Butter of Tin

Tin tetrachloride or stannic chloride is a chemical compound with the formula SnCl4. At room temperature it is a colourless liquid, which fumes on contact with air, giving a stinging odour. It is prepared from reaction of chlorine gas with elemental tin.

Sn + 2 Cl2 → SnCl4

It was used as a chemical weapon in World War I, as it formed an irritating (but non-deadly) dense smoke on contact with air: it was substituted for by a mixture of silicon tetrachloride and titanium tetrachloride near the end of the War due to shortages of tin. It is also used in the glass container industry for making an external coating containing tin(IV) oxide which toughens the glass.