HAIR DYES. Various means have been adopted for changing the natural color of the hair to a more favored one, and for hiding the approaches of age, as indicated by the presence of gray hairs. These usually consist in washing the hair with a solution of some metallic salt known to have the effect of darkening its color. These are the salts or oxides of silver, mercury, lead, and bismiith. The :most perfect mode of dyeing the hair, however, is that of previously preparing it by a complete soaking with a solu tion of sulphide of potassium ; the strength of this solution must depend ou the depth of tint intended to be given ; the stronger the solution, the darker the color will be. When thoroughly wetted, the hair is allowed to dry partially ; and whilst still damp, it is to be again thoroughly wetted with a solution of nitrate of silver, also proportioned in strength by the same rule as in the case of the solution first applied. This makes a very permanent dye, which only requires renewing as the new growth of hair becomes conspicuous. The fashion of dyeing the hair is very ancient, and belongs as much to
savage as to civilized nations ; but in the case of the former, vegetable dyes have been chiefly used ; and the ladies of China and other eastern countries also resort to the same: the juice of the petals of hibiscus trionum, the bladder-ketmia, and probably other species of hibiscus, is in general use with them.
The detection of stained hair is sometimes an object of medico-legal investigation. Lead may be detected by boiling the hair in dilute nitric acid, and then applying the tests for lead (q.v.) to the acid solution ; while the presence of silver may be shown by digesting the hair in dilute hydrochloric acid or chlorine water, when the resulting chloride of silver may be dissolved out with a solution of ammonia, and submitted to the ordinary tests' ests for silver (q.v.).