929, REPORT—1904. 
isomerides. Thus it is noteworthy that the earliest indication of the 
possible existence of hydroxylic pseudonitro compounds was based upon 
observations of colour-change, and the suggestion made by Armstrong 
in 1892,! in order to account for the coloured salts of the nitrophenols, 
has been abundantly justified by the subsequent investigations of Nef, 
Hantzsch, and others. According to this view the colourless ethers 
have formule of the type EtO.C;H,.NO,, whilst the coloured salts are 
formulated as O:C,H,:NO,K ; in the liquid state the nitrophenols 
themselves may exist in both forms, 
HO.C,H,.NO,50 : C,H, : NO,H, 
but the colourless needles of p-nitrophenol must be represented by the 
first, and the quinone-like crystals of o-nitrophenol by the second 
formula. 
Again, of the compounds represented by the formulee— 
NH 
(1) HO.C,H,NO (2) 0: C,H,: NOH (3) O: CHL | 
6 
the first should be blue or green like the o and p ethers, MeO.C,H,.NO ;* 
the second should be red like the sodium salt, O:C,;H,: NONa, or 
yellow like the benzoyl- derivative O: C,H, : NOBz, whilst the third 
should be colourless like the pseudoquinols. The substance produced by 
the action of nitrous acid on phenol or of hydroxylamine on quinone 
separates from ether in green flakes, and gives a green solution in water, 
alcohol, or ether, which must contain at least a considerable proportion 
of the nitroso- compound (1); the colourless needles which separate 
from aqueous solution may be a dimolecular form of the nitroso- 
compound (p. 224), but must otherwise be represented by the third 
formula. 
The difference in colour between the yellow hydroximes and the 
colourless pseudoximes, observed by Dr. Whiteley in the derivatives of 
isonitrosomalonamide, has already been referred to ; a similar explanation 
may be given of the colour-changes observed in violuric acid and its 
salts (Hantzsch and Isherwood), 
and in ethylic isonitrosocyanacetate and its salts * 
NH 
HON : C(CN).CO,Et Aes DO(EN).COLEt 5 
Qe 
in each case, however, the authors regard the coloured compounds as 
—C—O 
containing the group | | though this group would scarcely be 
—C—N.OH, 
likely to give rise to colour. 
8. Absorption Spectra.—Whilst valuable results are obtained by 
merely noting the colour of dynamic isomerides, data of much greater 
1 Proc. Chem. Soc. 8, 101. 2 Baeyer and Knorr, Ber. 1902, 85, 3034. 
3 Miiller, Bull. Soc. Chim. 1902, iii. 27, 1019. 
