Ferrous thio-pyrophosphite, Fe₂P₂S₆

Ferrous thio-pyrophosphite, Fe₂P₂S₆, has been obtained by heating a mixture of sulphur and red phosphorus with excess of iron wire to redness and maintaining at this temperature for several hours. It yields greyish black hexagonal plates which appear brown by transmitted light. They are attacked by nitric acid, but more easily by this acid containing a little potassium chlorate.