be to add the soda salt of the acid to soap.

Amongst the more common milled medicated toilet soaps may be mentioned,
in addition to the above:--

_Birch Tar Soap_, containing 5 or 10 per cent. birch tar, which has a
characteristic pungent odour and is recommended as a remedy for eczema
and psoriasis.

_Carbolic Soap._--A toilet soap should not contain more than 3 per cent.
of pure phenol, for with larger quantities irritation is likely to be
experienced by susceptible skins.

_Coal Tar._--These soaps contain, in addition to carbolic acid and its
homologues, naphthalene and other hydrocarbons derived from coal,
naphthol, bases, etc. Various blends of different fractions of coal tar
are used, but the most valuable constituents from a disinfectant point
of view are undoubtedly the phenols, or tar acids, though in this case
as with carbolic and cresylic soaps, the amount of phenols should not
exceed 3 per cent. in a toilet soap. An excess of naphthalene should
also be avoided, since, on account of its strong odour, soaps containing
much of it are unpopular. The odour of coal tar is considerably modified
by and blends well with a perfume containing oils of cassia, lavender,
spike, and red thyme.

_Formaldehyde._--This substance is one of the most powerful
disinfectants known, and it may be readily introduced into soap without
undergoing any decomposition, by milling in 2-3 per cent. of formalin, a
40 per cent. aqueous solution of formaldehyde, which is a gas. White
soaps containing this chemical retain their whiteness almost
indefinitely.

New combinations of formaldehyde with other bodies are constantly being
brought forward as disinfectants. Among others the compound resulting
from heating lanoline with formaldehyde has been patented (Eng. Pat.
7,169, 1898), and is recommended as an antiseptic medicament for
incorporation with soap.

_Glycerine._--Nearly all soaps contain a small quantity of this body
which is not separated in the lyes. In some cases, however, a much
larger quantity is desired, up to some 6 or 8 per cent. To mill this in
requires great care, otherwise the soap tends to blister during
compression. The best way is to dry the soap somewhat further than
usual, till it contains say only 9 or 10 per cent. moisture and then
mill in the glycerine.

_Ichthyol_ or _Ammonium-Ichthyol-Sulphonate_ is prepared by treating
with sulphuric acid, and afterwards with ammonia, the hydrocarbon oil
containing sulphu