ON DYNAMIC ISOMERISM. 199 
for the different isomerides, though large accidental discrepancies may 
occur when isomeric change depends on a small amount of a third 
substance. A fair agreement between the two periods was observed in 
solutions in benzene of normal and pseudo z-bromonitrocamphor ! but 
Forster’s curves for the two a-benzoylcamphors show a period twice as 
great for the ketonic as for the enolic form. 
7. Catalytic Agents alter the velocity of Isomeric Change but do not 
disturb the Equilibriwm.—Schiff? supposed that in the case of ethyl 
aceto-acetate 
CH,.CO.CH,.CO.OEt 2 CH;.C(OH) : CH.CO.OEt 
the material was converted by a trace of sodium ethoxide wholly into the 
enolic, and by a trace of piperidine wholly into the ketonic, form. This 
is impossible on theoretical grounds and has been disproved experi- 
mentally in this and in other cases.* It therefore follows that catalytic 
agents accelerate both isomeric changes in the same ratio. 
8. The Equilibrium may be affected by the Solvent, Concentration and 
Temperature.—The direct effect of these is probably small, but if there is 
a tendency for one or both of the isomerides to polymerise, as in the case 
of the nitroso- and many hydroxylic compounds, or to combine with the 
solvent, as in the case of normal nitrocamphor dissolved in benzene, or to 
combine with one another, as in the case of thiourea and ammonium 
thiocyanate 4 or to become ionised, as in aqueous solutions of the cyanates 
and pseudonitro- compounds, very marked effects may be indirectly 
produced. Thus Wislicenus has shown ® that associating solvents and 
high concentrations favour the formation of the (dimolecular) enolic form 
of ethylic phenylformylacetate 
CHO.CHPh.CO,Et @ HO.CH : CPh.CO,Et. 
In the contrary direction, Perkin has shown® that high temperatures 
increase the proportion of the ketonic form of the diketones, probably by 
dissociating the dimolecular enolic forms. 
The great increase in stability of ammonium cyanate in dilute aqueous 
solution may be attributed to the large proportion of the salt which is 
then in an ionised condition and only indirectly available for isomeric 
change— 
+ — 
CO(NH,), 2 NH,.0.CN 2 NH, | OCN. 
Thus Walker and Hambly’ have obtained evidence that at the dilution of 
N/2000 ammonium cyanate and urea would be equally stable, and would 
be present in equal proportions in the mixture. On somewhat similar 
lines Hantzsch and Kinchenberger have contended ® that nitroform in 
anhydrous solvents exists almost exclusively in the normal modification, 
but that in aqueous solutions it is mainly in the ionised pseudo- modifica- 
tion, psewdo-nitroform being one of the strongest known acids : 
- + 
CH(NO,), 2 (NO,),CH : NO,H 2 (NO,)CH : NO, | H. 
! Loe. cit. 2 Ber, 1898, 31, 601. 
$ See Schaum, Ber. 1898, 31, 1964; and Lowry, Trans. 1899, 75, 223. 
4 Reynolds and Werner, loc. cit. 5 Ann. 1896, 291, 182. 
® Trans. 1892, 61, 801. 7 Loe. cit. 
8 Ber, 1899, 32, 628. 
