Ichthyol
Ammonium bituminosulfonate or ammonium bituminosulphonate (synonyms of ichthammol, CAS#8029-68-3 brand name: Ichthyol) is a product of natural origin obtained in the first step by dry distillation of sulfur-rich oil shale (bituminous schists). By sulfonation of the resulting oil (or purified fractions thereof) and subsequent neutralization with ammonia, Ichthammol results as viscous, water-soluble substance with characteristic bitumen-like odor. It is used in medicine as a treatment for different skin diseases, including eczema and psoriasis (see below). Ointments containing 10% or 20% Ichthammol are most common. They are sometimes called "black ointments" or "drawing salves". Ichthammol's dermatological action was promoted by German physician Paul Gerson Unna.
From elemental analysis, its composition was calculated to be C28H36S5O6(NH4)2. However, as a product of natural origin, it is a mixture of many different compounds.
Chemically, it is a sulfonated shale oil that is incompatible with acids, alkali carbonates or hydrates and alkaloidal salts. It is a thick reddish brown liquid, possessing a bituminous odor and taste. It is soluble in water and miscible with glycerin, but is nearly insoluble in strong alcohol or concentrated ether. It contains a large percentage of organically combined sulfur.
Materials made in China (Pinyin transcription: yushizhi and yushizhi ruangao) and offered outside China as Ichthammol or Ammonium Bituminosulfonate are not in line with the definition given for this substance in the United States Pharmacopoeia (USP) or European Pharmacopoeia (Ph.Eur). Also, there is no conformity with the definition as connected to CAS# 8029-68-3. The Chinese material is derived from vegetable oils (e.g. soybean oil) instead of bituminous schists as required. As a result, its chemical basis is totally different from the one of Ichthammol USP/Ph.Eur./CAS# 8029-68-3. The characteristic bitumen-like odor (originating from the bituminous source material) is missing with Chinese material and thereby the original qualities according to common standards can be identified without doubt.
...
Wikipedia