l purposes and consisting essentially of ordinary boiled soap
to which additions of various substances have been made.

With additions of naphtha, fractions of petroleum, and turpentine, the
detergent power of the soap is increased by the action of these
substances in removing grease.

Amongst the many other additions may be mentioned: ox-gall or
derivatives therefrom (for carpet-cleaning soap), alkali sulphides (for
use of lead-workers), aniline colours (for home-dyeing soaps), pumice
and tripoli (motorists' soaps), pine-needle oil, in some instances
together with lanoline (for massage soaps), pearl-ash (for soap intended
to remove oil and tar stains), magnesia, rouge, ammonium carbonate,
chalk (silversmiths' soap), powdered orris, precipitated chalk,
magnesium carbonate (tooth soaps).

Soap powders or dry soaps are powdered mixtures of soap, soda ash, or
soda crystals, and other chemicals, whilst polishing soaps often contain
from 85 to 90 per cent. siliceous matter, and can scarcely be termed
soap.

CHAPTER VIII.

SOAP PERFUMES.

_Essential Oils--Source and Preparation--Properties--Artificial
and Synthetic Perfumes._

The number of raw materials, both natural and artificial, at the
disposal of the perfumer, has increased so enormously during recent
years that the scenting of soaps has now become an art requiring very
considerable skill, and a thorough knowledge of the products to be
handled. Not only does the all-important question of odour come into
consideration, but the action of the perfumes on the soap, and on each
other, has also to be taken into account. Thus, many essential oils and
synthetic perfumes cause the soap to darken rapidly on keeping, _e.g._,
clove oil, cassia oil, heliotropin, vanillin. Further, some odoriferous
substances, from their chemical nature, are incompatible with soap, and
soon decompose any soap to which they are added, while in a few cases,
the blending of two unsuitable perfumes results, by mutual reaction, in
the effect of each being lost. In the case of oils like bergamot oil,
the odour value of which depends chiefly on their ester content, it is
very important that these should not be added to soaps containing much
free alkali, as these esters are readily decomposed thereby. Some
perfumes possess the property of helping the soap to retain other and
more delicate odours considerably longer than would otherwise be
possible. Such perfumes are known as "fixin