'September 3. 1903] 



""^kT^RE 



431 



Comparable with these are the two igodynamic forms of 

 ■K and /3-bromonitrocamphor, for ^Xai?i^le : — • 



/CH.NO2 

 QH^Br/ I - 



Normal neutral form. 



.C:NO„H 



C8H,3Br< 



Pseudo-acid form. 



In the solid state, both . forms of ir-bromonitrocamphor 

 are stable; when either form is dissolved in a liquid, 

 isomeric change sets in ; sooner or later, it may be only in 

 the course of a few hours or even days, a state of equilibrium 

 is established, about b per cent, of the material being pre- 

 sent in the pseudo form, and 94 per cent, in the normal 

 form. The change, however, does not occur spontaneously, 

 but is undoubtedly dependent on the presence of a catalyst, 

 a« equilibrium is established with great rapidity if a trace 

 of alkali be added ; acids have only a slight, although 

 definite, accelerating effect. In the case of 3-bromonitro- 

 camphor, solutions in benzene of the neutral as well as 

 of the acid form which have been kept during several 

 days without undergoing change, when transferred to 

 another vessel, have rapidly passed to a condition of 

 equilibrium — doubtless because this vessel had been less 

 successfully cleansed than that first used. It can, therefore, 

 scarcely be doubted that the change occurs within a com- 

 plex system — one which, it is only reasonable to suppose, 

 constitutes an electrolytic circuit. The process is reversed 

 when crystallisation sets in ; if the evaporation of the 

 solvent, take place sufficiently slowly, the whole of the 

 material is converted into and crystallises out in the less 

 soluble form ; if, however, evaporation take place rapidly, 

 the isomeric change may lag behind the crystallisation arid 

 both forms "may separate. In the case of nitrocamphor, the 

 normal form is the one that separates from the solution ; 

 but in the case of ir- and /3-bromonitrocamphor, although 

 the pseudo. form is the minor constituent .in the solution, 

 being much less soluble thah the isomeride, it is. one to 

 separate on crystallisation. ■ • ' ' 



The passage of the one form into the other in the case 

 of saccharin, for e.xample, may be pictured as involving the 

 as are represented in the 



occurrence of changes such 

 equation : — 



■ ±NaOH 



CeH4< 





/OH ±NaOH 

 ^ „ / ? ^ONa 



-^- 



-^ 



CfiH, 



xF-9.^^ 



i^*\ 



SO2- 



Supposing the stable form of loWer potential to crystallise' 

 out, the crystals, in almost every case, would contain a 

 minute and variable amount of the isodynamic form en- 

 .tangled, as it were, in the^mass. In the solid^ reversion to 

 the stable form would take place very slowly. Presumably, 

 however, sudden ' crushing of the crystals would afford' 

 opportunity for the change to take place and for the sudden 

 iiberation of energy — hence the momentary flash. • 



It is not, at present, necessary to assume that the pheno- 

 mena are limited to cases of isomeric change ; obviously, 

 changes such as those considered may be regarded broadly 

 as dissociative or reversible changes;' and from this point 

 of view, it is sufficient to regard the phenomena as the out- 

 come of a lo^ of potential consequent on the passage from 

 an unstable to a stable system. .1 . 



From the point of view here advocated, -it would be im- 

 possible to, construct a . condenser from a' />«re dielectric ; 

 and if the dielectric of a charged condenser were suddenly 

 smashed under suitable conditions, it might, exhibif/the 

 phenomenon of triboluminosity and perhaps, radio-activitvi 



Fluorescence. — It was originally suggested by one of the 

 authors, in. discussing the origin of Visible colour, that 

 fluorescence- is the ".beginning of colour." Subsequently, 

 Dr. J. T. Hewitt, in a. paper on the relation between con- 

 .stitution and fluorescence, published early. in 1900, took the 

 important step of associating the appearance of fluorescence 

 not with the mere occurrence of the quinonoid type of strjJi- 

 ;ture, but with the continued </cTTc/o/)m<?nr of" such* a "struc- 

 ture—in other words, he has regarded it as the outcome of 

 NO. 1766, VOL. 68] 



oscillatory changes in the course of which a non-quinonoid 

 compound undergoes conversion into the isodynamic 

 quinonoid compound. 



According to Hewitt, " all the molecules will be under- 

 going tautomeric change continuously and frequently, and 

 energy absorbed when the molecules have one configuration 

 will be, to an appreciable extent, emitted when they corre- 

 spond to the other configuration. It is practically certain 

 that the vibration frequency of fluorescein is different in the 

 two states, and hence every opportunity is offered for energy 

 of a rapid vibration frequency to be largely transformed into 

 energy of greater wave-length." 



Hewitt obviously does not regard fluorescence as a " flash 

 phenomenon," but as a form of colour, as it were. 



While agreeing with Hewitt that the origin of the effect 

 is to be sought in the occurrence of reversible changes*in- 

 volving the production of dynamic isomerides, the authors 

 think that fluorescence is to be regarded as something apart 

 from colour, which, more often than not, is superposed 

 upon colour. The character of the colour effect in fluores- 

 cence is quite distinctive ; it is not only remarkable on 

 account of its intensity, but there is in it an indefinable 

 qualitative difference which seems to separate it from 

 ordinary colour. If regarded as a "flash phenomenon" 

 this difficulty disappears. 



Hewitt appears to regard fluorescence as the outcome of 

 mere intramolecular wobble. To the authors it seems likely 

 that the change is conditioned by a catalyst, and that it 

 occurs within a complex electrolytic circuit. 



Phosphorescence. — The phenomena of^ phosphorescence 

 need to be considered with reference both to cases in which 

 the manifestation attends oxidative or other kinds of 

 chemical change (the glow of phosphorus, the glow-worm, 

 phosphorescent bacteria) and to those in which it is induced 

 by exposure to light (luminous sulphides). The former 

 might well almost be regarded as cases of fluorescence, as 

 a continual supply of energy is derived from the continued 

 occurrence of a chemical change involving loss of energy. • 

 With regard to the latter, it would seem that it is not a 

 property of pure substances. 



. The phosphorescent medium may. be pictured as a com- 

 plex system capable of undergoing " electrolytic " deform- 

 ation under the influence of light of high refrangibility ; as 

 the changes thus induced are reversed, the energy stored 

 up during insolation becomes liberated, and the persistence 

 of the effect is but a consequence of the fact that the change 

 takes place under restraint in a viscous medium. 



Dewar's remarkable observations on phosphorescence at 

 low temperatures clearly foreshadow the conclusion that the 

 property is to be correlated with structure. 



KaJio-.ictivity. — Pursuing the argument a stage further, 

 it appears to the authors justifiable to regard the activity 

 of radium tentatively as but an exaggerated form of 

 fluorescence in which radiations unnoticed by substances 

 generally — capable of penetrating substances generally — 

 become absorbed and rendered obvious. Such an explan- 

 ation, from the chemist's point of view, is at least as 

 •rational as one which assumes that nature has endowed 

 radium alone of all the elements with incurable suicidal 

 monomania. 



■ There seems to be no good reason for assurning that in 

 fluorescent and other ordinary substances we possess 

 screens capable of arresting rays of every conceivable kind ; 

 it may well be that our knowledge of solar, radiations is 

 not yet complete. " 



• With regard to "thorium and thorium X/' the facts, 

 as stated by Rutherford and Soddy, do not seem to be in- 

 compatible with the view that these are but isodynamic 

 forms of thorium or their equivalent, their behaviour being 

 very similar to that of the isodynamic forms of nitro- 

 camphor. In any case, it appears desirable to approach 

 the problem from this point of view, and to investigate 

 the phenomena far more thoroughly on the chemical side. 



Whatever the ultimate value of the considerations 

 advanced in the note, they at least serve to show that much 

 may be learnt by further study of the extent to which 

 luminous phenomena generally ..!are, to be correlated with 

 structure and structural changes. • -• 



July 21.—" On the Oxidising, Action- orthej Rays- iirom 

 Radium Bromide as shown bv the Pecompp^ition i)f Iodo- 

 form." By W. B. Hardi[,'^.R.S/,''Gaius.eoHe^e, Cam- 



