Page 5 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL II

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2 FIXED OILS, FATS, AND WAXES.

• The sp. gr. is less than that of water, ranging between the limits
of o.875 and o.97o; but if certain anomalous oils from marine animals
be excluded, the lowest density is about o.912 at a temperature of 15°C.
In the fluid state, at the temperature of boiling water, the sp. grs.
range from o.85o to about 0.910, The waxes and allied substances
are still lighter in the melted condition their sp. gr. ranging from o.808
to 0.845.
6. The fusing or melting points range within wide limits, and are
liable to modification in an obscure manner by special treatment.
7. They are practically insoluble in water, but dissolve to some
extent in absolute alcohol or strong spirit, especially when hot, and are
readily soluble in ether, chloroform, carbon tetrachloride, carbon
disulphide, benzene, petroleum spirit, turpentine, and other volatile
solvents. They are readily miscible with one another.
8. The fixed oils and fats are composed of carbon, hydrogen, and
oxygen, the nitrogen, sulphur, phosphorus, and iron present in many of
them being due to foreign matters, which often cannot be completely
removed.
9. They do not emit inflammable vapours at the ordinary tempera-
ture, but may be burnt by means of a wick. They are not capable of
being distilled at the ordinary atmospheric pressure without decom-
position. When heated alone they darken and evolve acrid offensive
vapours; and when further heated to about 315° carbon dioxide is
evolved, together with the peculiarly irritating vapours of acrolein,
C,H,O, various volatile organic acids, and gaseous, liquid, and solid
hydrocarbons. The temperature at which this decomposition occurs
has been improperly called the "boiling point" of the oil, the
phenomenon of apparent ebullition being really due to the escape of the
gases formed by the decomposition.
10. On distillation with superheated steam, they undergo a simpler
decomposition, with formation of glycerol and fatty acids. This
change may also be effected by acting on them with sulphuric acid
or a strong base. The action is known as "saponification," or
hydrolysis and its analytical application is discussed in another
section.
1. If air is excluded, the fixed oils may be preserved unchanged
for a lengthened period, but, on exposure to air, many of them thicken
owing to absorption of oxygen, and are ultimately converted (if ex-
posed in sufficiently thin layers) into a yellowish transparent skin or