DERIVATIVES OF DIPIIENOOUINONE. 257 



in hot water to a deep i:)urple colour. Its constitution is. very 

 probably, 



The basic nitrate of the above quinhydrone is obtained as a 

 fine purple precipitate by dissolving 4 grams of tolidine in 

 100 cc N.HXO3 and 400 cc of water and adding just over the 

 theoretical quantity of chromium trioxide (from 30141^16^2+ 

 12 ITNO3+ 2Cr03). The precipitate can be washed despite its 

 gelatinous character, on a Buchner funnel, and has a brilliant 

 copper lustre. Dried over sulphuric acid in vacuo and analysed 

 as above. Found Cr = 0.66% (adventitious) ; H for reduction 

 o.44%;HN03 =8.1%. 



This substance is of the same class as the so-called " benzi- 

 dine chromate,"* which has been shown to be the dichromate of 

 dipheniminoquinhydrone (=benzidine-f-diphenoquinonediimine). 

 The analogous substance in the tolidine series is obtained as 

 above, using excess of potassium chromate instead of CrOs. It 

 is identical in appearance with " benzidine chromate," but blackens 

 on drying owing to some internal oxidation. 



0.6381 gave 0.1498 GraOs — Cr = 16.1% 

 C.2HH3.2N4Cr,207 requires Cr — 16.25% 



The substance is dicresiniiiioqiiijiJiydroiie dichromate. 



The heated substance contains a polymerised base giving a 

 maroon colour with sulphuric acid, instead of the yellow given 

 by the original (presumably the same as the above-mentioned 

 azo-dye). 



E. Dihrouwdicresoquinone (5-5' dibronio- 3-.V diinefhyl- 

 diphenoquinone and its stereoisomer 3-5' dihromo- 3'-5 diinethyl- 

 dipluvwqninone) is obtained by similar methods to tuat described 

 for dicresoquinone, by oxidising 5-5' dibromo-dicresolf in 

 various ways, but the dark variety {presumably the 5-5' dibromo- 

 or as variety) is that generally obtained. By using two parts of 

 dibromodicresol and one part of Cr03 in excess of warm glacial 

 acetic acid and filtering off as soon as the quinone separates, 

 it is obtained in bright scarlet needles with a very faint green 

 metallic lustre, lender the microscope the substance forms com- 

 plex bundles of blood-red needles without extinction. When 

 heated in a melting point tube it decomposes suddenly to a pale 

 substance at 194°. Caustic soda does not affect it until after 

 prolonged exposure, when the beautiful indigo-like sodium salt 



• See Moir: Proc. 1906, 258 and Trans. Roy. Soc. S. Afr., 1911. 

 t Trans. 1907, 1310. 



