Phosphorus, black colloidal

Colloidal metals are usually prepared by reduction of a salt with a reducing agent, such as phosphorus, acetone, tannin, or carbon monoxide. Platinum metals can also be prepared as finely divided very active blacks by reducing the metal salt in an aqueous solution of sodium or potassium borohydride. 

Wohler obtained phosphorus by strongly heating a mixture of sand and bone-black (calcium phosphate and carbon) — the modern process, now carried out in the electric furnace. He prepared artificial nickel arsenide and worked on the separation of iridium and osmium in a pound of platinum residues given him by Dumas on a visit to Paris in 1833. A supposed silver suboxide, Ag40, prepared by Wohler by the action of caustic potash solution on a supposed subcitrate made by heating silver citrate in hydrogen at 100°, was not analysed and was probably a mixture of silver and silver oxide AggO the red colour of the solution of the subcitrate was probably due to colloidal silver. ... 

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