Page 9 - A TEXTBOOK OF ORGANIC CHEMISTRY

CALCULATION OF EMPIRICAL FORMULA 3

Constituents of the Carbon Compounds

Many organic substances are composed of carbon and hydro-
gen only, and are then termed hydrocarbons, for instance,
ethylene, benzene, petroleum, naphthalene, and oil of turpen-
tine; a vast number consist of carbon, hydrogen, and oxygen,
for instance, wood spirit, alcohol, glycerine, aldehyde, oil of
bitter almonds, formic acid, acetic acid, steario acid, tartaric
acid, benzoic acid, carbolic acid, tannic acid, and alizarin;
many compounds contain carbon, hydrogen, and nitrogen,
for instance, prussic acid, aniline, and coniine; as examples
of compounds containing carbon, hydrogen, nitrogen, and
oxygen, may be taken urea, uric acid, indigo, morphine, and
quinine. In addition to these, sulphur, chlorine, bromine,
iodine, phosphorus, and, generally speaking, the larger number
of the more important elements, are also frequent constituents
of the carbon compounds.

Analysis of Organic Compounds
The methods adopted for the detection and estimation of
0, H, N, S, halogens, &e,, will be found in any book on Practical
Organic Chemistry. Within recent years micro-analytical
methods have become common as they require only a few
mgs. of material (ef. S. and J., Chap. IV and V).

The Calculation of the Empirical Formula
The same principle applies as in the case of inorganic com-
pounds, i.e. the percentage numbers found are divided by
the atomic weights of the respective elements, the relative pro-
portions of the quotients obtained being expressed in whole
numbers. For instance, acetic acid being found to contain
40-11 p.c. carbon, 6·80 p.c. hydrogen, and, consequently, 53-09
pc. oxygen, the quotients are to each other as 3-34 : 6·80: 3-32
1:2:l. The simplest analysis-formula of acetic acid would
therefore be CH,O. Sometimes figures are obtained which
correspond with equal nearness to different formulae, between
which it is therefore impossible, without further data, to choose.
For instance, a sample of naphthalene yields on analysis
93-70 p.c. carbon and 6-30 p.c. hydrogen; the quotient