S98 



SCIENCE. 



[N. S. Vol. VIII. No. 200. 



■quire much attention, extend over a long period, 

 .and are often failures owing to conditions that 

 require experience to foresee and control. Some 

 f the experiments require technical knowledge 

 nd skill not to be expected of the average 

 pupil who presents himself for this class of 

 work, as, for example, where the directions say 

 to determine the nitrogen by Kjeldahl's method 

 or by Stutzer's method, and with a reference to 

 a, chemical treatise proceeds to the next step in 

 the experiment as if the quantitative determi- 

 nation of nitrogen were an everyday affair in a 

 botanical laboratory. 



But these defects, or limitations, may be dis- 

 missed as not impairing the usefulness of the 

 ■work, if it be understood at the outset that the 

 l)ook is not adapted to seriatim study by the 

 classes of any institution, unless it be those of 

 the author, at least not those in any American 

 institution. But a suflicient wealth of material 

 is provided so that the instructor may select 

 what best suits his purpose, and under this 

 eclectic system the work must commend itself 

 as highly satisfactory and serviceable. 



J. C. Arthur. 



Quantitative Chemical Analysis by Electrolysis. 

 By De. Alexander Classen, Privy-Coun- 

 cillor, Professor of electro-chemistry and in- 

 organic chemistry in the Koyal School of 

 Technology at Aachen ; in cooperation with 

 Dr. Walter Lob, lecturer on electro-chem- 

 istry in the Eoyal School of Technology at 

 Aachen. Authorized translation, third Eng- 

 lish fiom the revised and greatly enlarged 

 fourth German edition, by William Hale 

 Herrick, A.m., formerly professor of chem- 

 istry in Iowa College and in the Pennsylvania 

 State College, and Bertram B. Boltwood, 

 Ph.D., instructor in analytical chemistry in 

 the Sheffield Scientific School of Yale Uni- 

 versity. New York, John Wiley & Sons ; 

 London, Chapman & Hall. 1898. Pp. 301. 

 The earlier editions of Classen's book are so 

 well known that it is only necessary to call atten- 

 tion to the difference between this and preced- 

 ing editions. The book is greatly improved by 

 the introductory chapter on the theory of elec- 

 tro-chemistry. Says the author in his preface: 

 "The present edition, revised with the assist" 



ance of Dr. Lob, differs from the previous 

 editions in that the introduction has been aug- 

 mented by the insertion of a section devoted to 

 theory. This was made the more necessary 

 since the investigations of recent years have 

 been chiefly devoted to the explanation of 

 reactions in solutions and the determination of 

 electrical magnitudes." This chapter deals 

 with the theory of electrolytic dissociation, the 

 laws of Faraday and Ohm, the significance of 

 tension, current strength, and resistance, the 

 theory of electrolytic precipitation. 



The remainder of the ' general part ' of the 

 book takes up the methods of measuring the 

 strength of the current, the measurement of 

 current tension, the sources of current, includ- 

 ing primary and secondary batteries, and phys- 

 ical means of producing the current, such as 

 electro-magnetic machines and thermopiles. 

 Given the means of producing, regulating and 

 measuring the current, it remains to apply the 

 methods to the precipitation and separation of 

 the metals. These are described in the ' special 

 part ' of the book, and it is safe to say that 

 most of the best electro-chemical methods are 

 included here. The appendix contains a num- 

 ber of practical examples of electro-chemical 

 analysis. 



This book comes from one of the leading 

 authorities, and is generally recognized as a 

 standard in the field which it covers. 



H. C. J. 



Introduction to Electro-chemical Experiments. By 



Dr. Felix Oettel. Translated by Edgae 



F. Smith, Philadelphia, P. Blakiston, Son 



& Co. 1897. Pp. 143. 

 Practical Exercises in Electro-chemistry. By Dk. 



Felix Oettel. Translated by Edgar F. 



Smith. Philadelphia, P. Blakiston, Son & 



Co. 1897. Pp. 92. 



The first of these two little books by Oettel 

 deals with the conditions necessary for electro- 

 chemical experiments, such as sources of the 

 current, methods of measuring the current, in- 

 cluding different forms of the voltameter and 

 galvanometer, and methods of measuring pres- 

 sure. The arrangement of apparatus and elec- 

 trolyte in carrying out an experiment is then 

 taken up. This is followed by a brief discus- 



