108 SCIENCE PROGRESS 



advanced by Baly on the subject. Baly's theory, in part at 

 least, associates the delicate changes of colour experienced by 

 many organic substances when the nature or concentration of 

 the solvent or some other variant is slightly altered, with a 

 process of opening up of the solute, in the sense that the chem- 

 ical forces within the molecule as a whole are no longer so 

 strong as originally in some particular horizon, which horizon 

 depends on the nature of the variant impressed. The change 

 is not one which affects what we might call the stereotyped 

 configuration of the molecule or system, but is one in which 

 a reactivity of some definite character, hitherto more or less 

 latent, is developed. On these lines it is possible reasonably to 

 explain many facts in organic reactivity which have been long 

 looked upon as empyrical results. Whilst Baly's theory has 

 been developed mainly in connection with organic chemistry, 

 it is nevertheless equally applicable to inorganic chemistry. 

 Inorganic chemistry, however, presents fewer examples of the 

 type met with in organic chemistry, possibly because the 

 opened-up phases have such temporary existence, or possibly 

 because these phases are evidenced by absorption spectrum 

 changes in an inaccessible region. The recent observations of 

 Goldstein on the production of colour in solid salts containing 

 infinitesimal impurities by bombardment with cathode rays, 

 are susceptible of explanation on the lines of this theory, and 

 the same is the case with the observations of Weimarn on 

 coloured solutions of sulphur to which we have referred. Wei- 

 marn finds that sulphur dissolves with an indigo or blue 

 coloration in water, ethyl, propyl, isobutyl, and amyl alcohols, 

 acetone, glycerol, and ethylene glycol if these solvents are 

 rendered alkaline. In a few cases the trace of alkalinity de- 

 rived from the glass of the containing vessel is sufficient to 

 induce the blue colour. In neutral or acid solutions, however, 

 no coloration is developed — the explanation of which, on the 

 lines of the above theory, is that the sulphur molecule complex 

 possesses an acidic nature, and is consequently opened up and 

 made reactive by basic or basified solvents. When the solvents 

 possess a neutral character per se, or are acidified, the tendency 

 will be for the sulphur molecule to remain unaffected or become 

 closed, and consequently colour will be absent. Further, 

 Weimarn has noted that any solution of a polysulphide becomes 

 blue on heating, provided the solvent is not acid in character, 



