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SOME EEMAEKABLE OXIDATION-PEODUCTS OF 
BENZIDINE. 
By James Mom, M.A., D.Sc, F.C.S., F.R.S.S.Af. 
(Read March 15, 1911.) 
The two substances discussed in this paper are prepared by oxidising 
benzidine with chromic acid and with potassium ferricyanide respectively, 
and their formation has long been known, the reactions indeed serving as 
the best tests for benzidine in nearly neutral solution. The two substances 
closely resemble indigo in appearance— very dark-blue needles, insoluble 
in all solvents except strong mineral acids, and possessing a distinct 
coppery reflex ; nevertheless, they are described in the literature 
as simple chromate and ferricyanide of benzidine, on the authority of 
their respective discoverers, viz., Julius {Monatshefte, 1884, p. 192, also 
Sitzungsber. 1884, p. 78) and Barzilowsky [Journ. Buss, cliem. Ges., 17, 
p. 366). 
It is, of course, obvious nowadays that a colourless base must give a 
yelloiv chromate and ferricyanide, and that therefore these dark- blue 
substances must be salts of an oxidation-product of benzidine. Curiously 
enough, Julius considered this possibility and rejected it. He found on 
treating the blue chromate v^ith ammonia, that he recovered a small 
quantity of benzidine. The present author finds that this is the case only 
when the blue substance has been obtained under circumstances where 
the chromic acid has not had full scope for oxidation (viz., cold dilute 
nearly neutral solutions), and that even then the amount of benzidine 
recovered is an insignificant fraction of that originally taken. On the 
other hand, when a benzidine hydrochloride solution is slowly added to 
bichromate solution at about 40°, and after 20 minutes or so, the blue 
paste is decomposed, in the liquid, with caustic soda, the resultant product 
is wholly a chestnut-brown base, free from benzidme. 
The investigation both of the original blue substance and of the base is 
rendered very difficult by their reactivity, but so far as the author can see 
the base appears to be a hydrated form of diphenoquinonediimine, of which 
the anhydrous form was obtained by Willstatter and Kalb {Berich., 1905, 
