L SCIENCE PROGRESS. 



the concentration of the Hif ions in the solution. The generaUty of 

 such an objection is not affected by the fact that, in the case considered 

 the concentration of the mercury ions would be excessively small. The 

 remarks on the Influence of Negative Io)is {e.g., p. 227) seem open to 

 a similar objection. 



In the account of the capillary electrometer, the part played by 

 the acid is not made sufficiently clear. "Chemical Cells" are treated 

 as in Ostwald's Lehrhuch, and values for the "Heats of lonisation " 

 of different elements are tabulated. The source of the energy trans- 

 formed in the cell (apart from any heat which may be absorbed from 

 the environment) is thus made to depend upon the variation of energy 

 when an element changes into the ionic state. No suggestion as 

 to the nature of the variation is made; but a paper by J. J. Thomson 

 on " The Relation between the Atom and the Charge of Electricity 

 Carried by It" is of interest in this connection. 



The chapter on polarisation is the outcome of Le Blanc's own re- 

 searches. These are of great interest and form a most important contri- 

 bution to our knowledge of electrolysis generally. 



In connection with the theory of gas cells, an experimental determi- 

 nation of the temperature coefficient at different pressures {of., p. 254) 

 would be very useful. The peculiar position occupied, on Le Blanc's 

 view, (i) by hydrogen amongst kation-producing substances and (2) by 

 oxygen amongst anion-producing substances is worthy of notice. The 

 question of the capacity of the "double layer" at the electrode surface 

 is not considered by Le Blanc. In this respect his work is incomplete 

 for the question is one which is intimately connected with the theory of 

 electrolysis. A considerable amount of experimental information con- 

 cerning this has been published and it would seem that the views 

 developed in Le Blanc's book can be successfully extended to the 

 elucidation of some of the results. 



Finally, since many of the discrepancies which become evident 

 when the phenomena are examined in detail are still unaccounted for, 

 the physical basis of the book cannot yet be said to be perfectly secure. 

 It may however be reasonably held that the " most important term " 

 in the explanation of the phenomena has been discovered. The fruitful- 

 ness and utility of the " working hypothesis " can scarcely be questioned. 

 The views developed connect and arrange many of the facts of 

 electrolysis in a very remarkable manner and this is of the utmost 

 importance, for "of all electrical phenomena electrolysis appears the 

 most likely to furnish us with a real insight into the true nature of the 

 electric current". 



It should be added that the translation has been very well done, 

 the number of misprints and minor inaccuracies being unusually small. 



