308 REPORTS ON THE STATE OF SCIENCE, ETC. 



have a quiiionoid structure owing to their visible colour, but there is no 

 evidence whatever to support this conclusion. The extraordinary readiness with 

 which they pass with evolution of energy into their stable colourless phases 

 strongly supports their being metastable phases having the usually accepted 

 structure. Other examples of this phenomenon may be found in the existence 

 of many substances in two modifications, of supercooled liquids, etc., but as yet 

 the phase explanation of these lacks the corroborative evidence of absorption 

 spectra observations. 



Although these molecular phases have been discussed for compound mole- 

 cules, they also exist in the case of elementary molecules, and there is little 

 doubt that the phenomenon of allotropy is merely one of equilibria between 

 different phases of the same molecule. The allotropy of sulphur has been 

 examined from this point of view, the various allotropic modifications being 

 different equilibrium mixtures of the four phases SA, S-, S^, and S/i. Each 

 of these phases in solution in the proper solvent — namely, carbon bisulphide, 

 toluene, chloroform, and piperidine, respectively — exhibits its own absorption 

 band, and the central frequencies of these bands are all exact multiples of 

 the molecular frequency of sulphur in the infra-red. This explanation of 

 allotropy has also been given by Smits, whose molecular species are in reality 

 molecular phases. 



Two final examples may be given of this phenomenon, and the first is the 

 preparation of two kinds of ammonia which differ in the equilibrium between 

 the two phases present. These tvv'o types of this gas can be obtained by the 

 slow and explosive evaporation of the liquefied ammonia, and they differ very 

 remarkably in the amount of energy required to det ompose them into nitrogen 

 and hydrogen (Baly and Duncan, 'Trmis. Chcm. Soc, 121, 1U08 (1922)). The 

 gas oljtained by the sudden evaporation of the liquid contains more than the 

 normal proportion of the more condensed phase, and therefore requires more 

 energy to decompose it. 



The last example is found in the most interesting results obtained by Baker 

 (Trans. Chcm. ;Soc.,211, 56S (1922)) on completely drying a number of liquids. 

 He found that after drying them over phosphoric oxide for a number of years 

 the boiling-points of the liquids were very considerably raised. There is no 

 doubt that the normal phase equilibrium in these liquids at ordinary tempera- 

 tures is manitained by the traces of water present. On complete removal of 

 the water the phase equilibrium is shifted towards the side of the more con- 

 densed phase. In order to convert the dried liquid, therefore, into the normal 

 vapour, more energy will be required than with the moist liquid, and thus the 

 boiling-point will be raised. 



In concluding this section of the report, the phase theory may be applied 

 to one of the many interesting problems of the organic chemistry of to-day — • 

 namely, that of free radicles. It is known that compounds of the type of 

 hexaphenylethane, (C^H^)2C — C(pH.)^, dissociate into the free radicles, e.g. 

 triphenylmethyl, (0^.11. )jC, and considerable difficulty is found in explaining 

 why less energy is required to dissociate such a compound than is required 

 in the case of the parent substance, ethane, the bond between the two central 

 carbon atoms being the same in the two cases. The explanation, however, is 

 at once supplied by the phase hypothesis and supported by absorption spectra 

 observations. In the case of ethane the external force fields of the atoms 

 are well balanced, so that the molecular force-field condensation proceeds far 

 with the evolution of many molecular quanta and the formation of a phase of 

 small energy content. This is proved by the fact that the phase frequency of 

 ethane lies in the extreme ultra-violet. In order, therefore, to dissociate a 

 molecule of ethane into free methyl radicles the amount of energy required will 

 be very large indeed. When the hydrogen atoms of ethane are progressively 

 substituted by phenyl, the balance between the atomic force fields becomes more 

 and more disturbed, and in he.xaphenylethane this effect is so pronounced that 

 the molecular force-field condensation cannot proceed very far. A much smaller 

 number of molecular quanta are lost, and the frequency of the resulting phase 

 lies on the border of the visible region. A much smaller amount of energy 

 will thus be necessary to dissociate this compound, owing to the fact that it 

 exists in a phase of much higher energy content. The difference between the 

 two compounds, ethane and hexaphenylethane, as regards their dissociation 



