This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
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.
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.