300 Scientific Intelligence. 



3. Chemical Reactions and their Equations; by Ingo W. D. 

 Hackh. 12mo, pp. 138. Philadelphia, 1921 (P. Blakiston's 

 Son & Co. Price $1.35 net) . — This little book has been prepared 

 for the use of students in connection with the writing of chemical 

 equations. The fundamental ideas about symbols, atoms, mole- 

 cules, ions, formulas, valency, valence numbers, oxidation and 

 reduction, etc., are very clearl^^ presented, and then the principles 

 of chemical reactions and their equations are well discussed. 

 The book presents no less than 446 consecutively numbered 

 equations which cover the various types very fully. Considerable 

 attention is paid to ionic equations, but a great many are given 

 in the molecular form. The book may be regarded as a very 

 useful and satisfactory one for its purpose, but it appears that 

 it might be made still better if some discussion were given in 

 regard to reversible reactions, and also if precipitates and volatile 

 products were indicated in some- way in the equations, and if 

 reactions of gases or vapors and of fused or ignited substances 

 were distinguished by parenthetical notes from those taking 

 place in solutions. For instance, the equation of an important 

 metallurgical reaction, 2PbO + PbS ^ 3Pb -\- SOg, which is 

 given without note or comment, might lead the student to suppose 

 incorrectly that this would happen at ordinary temperature. 

 Again, it appears that the equation 2NaCl + H^O = Na^O + 

 2HC1 of a reaction that is familiar in connection with the ' ' salt- 

 glazing" of pottery where the salt is volatilized, should be written 

 with the sign of reversibility and that the high temperature 

 required should be noted. h. l. w. 



4. Food Products, Their Source, Chemistry and Use; by 

 E. H. S. Bailey. 8vo, pp. 551. Philadelphia, 1921 (P. Blakis- 

 ton's Son & Co. Price $2.50 net). — This is the second, revised 

 edition of a useful book for students and general readers dealing 

 with a subject of the greatest importance to mankind. A very 

 extensive list of edible products is discussed in connection with 

 their origin and production, their manufacture, composition, 

 food-value, digestibility, adulteration, etc. 



The book is supplied with ninety-two appropriate illustrations. 

 It gives a vast amount of valuable and interesting information, 

 not only about the foods commonly used in this country, but also 

 concerning the important products of other parts of the world. 

 The subject of beverages, including water, is well treated, but 

 the discussion of alcoholic drinks has been considerably abbre- 

 viated, in comparison with the previous edition, because the 

 manufacture of these liquors is now of much less importance 

 than formerly. h. l. w. 



5. Discussion on Isotopes. — A discussion participated in by 

 Sir Joseph Thomson, Dr. Aston, Professors Soddy, Merton and 

 Lindeman at the March meeting of the Royal Society is inter- 



