Asphalt is a hydrophobic material. It is impermeable and almost insoluble in water, acetone, ether and dilute ethanol. It is soluble in carbon disulfide, carbon tetrachloride and sodium hydroxide. Asphalt and its smoke are irritating, phototoxic and carcinogenic to skin and mucosa.
Coal tar pitch is a by-product of coking, that is, the black substance remaining in the distillation kettle after distillation of tar. It differs from refined tar only in physical properties and has no obvious boundaries. The general classification method is to specify that the softening point is tar below 26.7 ("cubic block method") and asphalt above 26.7 ("cubic block method").
Petroleum asphalt is the residue of crude oil distillation. According to the degree of refining, it will be liquid, semi-solid or solid at room temperature. Petroleum asphalt is black and lustrous with high temperature sensitivity. Because it has been distilled over 400 C in the production process, it contains very little volatile components, but there may still be high molecular hydrocarbons that have not been volatilized, which are more or less harmful to human health.