Siipplcmcnt to "' N^ature" May 3, 1906 



his account of the later writcis, and enables us to 

 realise many circumstances \vhich coloured their 

 scientific work. 



It is interesting to learn that the majority of the 

 more notable of those who have created the science 

 of geology have been men engaged in other pursuits 

 who have devoted their leisure to scientific research. 

 Until lately there was no training in natural science 

 such as can now be obtained at our universities and 

 elsewhere. The nearest approach to it was the in- 

 struction given in the medical schools, and many of 

 the best geologists have been medical men. None 

 could, then, have been called professional geologists in 

 the sense of having been trained speciallv for geological 

 >tudy, and but few in the sense of having made it their 

 life's work and received pay for it, such as Sedg- 

 wick, who, having been a resident fellow of great 

 distinction in both classics and mathematics, was 

 appointed professor of geology, or Murchison, who, 

 having been a soldier, was made director of the Geo- 

 logical Survey. 



The author has recast and added to the biographical 

 sketches of the great leaders of geology as drawn in 

 his first edition, and has made a good book yet 

 better. It is a work which should be in the hands of 

 all students of geology, while the general reader can- 

 not fail to be interested in this chapter in the history 

 of discovery told in such charming, simple language. 



ELECTROCHEMISTRY . 

 Experimental Electrochemislrv. Bv N. Munroe 

 Hopkins, Ph.D. Pp. xiv + 284. (London: Archi- 

 bald Constable and Co., Ltd., 1905.) Price 12.S. 

 net. 

 'T'HE author's desire is, as he states in the preface, 

 to produce a book which will prove useful both 

 in the laboratory and in the lecture theatre, or, as he 

 probably means, for home study. The book com- 

 mences with a brief historical review of the subject, 

 and the student is intended to carry out some of the 

 classical experiments upon which the foundations of 

 this essentially experimental branch of chemistry 

 and physics have been built up. For example, he 

 is instructed how to repeat Sir Humphrv Davy's 

 work on the isolation of the alkali metres. A portion 

 of this chapter is also devoted to instructions how to 

 manipulate the electrical supply by cutting down the 

 current from the lighting mains with a lamp resist- 

 ance, or to alter the voltage by means of a small 

 motor generator. The author then comes to the sub- 

 ject of electrolytic dissociation. Dr. Hopkins is no 

 half-hearted supporter of the ionic theory; it is 

 evidently his sheet anchor, by which all other theories 

 must be tested, and if thev do not conform then there 

 is evidently something lacking in these theories. It 

 must be admitted that the author makes out a very 

 strong case for the theory of electrolytic dissociation, 

 and he gives experiment after experiment to prove 

 his case. Chapter ii. deals with osmotic pressure and 

 how to carry out the determinations ; a complicated 

 apparatus is described for experimentallv proving the 

 principle of Soret. In chapter iii. boiling- and 

 NO. 1905, VOL. 74] 



freezing-point methods are dealt with, and experi- 

 ments are described to show that chemical action will 

 not take place except in the presence of moisture. 



The next chapter treats of experiments in electro- 

 lytic induction. Some of these experiments are of 

 an extremely interesting character, although whether 

 opponents of the ionic theory would be prepared to 

 admit that they are valid proofs of the theorv is open 

 to doubt. Starting with the well known fact that a 

 negatively charged conductor will induce an opposite 

 charge in the end of a rod brought into its neigh- 

 bourhood, he describes experiments to show that the 

 same holds good in the case of an electrolyte, and 

 then argues that, as electricity can only pass through 

 a liquid by means of ions, therefore the induced 

 charge is caused by ionic movement. In the experi- 

 ment of Ostwald and Nernst, where the actual liber- 

 ation of hydrogen by an induced charge is made 

 visible to the naked eye, the proof seems complete. 

 The author, however, gives other verv interesting 

 cases where the induced charge is shown bv means 

 of a delicate mirror galvanometer, and in which no 

 chemical change is obvious, any more than it is 

 obvious in the case of a solid conductor. Some of the 

 most novel experiments in this direction described by 

 the author are those in which he shows that a magnet- 

 induces a current of electricity in an electrolyte, the 

 magnet being placed in the centre of a glass coil 

 containing the electrolyte. 



The chapter on the velocity of electrolytic con- 

 duction is interesting, and the question of the 

 absolute velocity of the ions is very fully dealt with. 

 Here again the author shows his ingenuity by the 

 number of novel experiments which he describes, and 

 bv his modification of the experiments of other 

 workers. A large number of experiments are de- 

 scribed to illustrate Faraday's laws, both in connec- 

 tion with dissolved and fused electrolytes. Dr. 

 Hopkins also describes an experiment to illustrate 

 the mechanical transfer of matter through solid glass. 

 .\ piece of glass rod is taken with platinum wires 

 fused into either end, the wires being about i cm. 

 apart in the centre. The two wires are connected in 

 scries with a milliammeter and with the electric 

 lighting circuit. No current, of course, passes, but 

 on heating with a Bunsen burner until the glass 

 commences to soften a deflection is noticed on the 

 ammeter. With the softening of the glass, there- 

 fore, the ions are free to travel, at any rate ; the glass 

 is no longer an insulator. 



The portion of the book dealing with electrolytic 

 analysis is very short, and will be useful more as a 

 suggestion as to what can be done than as a guide 

 for analytical purposes. To a certain extent the same 

 remarks apply to the electrolytic preparations which 

 are given. The part devoted to furnace work, that 

 is, laboratory furnace work, is pretty full. A good 

 deal of space is given to the isolation of aluminium 

 and also of sodium. The section devoted to calcium 

 should be brought up to date. 



An interesting account is given of the production 

 of nitric acid from the atmosphere, with historical 

 notes, and this chapter fails in one thing only — no 



