 
water. They may generally be formed by 
double decomposition, and washed from all 
adhering impurities ; fifteen or twenty grains of 
the silver compound is accurately weighed in 
a counterpoised porcelain crucible. It is then 
carefully incinerated till pure silver alone re- 
mains. On again weighing, the loss will give 
that of the body combined with the silver, and 
in addition that of one equivalent of oxygen 
expelled from the oxide of that metal at a red 
heat. The residual silver should dissolve 
without remainder in nitric acid. Now, 
since the equivalent number of silver on the 
hydrogen scale is 108, it is evident that by 
simple calculation we may determine the equi- 
valent, number of the organic body that had 
combined with it. 
An example will perhaps elucidate my mean- 
ing more distinctly. 
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