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 deg. to 180 deg. Fahr.--is poured over it, till all the
neutral or unsaponifiable oil is dissolved out.
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