ismuth, have been blended by
heat and careful trituration, has generally a like effect on the hair
to ferruginous solutions; so also has a leaden comb, but its action is
very uncertain. None of these last are, however, safe for
long-continued use. Atrophy of the scalp, baldness, and even local
paralysis, have sometimes, though rarely, been caused by them.

When the normal sulphur of the hair is absent, or deficient, the
preceding substances fail to darken the hair. In this case the desired
effect may often be produced by also moistening the head, say twice a
week, with water, to which a little sulphuret of potassium or
hydrosulphuret of ammonia has been added.

When it is desired to dye or darken the hair more rapidly, as in a few
hours, or even a few minutes, plumbite of lime, plumbite of potassa,
or nitrate or ammonia--nitrate of silver--is usually employed. The
first is commonly produced by the admixture of quicklime with oxide of
lead (litharge), carbonate of lead, or acetate of lead. These
ingredients should be in appropriate proportions, but very generally
the reverse is the case in those of the shops.

It may be laid down as a rule that when the lime is in greater
proportion than about two to one of the oxide, and to the
corresponding equivalents of the other substances mentioned, or when
the lime has not been prepared in a proper manner, the compound is not
safe, and very likely to prove injurious to the skin and hair-bulbs,
and perhaps to act as a depilatory. The effects of these lead dyes
arise partly in the way previously described and partly by direct
chemical action between the sulphur of the hair and the lead which
they contain, sulphuret of lead being formed in the surfacial portion
of the hair. It is on the last that their more immediate effect
depends. If there be no sulphur in the hair, they will not darken it.
After the necessary period of contact, they should be gently but
thoroughly removed from the hair and skin by rubbing them off with the
fingers, and by the use of the hairbrush, the head being then washed
clean with tepid water. Should the tint imparted by them not be deep
enough, or be too fiery, it may be darkened and turned on the brown or
black by moistening the hair the next day with a very weak solution of
sulphuret of potassium, or of hydrosulphuret of ammonia.

None of the compounds of lead stain the skin, an advantage which has
led to a preference being given to them by many persons