the most suitable for the purpose, but in practice found that the best
results were obtained by using a superfatted soap made from a blend of
one part of olive oil with eight parts of beef tallow, saponified with a
mixture of two parts of soda to one part of potash, sufficient fat being
employed to leave an excess of 3 or 4 per cent. unsaponified. Recent
researches have shown, however, that even if a superfatted soap-base is
beneficial for the preparation of toilet soaps (a point which is open to
doubt), it is quite inadmissible for the manufacture of germicidal and
disinfectant soaps, the bactericidal efficiency of which is much
restricted by the presence of free fat.

Many of the medicaments added to soaps require special methods of
incorporation therein, as they otherwise react with the soap and
decompose it, forming comparatively inert compounds. This applies
particularly to salts of mercury, such as _corrosive sublimate_ or
mercuric chloride, and _biniodide of mercury_, both of which have very
considerable germicidal power, and are consequently frequently added to
soaps. If simply mixed with the soap in the mill, reaction very quickly
takes place between the mercury salt and the soap, with formation of the
insoluble mercury compounds of the fatty acids, a change which can be
readily seen to occur in such a soap by the rapid development on
keeping, of a dull slaty-green appearance. Numerous processes have been
suggested, and in some cases patented, to overcome this difficulty. In
the case of corrosive sublimate, Geissler suggested that the soap to
which this reagent is to be added should contain an excess of fatty
acids, and would thereby be rendered stable. This salt has also been
incorporated with milled soap in a dry state in conjunction with
ammonio-mercuric chloride, [beta]-naphthol, methyl salicylate, and
eucalyptol. It is claimed that these bodies are present in an unchanged
condition, and become active when the soap is added to water as in
washing. Ehrhardt (Eng. Pat. 2,407, 1898) patented a method of making
antiseptic mercury soap by using mercury albuminate--a combination of
mercuric chloride and casein, which is soluble in alkali, and added to
the soap in an alkaline solution.

With biniodide of mercury the interaction can be readily obviated by
adding to the biniodide of mercury an equal weight of potassium iodide.
This process, devised and patented by J. Thomson in 1886, has been
worked since that tim