May 4, 1905] 



NATURE 



ject-matter appears to be quite a proper one, for at 

 the present time almost everyone is familiar witfi the 

 elementary properties of gear-wheels, clutches, the 

 mechanism of steam engines and the like, because 

 of their increasing use in everyday life, and more 

 especially of late, owing to their applications to self- 

 propelled vehicles. On the other hand their less 

 obvious, although not less important, properties are 

 possibly not so well understood ; thus, to take a single 

 instance, the conditions to be satisfied in order to 

 produce true rolling motion by gear wheels require 

 a knowledge of the properties of various curves, and 

 this latter subject may well be left to a later stage, as 

 is done in the present work, although it need not pre- 

 vent a study of machines containing gear wheels 

 when this knowledge is not absolutely necessary for 

 the purpose. The author has therefore described 

 many machines using higher pairing quite early in 

 the book, and has left the more detailed examination 

 of some of the elements for later chapters; this adds 

 very much to the general interest of the reader, while 

 its drawbacks are small. The work opens with an 

 introductory chapter in which the usual definitions 

 occur relating to machines, kinematic chains, lower 

 and higher pairs, and the like, and this is followed 

 by a chapter which is exceedingly interesting on simple 

 machines and machine tools. 



Chapters iii. and iv. deal chiefly with mechanisms i 

 of the quadric crank and double slider crank chain | 

 forms, all those possessing important geometrical 

 properties being grouped together. Naturally the 

 pantograph finds an important place here, and to 

 amplify this section there are descriptions of the 

 copying lathe and also a machine on the same prin- 

 ciple for drilling square and hexagon holes. In a 

 future edition it might be worth while to insert, in a 

 suitable place, an account of the epicyclic trains which 

 form an essential part of some machines for turning 

 nuts and bolts to a practically perfect square or 

 hexagon section. 



The next two chapters deal with velocity and 

 acceleration diagrams, and we are sure that all 

 students of mechanism will feel greatly indebted to 

 the author for the clear manner in which he has pre- 

 sented this part of the subject. The remainder of the 

 book deals with gear wheels, non-circular wheels and 

 cams, and these are discussed on the usual lines. 

 There is also a section devoted to gear-cutting 

 machinerv, which gives an interesting account of this 

 special branch of machine tool work. 



It is somewhat remarkable that no place is found 

 in the book for the consideration of so fundamental a 

 subject as the degrees of freedom possessed by a body 

 and the applications which follow from a recognition 

 of these principles in geometrical slides and clamps, 

 such as are described in Thomson and Tait's " Natural 

 Philosophy." Ignorance of these fundamental prin- 

 ciples has been one of the most fruitful causes of bad 

 design in mechanism. 



The illustrations are mainly line drawings, exceed- 

 ingly well adapted for descriptive purposes, and with 

 a few exceptions the photographs of machinery are 

 clear and distinct. A series of numerical examples at 

 the end of the book will be of much value to students. 

 NO. 1853, VOL. 72] 



The author has succeeded in writing a valuable 

 text-book on mechanism which will repay a careful 

 study by engineers and others who wish to obtain a 

 knowledge of something more than the elements of 

 this branch of science. E. G. C. 



PRACTICAL ELECTROCHEMISTRY. 

 Practical Methods of Electrochemistry. By F. Mollwo 

 Perkin. Pp. x + 322. (London : Longmans and 

 Co., 1905.) Price 6s. net. 



ELECTROCHEMICAL methods, both of analysis 

 and preparation, have in recent years under- 

 gone such rapid development, and have reached such 

 a degree of importance, that systematic instruction 

 in their employment has become an indispensable part 

 of the training of the modern student of chemistry. 

 This book, therefore, forms a welcome addition to 

 the ordinary laboratory manuals. 



After a general account of electrical magnitudes 

 and units, measuring instruments, and electrolytic 

 apparatus, the author gives practical instructions for 

 electrochemical analysis. The conditions for the 

 quantitative electrodeposition of the individual metals 

 are first discussed ; then follows a section on quanti- 

 tative oxidation and reduction at the electrodes, and, 

 finally, directions are given for the separation of 

 metals from mixed solutions of their salts. The last 

 and longest section of the book deals with preparative 

 electrochemistry. The primary subdivision of the sub- 

 ject is into the preparation of inorganic and of organic 

 compounds, the latter section being treated in three 

 chapters on organic electrolysis, reduction of organic 

 compounds, and oxidation of organic compounds re- 

 spectively. 



The practical instructions are on the whole 

 adequate and accurate, so that the student could 

 acquire with little assistance a sufficient acquaintance 

 with the working methods of electrochemistry. 

 Whilst the book is satisfactory in this, the most im- 

 portant, feature, it shows in other respects many 

 signs of hasty composition, which greatly detract from 

 its value. For e.xample, there are frequent evidences 

 of haste in the treatment of electrical units. In the 

 table on p. 9 the heading of the last column but 

 one is " electrochemical equivalent per coulomb in 

 mg. per sec"; the words "per sec." are not only 

 superfluous but misleading. On p. 29 we find 

 " I kilowatt= 101-93 kilogrammeters," and " i horse- 

 power is 75 kilogrammeters," where the words "per 

 second " should have been added in both cases. 

 Nothing is more detrimental to clear thinking on the 

 part of the student than slipshod statements of this 

 kind. Again, in the table of " useful data " on 

 p. 286 we find " I kilowatt=iooo watt-hours," and 

 " volt X amperes = watts." Such data are the reverse 

 of useful. A curious batch of mistakes is to be found 

 on pp. 231-232. It is stated on p. 231 that the electro- 

 lyte for the preparation of diethyl succinate is " acid 

 potassium or sodium malonate " instead of " ethyl 

 potassium or sodium malonate." On the same page 

 we twice find " diethyl adipic acid " instead of diethyl 

 adipatc, and on the succeeding pages a similar error 



