228 Scientific Intelligence. 



pany). — This appears to be an -anchanged reprint of the third 

 edition of the book published in 1905. It gives clear explana- 

 tions and numerous examples for practice of a wide variety of 

 calculations, including those dealing with atomic weights, for- 

 mulas and factors, and with gravimetric, volumetric and gas 

 analysis. There are also chapters dealing with calorific power, 

 and electric and electrolytic calculations. An appendix contains 

 a number of useful tables, including four-place logarithms and 

 antilogarithms. 



The book appears to present a satisfactory list of topics in a 

 generally satisfactory manner, but it may be criticized in con- 

 nection with its lack of precept and example in regard to the 

 number of figures that deserve to be given in the results of calcu- 

 lations with approximate numbers. This fault may be found 

 in nearly all the text-books dealing with the subject, and it is 

 noticed here in the hope of bringing about future improvement in 

 this matter. A striking example of this kind is found on page 

 71 of the book where from ''3.0 cc", obtained as the difference 

 between two titrations which are recorded only to the nearest 

 0.1 cc, an amount of K^COo is calculated as ''0.20745 g." Now, 

 leaving out of consideration any accidental errors, since the posi- 

 tive or negative third figure of 3.0 is unknown, the third decimal 

 of the result must be uncertain and hence it is unreasonable to 

 carry the figures of the answer beyond 0.207, while 0.21 would 

 perhaps be a more satisfactory statement of the result. In many 

 other cases the data of problems are treated as exact numbers, 

 although in practice they would be approximate ones. For 

 instance, on page 34 a calculation is based on "0.05 g" of avail- 

 able oxygen. It would have been preferable to state this as 

 0.0500 g in order to show three significant figures and to make 

 the four-figure answers appear reasonable. h. l. w. 



3. Ammonia and the Nitrides; by Edward B. Maxted. 

 12mo, pp. 116. Philadelphia, 1921 (P. Blakiston's Son and Co. 

 Price $2.00 net) . — The first two chapters of this little book give an 

 account of the experimental work and general principles upon 

 which the commercial synthesis of ammonia from gaseous hydro- 

 gen and nitrogen is based. This discussion is largely mathemati- 

 cal, but there are explanations and illustrations of several forms 

 of experimental apparatus. 



The nitrides, nearly all of which may be regarded as derivatives 

 of ammonia, are discussed from a descriptive and historical 

 point of view, and the author calls attention to the meagerness of 

 our knowledge of these important compounds and the desirability 

 of further investigation of them. 



The final chapter of the book gives an excellent account of that 

 interesting modification of a usually very inactive gas called 

 active nitrogen. h. l. w. 



