REVIEWS 331 



is really a separate branch of the science or whether it is not, in fact, simply 

 the third and last stage in the development of inorganic chemistry which 

 completes and rounds off the work of the earlier descriptive and classificatory 

 phases ? 



At all events the author has made full use of such modem developments 

 as equiUbrium diagrams and the like, which serve to make clear many 

 matters otherwise difficult for the student to grasp. 



The initial chapters are adapted from the author's Historical Introduction 

 to Chemistry, from which it will be gathered that the historical method of 

 approach has not been neglected. A useful device for students is the 

 inclusion at the end of each of the earUer chapters of a " Summary and 

 Supplement " which %vill aid materially in revision of work. 



Prof. LowTy has been fortunate in securing the collaboration of various 

 fellow-chemists, of whom Dr. A. S. Russell (Radio-activity), Dr. F. W. 

 Aston (Isotopes), Prof. W. Turner (Glass), and Mr. F. Renmck (Photo- 

 graphy), may be mentioned as contributing sections dealing with their 

 special subjects. 



The only comment that might reasonably be made by an " Advocatus 

 Diaboli " is whether too much is not attempted in writing a book which 

 begins with the very rudiments and carries on right into the most advanced 

 portions of the subject ? Either the beginner will be confused by the 

 apparent complexity of his subject or, alternatively, a large portion of the 

 book will remain unread by the senior man. This, however, is by the way. 



It would be invidious to compare the book with certain other excellent 

 textbooks of inorganic chemistry wliich have recently appeared, but quite 

 certainly Prof. Lowry's work is among the best of its kind, and anyone who 

 could claim to have read it through and absorbed its contents would cer- 

 tainly have a very good knowledge of inorganic chemistry. 



F. A. Mason, 



Isotopes. By F. W. Aston, D.Sc, F.R.S., Fellow of Trinity College, Cam- 

 bridge. [Pp. viii + 152.] (London : Edward Arnold & Co., 1922. 

 Price 95. net.) 



In collecting and publishing in book form the results of recent researches 

 on the measurement of atomic weights by the methods of positive ray 

 analysis. Dr. Aston has done a real service to aU students of physics and 

 chemistry. 



The subject is treated in historical sequence, so that the first isotopes 

 considered are those belonging to the radio-active elements. After an excel- 

 lent summary of the work in this field the author discusses in greater detail 

 the light which positive ray experiments have thrown on the nature of the 

 so-called elements. He describes first Sir J. J. Thomson's parabola method, 

 which resulted in the discovery that neon was not an element of atomic 

 weight 20-2, but a mixture of two isotopes of atomic weights 20 and 22, but 

 with exactly the same chemical properties. The need for an instrument of 

 greater precision led Dr. Aston to design the mass-spectrograph with which 

 atomic weights can be measured with an accuracy of one part in a thousand. 

 The instrument is described in detail, and the description leaves the reader 

 marvelling at the ingenuity and experimental skill of the author. The 

 results so far obtained with this instrument are collected together, and are 

 of far-reaching importance to physical and chemical theory. Comparatively 

 few of the elements examined are simple ; by far the greater proportion are 

 mixtures of isotopes, the number of the isotopes varying widely. Great 

 stress is laid on the fact that, if oxygen be taken as an element of atomic 

 weight i6'00, the other elements examined have atomic weights which are 

 exact whole numbers or are mixtures of isotopes whose atomic weights 

 are whole numbers. The only certain exception to tliis whole-number rule 



