OXIDATION PRODUCTS OF DIANISIDINE. 165 



A more basic salt of lighter purple colour and with copper- 

 coloured metallic lustre is obtainable by using- sodium acetate 

 after the addition of FeCl.^ in the preparation, or by o])erating- on 

 a diluted alcoholic solution of dianisidine (the base) with nearly 

 neutral FeCl^. This variety is very slimy and unfilterable, and is 

 best freed from iron by washing with very dilute acetic acid, in 

 which it is practically insoluble : it gives a bright bluish-green 

 colour when rubbed on a white surface so as to give a thin layer. 

 The coloration given by concentrated sulphuric acid with both of 

 these hydrochlorides is garnet-red, which is orange when diluted, 

 and quite stable even on great dilution. 



The parent substance from the action of FeCl;. on benzidine, 

 diplicniuiiuoquinhydronc, gives a pure orange colour.''- 



The most remarkable property of these blue salts should be 

 mentioned here, viz., the isomeric change induced by alkalis. Any 

 alkali, even tap water, produces a chestnut-brown precipitate of 

 an insoluble base which on treating with acids gives salts entirely 

 dififerent from the above quinhydronic salts : with very dilute 

 acids the solutions of the new salts are brownish orange : stronger 

 acids give olive-green solutions: still more acid gives a wine-red 

 colour : quite strong acids give an intense and beautiful crimson 

 purple: on dr)nng up an acid solution of the chestnut base, these 

 colours appear in rings edging the vessel. In the solid state the 

 HCl-compound of the isomerised chestnut base is dull olive and 

 almost without lustre. Concentrated sulphuric acid gives an intense 

 crimson-purple shade with traces of the isomeric base. The crude 

 chestnut base melts easily and contains free dianisidine which, 

 can be removed by hot dilute alcohol, and the undissolved base, 

 which melts at about 220° (not sharp) and should be dianisiniiiio- 

 quinone, is in reality a polymer thereof of azo-dye nature, viz., 

 NH.XeH.OMe.Q.H^OMe.N :N.C,H,OMe.QH3. OMe.NH,. 



This follows from the fact that the substance is difficult to 

 reduce by hot stannous chloride and then yields dianisidine. 

 whereas the original quinhydronic substance is immediately 

 reduced in the cold. 



(2) Hydrohromide of the quinhydrone. — 15 grams dianisi- 

 dine in excess of cold 1% HBr solution is treated with 30 cc 

 liquor ferri percMor. fort. B.P. previously mixed with 100 grams 

 of potassium bromide in saturated solution. The purple hydro- 

 bromide is filtered off after standing twenty minutes (not longer), 

 and being well crystallized, can be properly washed out, if only 

 small quantities of wash water are used at a time, since hydrolysis 

 occurs as the acid is removed. The quinhydronic hydrohromide 

 forms a magnificent purple paste with brilliant copper lustre on 

 rubbing: it is blue-green by transmitted light, but in mass the 

 coppery lustre causes it to appear purple. The solution in slightly 

 acid water is blood-red, and on dilution greenish blue. In abso- 

 lutely neutral water the colour is at first dull red, after some 

 time changing through olive to green, the latter stage being 



* See Trans. Roy. Soc. S. Afr., p. 209. 



