e with extremely satisfactory results. Strengths of
1/2, 1, and 3 per cent. biniodide are sold, but owing to the readiness
with which it is absorbed by the skin a soap containing more than 1/2
per cent. should only be used under medical advice.

A similar combination of _bromide of mercury_ with potassium, sodium, or
ammonium bromide has recently been patented by Cooke for admixture with
liquid, hard, or soft soaps.

_Zinc and other Metallic Salts._--At various times salts of metals other
than mercury have been added to soap, but, owing to their insolubility
in water, their efficiency as medicaments is very trifling or nil.
Compounds have been formed of metallic oxides and other salts with oleic
said, and mixtures made with vaseline and lanoline, and incorporated
with soap, but they have not met with much success.

Another chemical commonly added to soap is _Borax_. In view of its
alkaline reaction to litmus, turning red litmus blue, this salt is no
doubt generally regarded as alkaline, and, as such, without action on
soap. On the contrary, however, it is an acid salt containing an excess
of boric acid over the soda present, hence when it is added to soap,
fatty acids are necessarily liberated, causing the soap to quickly
become rancid. As a remedy for this it has been proposed to add
sufficient alkali to convert the borax into neutral mono-borate of soda
which is then added to the soap. This process is patented and the name
"Kastilis" has been given to the neutral salt. The incorporation of
borax with the addition of gum tragasol forms the subject of two patents
(Eng. Pats. 4,415, 1904; and 25,425, 1905); increased detergent and
lasting properties are claimed for the soap. Another patented process
(Eng. Pat. 17,218, 1904) consists of coating the borax with a protective
layer of fat or wax before adding to the soap with the idea that
reaction will not take place until required. _Boric acid_ possesses the
defects of borax in a greater degree, and would, of course, simply form
sodium borate with liberation of fatty acids, so should never be added
to a neutral soap.

_Salicylic Acid_ is often recommended for certain skin diseases, and
here again the addition of the acid to soap under ordinary conditions
results in the formation of sodium salicylate and free fatty acids.

To overcome this a process has recently been patented for rubbing the
acid up with vaseline before addition to soap, but the simplest way
appears to