Liver of sulfur

Liver of sulfur can be created by reacting potassium carbonate (traditionally called pearlash) with an excess of elemental sulfur in an oxygenated environment. The sulfur disproportionates and the resulting compounds include potassium thiosulfate, an oxidising agent, and potassium sulfide. When exposed to air and light, it tends to decompose over time to potassium carbonate and potassium sulfate, neither of which has any oxidizing power. In the traditional view, no redox occurs in this reaction, but experimental evidence regarding the oxidation states of sulfur in thiosulfate ions indicates that the sulfur experience further redox disproportionation in this reaction, from oxidation states of −1 and +5 to −2 and +6. : 4 K2CO3 + 6/8 S8 + O2 → 2 K2S2O3·K2S + 4 CO2 : 1/8 S8 + O2 → SO2 : ==Physical properties==

It is sold as a yellow brittle solid (a "lump" which must be mixed with water before use) as well as a pre-mixed liquid and a gel form. The solid is believed to have the longest shelf life, though all liver of sulfur tends to decompose with time. Modern gel forms contain stabilizers that allow the reactivity to last much longer. Liver of sulfur that is kept dry, sealed from air, out of the light, and in a freezer will last many times longer than that kept in any other condition. The highest quality liver of sulfur in solid form is a dark yellow, almost "liver" colored substance. As it ages and is exposed to air, its potency decreases, it will turn lighter yellow and finally white, at which point it has fully decomposed to a form with negligible reactivity. ==Usage==

Metalworking Liver of sulfur is mainly used in metalworking to form a brown or black patina on copper and silver as well as many (though not all) copper alloys and silver alloys (brass, for example— a copper alloy— does not react with sulfur compounds). As it ages and is exposed to air, it increasingly decomposes to sulfate of potash and carbonate of potash, neither of which has any value as an oxidizer of metal. At one time sulfurated potash was used to combat arthritis. It eventually fell into disfavor for medical purposes because sulfides and polysulfides were discovered to be toxic in their own right. ==References==