August i8, 192 i] 



NATURE 



m 



therefore required of the third edition of the 

 second volume of the series. The principal 

 additions that have been made deal with 

 the e.m.f. method of determining the trans- 

 port number of an ion, as employed by 

 Maclnnes and Parker, the work of Richards and 

 Daniells on thallium-amalgam cells and of 

 Tolman on centrifugal cells, American work on 

 ionic activity, experimental work in support of, 

 Donnan's theory of membrane-equilibrium, and 

 the work of McBain on colloidal electrolytes. 

 Much of this new material is described in the 

 words of the original investigators, as has already 

 "been done in earlier parts of the book. 



(2) The determination of hydrogen-ions has be- 

 come a very important section of physical 

 chemistry, especially in its application to bio- 

 logical problems. The fact that Dr. Clark's book 

 on this subject has been produced from the 

 Research Laboratories of the Dairy Division of 

 the U.S. Department of Agriculture is one indica- 

 tion of the practical apphcation of the various 

 methods of measurement which the author de- 

 scribes. These include the use of indicators, of 

 liydrogen and calomel electrodes, and a few sup- 

 plementary methods. The applications of these 

 methods are so numerous that it is almost impos- 

 sible to describe them adequately in any single 

 volume ; the chapter which deals with these appli- 

 cations has therefore been written in the form of 

 a classified bibliography, the detailed references 

 for which occupy 64 pages of the text. 



A noteworthy feature of the book is a chart show- 

 ing the colour of eight different indicators at nine 

 hydrogen-ion concentrations, covering in each case 

 the change from the alkaline to the acid colora- 

 tion. The frontispiece is a photograph of Prof. 

 Sorensen. The book is likely to prove of great 

 value either to the physical chemist or to the bio- 

 chemist who wishes to take up the very fascin- 

 ating and fertile branch of study with which it 



deals. 



(3) The appearance of the second edition of 

 Prof. Edwards's " Physico-Chemical Properties of 

 Steel " affords an opportunity of directing the 

 attention of the readers of Nature to a valuable 

 book which has not been reviewed previously in 

 these columns. A book with this title may be 

 criticised either as a contribution to metallurgy or 

 as an application of physical chemistry to a group 

 of technical problems. As the author is a metal- 

 lurgist, the reader will expect to find the technical 

 side of the work well developed, and he will not 

 be disappointed. 



The physical chemistry is more open to criti- 

 cism : thus a paragraph on " allotropy " (a 

 generic term covering at least three distinct 

 NO. 2703, VOL. 107] 



phenomena) is not a satisfactory substitute for a 

 clear description of the phenomena of isomorphism 

 and polymorphism; the idea of "crystal bricks " 

 is so far obsolete that it should surely be replaced 

 by some account of the theory of space-lattices ; it 

 is impossible, even on the authority of Ewing, to 

 accept the suggestion that rotating the " bricks " 

 through an angle of 180° could possibly give rise 

 to twinning — perhaps an angle of 90° was meant, 



A few verbal errors have escaped correction in 

 this edition, and the lettering of some of the dia- 

 grams has been reproduced by a process which 

 leaves much to be desired in the matter of legi- 

 bility. The micrographs, on the other hand, are 

 a most attractive feature of the book, and none of 

 them are more effective than those which the 

 author has produced to show the formation of 

 twinned crystals and of slip-bands as a result of 

 mechanical strain in metals. 



For the physical chemist Prof. Edwards has 

 provided a mine of valuable information, bearing 

 on the application to metallurgy of his branch of 

 chemistry. Even the student is now generally 

 familiar with the iron-carbon diagram and the 

 general relationship of this diagram to the pro- 

 perties of the carbon-steels ; but it is equally true 

 that the parts played by sulphur and phosphorus 

 are not generally known, even to the teacher of 

 physical chemistry. It is a great convenience to 

 have the available information put together in a 

 concise form by one who is thoroughly familiar 

 with the practical and not always harmful effects 

 of these important impurities. The effects pro- 

 duced by manganese, chromium, tungsten, alu- 

 minium, silicon, and vanadium are also described, 

 as well as the properties of special steels, such as 

 high-speed tool steels and a number of ternary 

 steels. The two new chapters in the second 

 edition deal with the more important methods of 

 making hardness-tests, and the influence of con- 

 stitution on electrical resistivity. 



Whilst the reviewer is not competent to assess 

 the value of this book as a contribution to metal- 

 lurgy, he can assert confidently that no physical 

 chemist who has to teach students of engineering 

 or metallurgy can afford to be without it, and that 

 the information which it gives will broaden the 

 outlook of any student of physical chemistry who 

 may read it. 



(4) Prof. Moldenhauer's book on the re- 

 actions of free nitrogen does not profess to 

 deal with physical chemistry, and an apology is 

 perhaps needed for including it in this category ; 

 but the nature of the subject is such that the main 

 chapters of the book are necessarily physico- 

 chemical in character, dealing as they do with 



