PYROCATECHIN. 305 



potassa-ley, in contact with the air, is rapidly converted 

 into yellow potassium euthiochronate,C\0 2 ) j (92 OIO 2 ~*~ 

 2H 2 0. 



(OH 

 Thiochronic acid, C 6 ^ O.(S0 2 .OH) The yellow 



( (S0 2 .OH) 4 . 



potassium salt, C 6 (OH)0(S0 2 .OE:) 5 + 4H 2 0, is formed, 

 together with potassium dichlordisulphohydroquino- 

 nate, on adding chloranile to a warm solution of potas- 

 sium bisulphite or sulphite. Boiled with hydrochloric 

 acid, and heated with water at 130-140, it is resolved 

 into potassium bisulphate and potassium p-disulpho- 

 hydroquinonate C 6 H 2 (OH) 2 (S0 2 .OK) 2 + 4H 2 0. The free 

 acid, isolated from the latter salt, crystallizes in deliques- 

 cent, thick plates. It is isomeric with the disulpho- 

 hydroquinonic acid described above. 



b. Pyrocatechin (Meta-dioxybenzene, Oxyphenic 

 acid). Is contained in the leaves of Ampelopsis hede- 

 racea. Is produced by the destructive distillation of 

 morintannic, catechuic, protocatechuic, and oxysali- 

 cylic acids, and a number of vegetable extracts (catechu, 

 kino, etc.). Is furthermore formed from metaiodo- 

 phenol (p. 293) and metasulphophenolic acid (p. 295) 

 by fusing with caustic potassa; and by heating cellu- 

 lose and other hydrocarbons for a long time with 

 water at 200. Crystallizes in quadratic prisms, that 

 are easily soluble in water, alcohol, and ether. Fuses 

 at 112 ; sublimes in colorless, shiny laminse ; and boils 

 without decomposition at 240-245. The aqueous solu- 

 tion is colored dark green by iron chloride, and then 

 turns purple on the addition of sodium bicarbonate or 

 tartaric acid, or ammonia. 



Guaiacol (Pyrocatechin-monomethylether), C 7 H 8 2 = 

 C 6 II 4 1 Qpj Is produced by heating equal molecules 



of pvrocatechin, potassium hydroxide, and potassium 



26* 



