Chemistry Reference
In-Depth Information
Soap is formed when an alkaline solution that include salts of sodium
or potassium reacts with a fat or an oil, in a chemical reaction known as
saponification
. Soap has been made since antiquity by the saponification of
animal fat or vegetable oil with some alkaline substance such as wood ash,
soda, or potash. One of the earliest formal accounts of making soap was
written on Sumerian clay tablets from the midthird millennium B.C.E. and
the writings disclose the making of soap from cassia oil, ash, and water. Clay
cylinders containing a soaplike substance found in Babylon probably
provide evidence that soapmaking may have being practiced there at even
earlier times, during the early third millennium B.C.E. Inscriptions on the
cylinders explain that the contents of the cylinders were made by boiling
fat mixed with ash, a method of making soap that is practiced to this day.
Pliny, the first-century C.E. Roman author of an encyclopedic natural history,
described the process of making soap from goat's tallow and wood ash.
It is quite probable that in antiquity soap was used only for cleansing
cloth and garments and for the treatment of disease, but not necessarily
for personal cleanliness. Galen, a second-century C.E. Greek physician, for
example, recommended bathing with soap for some skin conditions. The use
of soap for personal cleanliness apparently became relatively widespread
only during the late Roman Empire; as late as the eighteenth century in many
places of the world however bathing was considered an oddity, not the
norm.
