Oils, fats, waxes, and bodies somewhat similar in nature, may--according
to the substance of a paper recently read before the Chemical Society,
by Mr. A. H. Allen, of Sheffield, and Mr. Thomson, of Manchester--be
divided into two great classes, viz., those which combine with soda,
potash, or other alkalies to form soaps, and those which do not; and
as those two classes of bodies differ materially in their actions on
substances such as iron, copper, etc., with which they come in contact,
it often becomes a question of great importance to the users of oils
for lubricating purposes to know what proportions of these different
substances are contained in any oil or mixture of oils. The object of
the authors was to give accurate methods for determining the percentages
of these bodies contained in any sample. Hydrocarbon or mineral oils are
now much used for lubricating the cylinders of engines, and especially
of condensing engines, and that for two reasons--first, because they are
neutral bodies, which have no action on metals; and, second, that they
are not liable to deposit on the boilers, if they should happen to be
introduced with the condensed water so as to produce burning of the
ironwork over the flues.
Animal or vegetable oils or fats are composed of fatty acids in
combination with glycerine, and these, under the influence of
high-pressure steam, are decomposed or dissociated, the fatty acids
being liberated from the glycerine, leaving the former to act upon or
corrode the iron of the cylinder. But here their objectionable influence
does not end. They form with the iron hard, insoluble compounds called
iron soaps, which increase the friction between the cylinder and piston,
and in some cases gradually collect into the form of hard balls inside
the cylinder.
When the water is used over and over again a considerable proportion of
the fatty acids of the oils used for lubricating the piston is carried
over with the steam and is found in the condensed water which is
introduced into the boiler along with the water. Here it commences
action, which proves quite as injurious to the boiler as it does to the
cylinder, but in a different way. It acts upon the iron of the boiler
and on some of the lime salts which constitute the incrustation, forming
greasy iron and lime soaps, which prevent the water from coming into
absolute contact with it. Thus the heat cannot be drawn away quickly
enough by the water, and the plates thus coated above the flues are
liable to become burdened and weakened. This action has in many cases
gone on to such an extent that the flues have collapsed under the
pressure of the steam inside.
The authors give two different processes for the determination of animal
or vegetable oils or fats and hydrocarbon or other neutral oils. They
take a certain weight of the sample and boil it with twice its weight
of an eight per cent, solution of caustic soda in alcohol. The soda
combines with the fatty acids of the animal or vegetable oils forming
soaps; bicarbonate of soda is then added to neutralize the excess of
caustic soda; and, lastly, sand; and the whole is evaporated to dryness
at the temperature of boiling water. The dry mixture is then transferred
to a large glass tube, having a small hole in the bottom plugged with
glass wool to act as a filter, and light petroleum spirit--which boils
at about 150° to 180° Fahr.--is poured over it, till all the neutral or
unsaponifiable oil is dissolved out. In the other process no sand is
used, but the dry mixture is dissolved in water, and the soap solution
which holds the neutral oils in solution is treated with ether, which
dissolves out the neutral oil and then floats to the surface of the
liquid. The ether solution is then drawn off, and the ether in the one
case and petroleum spirit in the other are separated from the dissolved
oils by distillation, the last traces of these volatile liquids being
separated by blowing a current of filtered air through the flask
containing the neutral oil, which is then weighed and its percentage on
the original sample calculated.
All animal and vegetable oils yield a small quantity--about one per
cent.--of unsaponifiable fatty matter, which must be deducted from the
result obtained. Sperm oil, however, was found to be an exception,
because from its peculiar chemical constitution it yields nearly half
its weight of a greasy substance to the ether or to the petroleum
spirit. The substance, however, dissolved from sperm oil after
saponification has the appearance of jelly, when the ether or petroleum
spirit solution is concentrated and allowed to cool, and the presence of
sperm oil can thus be readily detected. Solid paraffin, heavy petroleum
or paraffin oils, and rosin oil--which is produced by the destructive
distillation of rosin--are not saponifiable, and yield about the whole
of the amount employed to the petroleum spirit or ether. Japan wax is
almost entirely saponifiable, while beeswax and spermaceti yield about
half their weights to the petroleum spirit or ether.
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