Pyrophorus powders

Col mono cl crysts, sol in w. Its anhydrous salt, KAl(S04)a, mw 258.19, d 2.75 at 20°, when heated with carbon produces "Homberg s Pyrophorus, a flammable compd contg K sulfide(Ref 3). It has also been used in expls, such as Clark s Powder(qv)... 

Pyrophorus. This U a term given to Hubstances which inflame spemtane-ously when exposed to the air. When a small quantity of any of the powders given below is exposed to the air, it rapidly becomes hot and inflames. Their action is quicker in a damp atmosphere, or by the moisture of the breath. 

Self-flammable lead powder can be made by heating certain organic salts alone if care is taken to exclude air. Michael Faraday (1791 — 1867), in a delightful little volume of lectures, describes the lead pyrophorus made by heating dry tartrate of lead in a glass tube closed at one end and drawn to a fine point at the other and then sealed. On breaking the point and shaking out the powder, he demonstrated to his juvenile auditory how the finely divided lead burned with a red flash. 

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