In 1865, the first U.S. patent
for a liquid soap was issued to William Sheppard of New York City (No. 49,561).
The patent described his "discovery that by the addition of comparatively
small quantities of common soap to a large quantity of spirits of ammonia or hartshorn
is thickened to the consistency of molasses, and a liquid soap is obtained of
superior detergent qualities." The proportions given were to dissolve one
pound of common soap in water or steam, and then add 100-lbs of ammonia such
that the liquid thickens to the consistency of molasses. The product was
expected to be useful for both domestic and manufacturing purposes. (Hartshorn
is an ancient name for an aqueous solution of ammonia).
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| Decorative soaps, by Phanton at English Wikipedia (Transferred from en.wikipedia to Commons.) [Public domain], via Wikimedia Commons |
So, how does soap clean?
Action of soap
When used for cleaning, soap
allows insoluble particles to become soluble in water, so they can then be
rinsed away. For example: oil/fat is insoluble in water, but when a couple of
drops of dish soap are added to the mixture, the oil/fat dissolves in the
water. The insoluble oil/fat molecules become associated inside micelles, tiny
spheres formed from soap molecules with polar hydrophilic (water-attracting)
groups on the outside and encasing a lipophilic (fat-attracting) pocket, which
shields the oil/fat molecules from the water making it soluble. Anything that
is soluble will be washed away with the water.
Effect of the alkali
The type of alkali metal used
determines the kind of soap product. Sodium soaps, prepared from sodium
hydroxide, are firm, whereas potassium soaps, derived from potassium hydroxide,
are softer or often liquid. Historically, potassium hydroxide was extracted
from the ashes of bracken or other plants. Lithium soaps also tend to be
hard—these are used exclusively in greases.
Effects of fats
Soaps are derivatives of fatty
acids. Traditionally they have been made from triglycerides (oils and fats).
Triglyceride is the chemical name for the triesters of fatty acids and
glycerin. Tallow, i.e., rendered beef fat, is the most available triglyceride
from animals. Its saponified product is called sodium tallowate. Typical
vegetable oils used in soap making are palm oil, coconut oil, olive oil, and
laurel oil. Each species offers quite different fatty acid content and hence,
results in soaps of distinct feel. The seed oils give softer but milder soaps.
Soap made from pure olive oil is sometimes called Castile soap or Marseille
soap, and is reputed for being extra mild. The term "Castile" is also
sometimes applied to soaps from a mixture of oils, but a high percentage of
olive oil.
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