OILS, FATS, AND SOAPS.
313. Sources and Kinds of Oils and Fats.--Oils and fats are
insoluble in water; the former are liquid, the latter solid. Most
fats are obtained from animals, oils from both plants and
animals. Oils are classified as fixed and essential. Castor oil
is an example of the former and oil of cloves of the latter.
Fixed oils include drying and non-drying oils. They leave a stain
on paper, while essential, or volatile oils, leave no trace, but
evaporate readily. Essential oils dissolved in alcohol furnish
essences. They are obtained by distilling with water the leaves,
petals, etc., of plants. Drying oils, as linseed, absorb O from
the air, and thus solidify. Non-drying ones, as olive, do not
solidify, but develop acids and become rancid after some time.
Oils and fats are salts of fatty acids and the base glycerin. The
three most common of these salts are olein, found in olive oil,
palmitin, in palm oil and human fat, and stearin, in lard. The
first is liquid, the second semi-solid, the last solid. Most fats
are mixtures of these and other salts.
Olefin = Glyceryl) ( oleic)
oleate ) ( )
Pahnitin = Glyceryl)salts from (palmitic)acid and glyceryl hydrate.
palmitate) ( )
Stearin = Glyceryl) (stearic )
stearate)
314. Saponification consists in separating these salts
into their acids and the base glycerin; soap-making is the best
illustration. To effect this separation, a strong soluble base is
used, KOH for soft, and NaOH for hard soap. Study this reaction:
Glyceryl oleate ) (sodium ) (oleate )
Glyceryl palmitate) + (hydrate) = sodium (palmitate) + (glyceryl
Glyceryl stearate ) (stearate ) (hydrate
Soaps are thus salts of fatty acids and of K or Na.
315. Soap is soluble in soft water, but the sodium stearate
probably unites with water to form hydrogen sodium stearate and
NaOH. The grease which exudes from the skin, or appears in
fabrics to be washed, is attacked by this NaOH and removed,
together with the suspended dirt, and a new soap is formed and
dissolved in the water. Hard water contains salts of Ca and Mg,
and when soap is used with it the Na is at once replaced by these
metals, and insoluble Ca or Mg soaps are formed. Hence in hard
water soap will not cleanse till all the Ca and Mg compounds have
combined.
316. Glycerin, C3H5(OH)3, is a sweet, thick, colorless, unctuous
liquid, used in cosmetics, unguents, pomades, etc. It is prepared
in quantity by passing superheated steam over fats when under
pressure.
317. Dynamite.--Treated with HNO3 and H2SO4 glycerin forms the
very explosive and poisonous liquid nitro-glycerin. In this
process the C3H5(OH)3 becomes C3H5(NO3)3. C3H5(OH)3 + 3HNO3 =
C3H5(NO3)3+3 H2O. H2SO4 is used to absorb the H2O which is
formed. Nitro-glycerin, absorbed by gunpowder, diatomaceous
earth, sawdust, etc., forms dynamite. For obvious reasons the
pupil should not experiment with these substances.
318. Butter and Oleomargarine.--Milk contains minute particles of
fat, about 1/500 of an inch in diameter, which give it the
whitecolor. These particles are lighter than the containing
liquid, and rise to the top as cream. Churning unites the
particles more closely, and separates them from the buttermilk.
The flavor of butter is due to the presence of five or ten per
cent of butyric and other acids of the same series.
It was found that cows gave milk after they ceased to have food;
hence it was inferred that the milk was produced at the expense
of the cows' fat. Why could not butter be artificially made from
the same fat? It was but a step from fat to milk, as it was from
milk to butter. Oleomargarine, or butterine, was the result. Beef
fat, suet, is washed in water, ground to a pulp, and partially
melted and strained, the stearin is separated from the filtered
liquid and made into soap, and an oily liquid is left. This is
salted, colored with annotto, mixed with a certain portion of
milk, and churned. The product is scarcely distinguishable from
butter, and is chemically nearly identical with it, though less
likely to become rancid from the absence of certain fatty acids;
its cost is perhaps one-third as much as that of butter.