PROGRESS IN PHYSICAL CHEMISTRY. 313 



ions exist in solutions of electrolytes the solvent will be 

 compressed in the field produced by the ionic charges. 

 The authors develop the theory of the subject, and recall 

 the fact that as dilution proceeds the calculated molecular 

 volume of a salt becomes less and less, and exhibits ap- 

 parently the increased contraction of the solvent clue to the 

 increased ionisation. Several cases are quoted to show 

 that the electrostriction thus produced by the dissociation 

 of one gram-molecule of salt into two monovalent ions is 

 almost the same, and varies between 8 and 11 c.c. 



Photochemistry. — Roloff (182) has studied the effect of 

 light on the interaction of mercuric chloride and ammonium 

 oxalate. Substances which increase the dissociation in- 

 crease the amount of mercurous chloride produced. He 

 concludes that only dissociated molecules take part in the 

 reaction which is carried on by Hg and C 2 4 ions. In the 

 case of the interaction of bromine and oxalic acid in the 

 light and in the dark he finds that the ratio of the velocities 

 increases rapidly with the time, and on the addition of 

 potassium bromide. In the potassium bromide solution 

 KBr 3 is supposed to exist, and the action of light is held to 

 increase the activity of the ions and the Br 3 group. 



An attempt to explain the development of the silver 

 bromide gelatine image of a photographic plate in terms of 

 the intensity of reducing agents as found by observations 

 on E.M.F., and by the application of the law of mass 

 action, has been made by Bredig (183). Dewar (184) 

 finds that at the boiling-point of liquid air photographic 

 action is reduced by 80 per cent. 



Lemoine considers that of the total light only 1/1 0,000th 

 is used in chemical work in the reaction between ferric 

 chloride and water (185). 



An electrode consisting of a silver plate coated with 

 silver bromide, which is sensitive to light, and which mio-ht 

 probably serve therefore as an actinometer, has been de- 

 scribed by Luggin (186). When paired with a silver plate 

 in a solution of potassium bromide the results are, however, 

 not very constant. 



