•212 
Tranmdions of the lloyrd Sorieiy of Soufli Africa. 
NH, and tlierefore slioiild have X about 365, whereas it is really about 420. 
Two other partial anomalies are fuchsimonium chloride and its dimethyl- 
derivative, which have very broad absor])tion bands at W 430 and 460 
respectively in alcohol. The formula 
Ph.,C =<^ ^=NH,C1 
corresponds to the tautomerism 
^ "^C = C 
combined with the C,.H^NH^ ring and two phenyl loads. This would be 96 
+ 223 + 32 = 351 ; similarly the dimethyl derivative would work out at 
379, both of which calculations are about 80 units too low. Now colour 
and broad bands similar to these are obtainable from malachite-green and 
crystal-violet by adding an excess of acid, the observed wave-lengths being 
about X 438 and X417 respectively. It is evident that these five cases cannot 
be explained oil an exact quantitative basis, and I suggest that in all of them 
the tautomerism penetrates into one of the benzene-rings in a highly per- 
turbed orbit, thus accounting for both the breadth of the band and its 
abnormally high position ; the orbit w^ould thus be of the following type in 
which the irrei>'ular orbit varies in value between 80 and 100. 
Fnchsonedimethylimoniiim salt X 460 in alcohol. 
Having now shown the weaker points of the theory, it may be well to 
show how it explains the colours of tlie phthaleins or other well-known 
substances. Since the CO.iH group of the phthaleins is outside the tauto- 
merism it makes scarcely any difference ; observation shows that any 
substituted plienolphthalein has a spectrum which is only one to two units 
different from that of the corresponding benzaurine. Thus the central 
COoH 
group may be taken to be of value -i- 18 when phenyl is -f 16. Again, it is 
shown on p. 207 that an ortho-substituent puts the value up by 7 and a 
meta by 15. Hence the ring 
— <z>- 
lias a value of 219 -t- 7 = 226, the ring 
— <z>- 
