Mr. H. Jackson on Phosphorescence. 405 



complexity, the red being related to more complex groups, 

 the orange to less, and so on. It seemed not unlikely that it 

 might be possible by preparing lime from a great many 

 calcium salts to obtain separate specimens which might pre- 

 serve in the solid state some relation in their own molecular 

 complexity to that of the salts from which they were obtained, 

 or the conditions of decomposition of the different calcium 

 salts might impress upon the residual limes different 

 characters of molecular structure. The preparation of about 

 350 specimens of lime showed that it was quite possible to 

 get specimens some of which phosphoresced red, some orange 

 red, some orange, others green, and some blue. Examination 

 of their phosphorescent lights with the spectroscope showed, 

 as referred to before, that the maxima of brilliancy in their 

 spectra were grouped about the bands and lines of the usual 

 spectrum of calcium oxide. The details of the preparation 

 of these specimens of lime are too elaborate to enter 

 into here, nor is it possible to do more than just to refer 

 to their varying densities and different rates of hydration. 

 Out of the number of specimens tried the most satisfac- 

 tory were analysed to make sure that it was really lime 

 and only lime which was being dealt with in each case. 

 In general terms it may be said that the most compli- 

 cated organic salts of calcium yielded the best attempts at 

 lime giving blue phosphorescence, simpler bodies gave green, 

 while the best orange was obtained from Iceland-spar and 

 the red from specially prepared calcium carbonate. That 

 lime yielding a blue colour was obtained from highly com- 

 plicated organic salts does not contradict the former sugges- 

 tion that perhaps it is really of simpler molecular structure 

 than the others. Chemists are familiar with the conception 

 that the complexity in structure arising from the massing 

 of many molecules together in groups is probably often 

 greater in bodies of apparently simple chemical composition 

 than in those of a much more highly complicated nature. 



The colours seen in the specimens of lime shown are not 

 pure. In each one the other colours are present ; thus the 

 orange contains also the red, green, and blue, only these are 

 masked by the greater proportion of the one colour. Com- 

 pare, for example, the light obtained from a vacuum-tube 

 containing the gas helium. In this case the colour is yellow, 

 although the spectrum contains beautiful red, green, and blue 

 lines. If the different colours are related to varying mole- 

 cular complexity in the substances, then it might be said that 

 the lime showing a green light contains a large proportion of 

 groupings of such a nature as to be capable of oscillating in a 



