g. 1.70). The temperature should not be allowed to rise above
40°. Allow to stand, and run off the "acid tar."
The oil is now shaken up with from 10 c.c. to 20 c.c. of sodic hydrate
solution (sp. g. 1.3), allowed to stand, warmed for half-an-hour, and
the "soda-tar" run off.
On mixing this soda-tar with dilute acid, the "crude shale oil creosote"
separates, and is measured off.
The purified oil is next re-distilled in fractions, which come over in
the following order:--"Naphtha," "light oil," "heavy oil," and "still
bottoms." For the first product, which is only got from certain shales,
the receiver is changed when the distillate has a specific gravity of
0.78. For the second product the process is continued till a drop of the
distillate, caught as it falls from the neck of the retort on a cold
spatula, shows signs of solidifying. This is "crude light oil."
The receiver is changed, and the "heavy oil" comes over; towards the end
a thick brown or yellow viscid product is got. The receiver is again
changed, and the distillation carried to dryness.
The "crude light oil" is washed cold with 2 per cent. of sulphuric acid
(concentrated), and afterwards with excess of soda. Thus purified it is
again distilled to dryness, three fractions being collected as before.
Naphtha, which is added to the main portion, and measured; "light oil,"
which is also measured; and "heavy oil," which is added to that got in
the first distillation.
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