A Manual of the Chemistry of the Carbon Compounds

in THE CHEMISTRY OF
a mixture of nitre nnd sodium carbonate. The metallic compounds
thus formed are converted according to well-known methods of
quantitative analysis into compounds fit for weighing.
Oxygen, cannot be determined directly, but its quantity is always
found by difference; by subtracting all the constituents which have
been directly estimated from the total weight of the substance taken,
the difference gives the weight of the oxygen.
CatmMiori, of (he Analysts*—In order to compare the results of
different analyses the percentage composition is first calculated
as follows:—
(1) 0*1460 grams of hexane yielded, by combustion with copper
oxide, 0-4490 of carbon dioxide and 0-2135 water.
Now, as 44 parts by weight of carbon dioxide contain 12 parts of
carbon, we find the weight of carbon by multiplying by £f or -^r, and
the weight of the hydrogen is obtained by dividing the weight of the
water by 9. The following equations therefore give the percentage of
carbon and hydrogen in hexane:—
0449x3x100
0146 x 11
0*2135 x 100 1r_
0140 x 9 "
= 1 C a
100 parts of hexane consist therefore of—
Carbon 838
Hydrogen 163
1001
(2) 0395 grams of acetic acid gave 0580 of carbon dioxide and
0*235 of water, 100 parts contain therefore-"
Carbon 400
Hydrogen , G'o
As these numbers do not add up to 100, the difference must be
caused by the presence of oxygen, for qualitative analysis has shown
that acetic aoid does not contain any other elements but these three.
Its percentage composition is therefore—
Carbon 40-0
Hydrogen 6*6'
Oxygen 534
1000
(3) The analysis of caffeine, au organic base contained in coffee
and tea, gave the following results:—
0*3827 of substance gave on combustion with copper oxide in presence
of metallic copper 0*6948 of carbon dioxide and 0*1800 of water.
0*1350 of substance was heated with soda lime, and the ammonia
(or compound ammonia) evolved was absorbed by hydrochloric acid.