The solution of coal tar is prepared as follows:
After mixing the coal tar with 700 cc. of alcohol, add the quillaia and macerate the mixture during seven days in a closed vessel, with occasional agitation. Then filter, and wash the contents of the filter with a quantity of alcohol sufficient to make the product measure 1,000 Gm. or ec.
The procedure described is an unpleasant, time-consuming and labor-consuming process which yields variable results. The color of the product differs according to the origin of the tar as well as in the same tar. In spite of care, small particles of pitch frequently pass through the filter and are objectionable to the patient, especially when the compound is used on light-colored hair. For example, blondes often object to the brown color of scalp lotions containing coal tar solution. Because ethyl alcohol is used in the extraction, the cost of the
BUTTERWORTH T. SYNTHETIC COAL TAR SOLUTION. Arch Derm Syphilol. 1950;61(4):678–679. doi:10.1001/archderm.1950.01530110144016