Chemistry and Physics. 249 



tional plan here adopted is approved, the book will be a good one 

 for younger students of chemistry. h. l. w. 



6. Experimental Electro- Chemistry, by N. Monroe Hopkins. 

 8vo, pp. 284. (D. Van Nostrand Co., 1905.) Price, $3.00 net.— 

 As the name indicates, this book deals more particularly with 

 experimental electro-chemistry. The theory of electrolytic dis- 

 sociation is presented with some experimental evidence to support 

 it. Detailed directions are given for a number of electrolytic 

 preparations. The action of primary and secondary cells is dis- 

 cussed and illustrated by experiments. An excellent bibliography 

 of the more important works on electro-chemistry is given at the 

 end. There are some rather surprising omissions. Thus, while 

 two chapters are devoted to the theory of electrolytic dissociation, 

 there is hardly a mention made of the electrical methods of meas- 

 uring dissociation. Instead, the method depending on the depres- 

 sion of the freezing point is described in some detail, though this 

 method is hardly to be classed under electro-chemistry. 



H. W. F. 



7. Radiation from Ordinary Materials. — Norman B. Camp- 

 bell sums up a. paper on this subject, containing the results of 

 work done in the Cavendish Laboratory, as follows : " If the 

 object of this paper has been attained, it has been proved beyond 

 doubt, that the emission of ionizing radiation is an inherent 

 property of all the metals investigated ; and I see no reason why 

 it should not be extended to all substances. It is not of course 

 necessary that this ray emission should be identified at once with 

 radio-activity — if that word be taken to mean a process of ray 

 emission accompanied by atomic change. But the constant 

 intensity of the rays and the probability that the greater propor- 

 tion of them are a rays, which is suggested by the investigation 

 of their charge and their penetration, afford considerable support 

 for that hypothesis ; while I know of no other process which 

 affords any analogy. But before the identity can be established 

 irrefutably further work is required, which I hope to be able to 

 supply in the future," — Phil. Mag., No. 62, 1906, pp. 206-226. 



J. T. 



8. Spark Potentials. — Various observers have compiled tables 

 of such values for the information of electrical engineers. M. 

 Toepler gives the following table as the result of recent investi- 

 gation. 



Sparking dis- 

 tance in cm. 5 10 15 20 25 30 35 40 45 



Kilovolt ob- 

 served 31-6 46-6 634 78-9 94-6 112-2 1254 139-1 153'8 



Kilovolt cal- 

 culated by 

 Walter ... 31 -6 471 62-7 78-2 93"8 109"3 124-9 140-4 156-0 



Kilovolt cal- 

 culated by 

 Toepler... 27-97 46-38 63-20 79-24 94-75 109-88 124-73 139-38 153-82 



—Ann. der Physik, No. 1, 1906, pp. 191-209. j. t. 



