58o 



NATURE 



[August 15, 1907 



should be inclined at the angle of friction to the 

 horizon instead of being horizontal. 



Suppose next that the inquiring reader wishes 

 to put the examples on the motion of pulleys of given 

 mass on pp. 202, 203 to a practical test. He goes to 

 a scientific instrument maker, and orders some ex- 

 pensive pulleys. However well he oils their bearings 

 to make them smooth, it is pretty certain they will 

 never move with the accelerations given by Prof. 

 Jeans's formulre. The tensions of a string may be 

 equal on both sides of a pulley so long as that pulley 

 remains at rest, but so soon as it begins to rotate 

 differences of tension will be set up, and no amount 

 of lubrication applied to the bearings will affect the 

 result. Of course, if the inertia of the pulley is 

 small, the tension differences will also be small, but 

 the masses of the pulleys are " given " in the ques- 

 tions, and the proper lesson to be learnt is that a 

 solution of the problems which does not take account 

 of rotational as well as translational inertia is in- 

 correct. 



There are several good features, however, which 

 well deserve mention. Among these are the treatment 

 of strings, including the early references to Hooke's 

 law, the example on p. 53, with its neat geometrical 

 solution, the example on p. 360, in which accelera- 

 tions in polar coordinates are deduced from La- 

 grange's equations, and finally the omission of all 

 references to poundals, slugs, and other abominations 

 of the same nature. It is a pity that some of the 

 examples involve the usual tedious and uninteresting 

 drudgery in the form of multiplication or division 

 by 2240 or 5280 or 1728 or 33,000, or another of the 

 same series of objectionable numbers. We do not 

 blame Prof. Jeans for following the common prac- 

 tice in this respect, as most of us find ourselves forced 

 to do the same, but surely the time has come w-hen 

 examples involving the metric system may figure more 

 freely than they do in treatises on theoretical 

 mechanics, especially when those treatises are particu- 

 larly adapted for students of physics. G. H. B. 



THEORETICAL ELECTROCHEMISTRY. 



The Electrolytic Dissociation Theory. By Prof. R. 

 Abegg ; translated by Dr. Carl L. von Ende. Pp. 

 ix+i8o. (New York: John Wiley and Sons; 

 London : Chapman and Hall, Ltd.) Price 55. 6d. 

 net. 



Electrochemistry. Part L, Theoretical Electrochem- 

 istry and its Physico-ch.mical Foundations. By 

 Dr. Heinrich Danneel ; translated by Dr. Edmund 

 S. Merriam. Pp. vii + iSi. (New York: John 

 Wiley and Sons; London : Chapman and Hall, Ltd.) 

 Price 5s. 6d. net. 



THE advent of the translation of these two little 

 books into English shows that the subject 

 of electrochemistry, or rather, we should say, 

 physical chemistry, with an electrochemical bias is 

 coming more and more to the front. But while we 

 have had of late a large number of books upon the 

 theoretical side of the subject, there is not very much 

 NO. 1972, \0L. 76J 



literature dealing with the practice of electrochemistrv 

 and its applications to industrial problems. 



Prof. Abegg's book is a translation of the author's 

 " Die Theorie der elektrolytischen Dissociation," 

 which appeared in 1903 in the " Sammlung chem- 

 ischer und chemisch-technischer Vortrjige." Prof. 

 Abegg starts off in an elementary manner, and ex- 

 plains the dissociation theory so that the beginner may 

 understand the subject. On several occasions he uses 

 the term osmotic pressure, but throughout the 

 book he does not explain what osmotic pressure is or 

 how it is measured. Although the commencement of 

 the book is quite simple, it is not long before Prof. 

 Abegg revels in mathematics, which, combined with 

 the slavish style of the translation, makes the reading 

 rather uninteresting. The section upon equilibria 

 among several electrolytes is very long, and includes 

 subsections upon hydrolysis, avidity or affinity of 

 acids and bases for each other. The style of the book 

 may perhaps be shown by the following passage : — 



" Since in the case of equal concentration the ionic 

 concentrations of pure (unmixed) acids are to each 

 other as the roots of their dissociation constants, we 

 may with Arrhenius also express this equation thus, 

 that both acids divide themselves between the base in 

 the same ratio as their degrees of dissociation would 

 be, if each were present alone in the volume con- 

 sidered.'' 



•A section is also devoted to " non-aqueous solu- 

 tions," and in it the author explains some of the 

 difificulties which occur when one tries to bring the 

 behaviour of solvent and solute into line with a similar 

 substance dissolved in water; for example, the com- 

 plications arising by the phenomena of the association 

 of the non-ionised portion of the electrolyte. The book 

 is a useful review of the ionic theory written entirely 

 with the view of supporting the theory. 



Dr. Danneel 's book, although it explains the ionic 

 theory in considerable detail, is an exposition of 

 general theoretical electrochemistry. The book begins 

 with an explanation of the terms work, current, and 

 voltage. The gas laws lead up to osmotic pressure, 

 which is fully and lucidly presented. The theory of 

 electrolytic dissociation and conductivity brings us up 

 to p. 114. The average student who is called upon to 

 study the ionic theory will obtain, we venture to think, 

 a better grip of the subject by a study of Danneel's 

 book than from that of Abegg. The latter book treats 

 the subject more fully, but Danneel's style is more in- 

 teresting, and he leaves none of the salient facts out. 

 Chapter v. treats of electromotive force and the 

 galvanic current, and chapter vi. of polarisation and 

 electrolysis. The last chapter, which is very short, 

 treats of the electron theory. W'e find it here stated 

 that " The electron acts chemically like an element. 

 It combines with other elements to form saturated com- 

 pounds, which are the ions "; thus 



CI + = C10 = C1'. 



It would have been of special interest had Dr. Danneel 

 enlarged upon this subject ; he has, however, just 

 given enough to make it suggestive. 



