106 Prof. H. E. Armstrong. On Chemical Change, [Mar. 13, 



will be possible to correlate the production of visible colour with that 

 of a luminous spectrum, and to regard both as originating in the same 

 intramolecular mechanism. — Note,- added May 2.] 



The argument may be carried a stage further and applied to phos- 

 phorescent phenomena generally. It appears possible to regard all 

 these as the outcome of oscillatory changes in molecular structure — 

 and the slow decay of the effect which is observed in many cases may 

 be compared with the slow discharge of a condenser — the charging of 

 which be it noted may be regarded as but a process of molecular 

 deformation of the dielectric. 



In a case like that of radium, it would seem that energy of low 

 period suffices to bring about the change the reversal of which subse- 

 quently gives rise to the luminous effect and radio-activity. The chemist 

 is tempted to contrast the behaviour of radium with that of a substance 

 undergoing change into an isodynamic form — such as nitro-camphor, 



CH.N0 2 



for example. Nitro-camphor C 8 H u < i dissolves readily in 



alkalies, but its salts are derived from a pseudonitro-camphor, the group 

 CH . N0 2 undergoing alteration into the group C (NO . OH). When 

 liberated from its salts, the pseudo-form at once, in great part, reverts 

 to the normal form ; on the other hand, when solid nitro-camphor, 

 which apparently consists almost entirely of the normal form, is 

 dissolved in a liquid, it in part gradually undergoes conversion into the 

 pseudo-form. A point of equilibrium is eventually reached when from 

 7 to 10 per cent, of the pseudo-form is present.* The change proceeds 

 at different rates in different solvents, and is undoubtedly conditioned 

 by some catalyst : in other words, either form of the pure substance 

 would be stable. It will be apparent that the change is one which 

 does not affect the molecule as a whole, but merely an isolated region 

 in it. If the energy set free in the formation of the dominant form 

 were of sufficiently high period, nitro-camphor might appear luminous 

 and even be radio-active. The argument is of interest, as it serves to 

 suggest that radio-activity may not be the isolated phenomenon we at 

 present suppose but a concomitant of some chemical changes. 



[From this point of view, it appeared to be desirable to examine 

 substances such as saccharin (orthobenzoic sulphinide) and cane- 

 sugar, which glow in a very remarkable manner when broken up. 

 Mr. E. W. Lewis has kindly made a number of experiments for me, 

 but without obtaining positive results : although an intense photo- 

 graphic impression of the flash is easily obtained by merely crushing 

 crystals of saccharin or sugar on a glass plate held above a sensitive 

 film, crystals placed on a film are without effect, even when left in 

 contact with it during several days. It will, however, be desirable to 



* Comp. Lowry, ' Chem. Soc. Trans.,' 1898, p. 966. 



