Colour and Chemical Cohstitntion. 
209 
For the former substance, calculation gives CCO + 2C0C = 94 + 206 = 300 ; 
for the latter we have CCN + 2CCC = 98 + 206 = 304. The observed values 
are both about X 290 (Tuck, J.C.S., 1909). It is to be noted that free 
phenol and aniline hydrochloride give entirely different spectra, which 
cannot be calculated. 
(9) Sodium paraoxyhenzaldeliyde. 
This is 
^CH-CH-,;--.. ^ 
o=cH-c(....-- ;c-o^ 
♦ CH-CH 
in which, as before, the non-tautomeric double bond is not shown. This 
consists of the tautomerisms CCO + CCC + CCO loaded with the ring 
residue - CH - CH - . The calculated figure is therefore 94+103 + 94 + 
22 = 313. The observed figure in alcohol) is about X 330 (Baly, J.C.S., 
1907). The substance is colourless. 
(10) Sodium salicylaldehyde. 
This is yellow because the tautomerism goes right round the ring : 
.•■jcH-'CH^ 
HCv ••v<C-.0^ 
^CH =• c:; 
■•>cn=p 
It consists of CCO + CCC + CCC + CCO, and the calculated figure is : 
2x94 + 2x 103 = 394. Baly observed X 388 (l.c). 
At this stage we will now consider the three symmetrical aniline dyes, 
aurine, parafuchsine and crystal-violet, which have always been a puzzle 
to the colour chemist because their colours are lower than those of the 
corresponding unsynimetrical compounds, benzaurine, Doebner's violet and 
malachite-green. I find that the explanation is that the tautomerism 
/ 
has a lower value than the simple tautomerism CCC, the existence of two 
simultaneously available paths apparently making the orbit smaller and the 
periodic-time less. The value is about 96. It is also to be noted that 
the whole tautomeric chain in these dyes is no longer than before, viz. 
5 tautomerisms, not 8, because the orbit can only go througli two of the 
benzene-rings at a time, never through all three in succession. Consequently 
aurine is a loaded dioxybenzhydrol, parafuchsine is a loaded diaminobenz- 
hydrol, and crystal- violet is a loaded Michler-hydrol. The general formula 
being C^(C6H4X)3, my supposition is that the colour is due to two groups 
C6H4X united by the tautomerism 
;c - c 
