The color of oil is usually pure black. Sometimes it varies in brown-brown tones (from dirty yellow to dark brown, almost black), occasionally there is oil colored in a light yellow-green color, and even colorless, as well as rich green oil[12][13]. It has a specific smell, also varying from lightly pleasant to heavy and very unpleasant. The color and odor of oil are largely due to the presence of components containing nitrogen, sulfur and oxygen and are concentrated in the lubricating oil and petroleum residue. Most petroleum hydrocarbons (except aromatic ones) in their pure form are odorless and colorless[14].
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