September 11, 1908] 



SCIENCE 



345 



mere heat evolved is not a true measure of the 

 driving force of a chemical reaction, chem- 

 istry has felt an ever-growing need of accurate 

 determinations of that vehich is the true meas- 

 ure, the free energy. A knowledge of this 

 quantity permits the theoretical chemist to 

 predict the direction in which a reaction will 

 proceed or the state of equilibrium to which it 

 will arrive, and enables the technical chemist 

 to calculate the possible yield in a given man- 

 ufacture, or the amount of work obtainable 

 from a given process. 



The present volume is by far the most im- 

 portant contribution towards this end which 

 has as yet been made. It is a book written 

 to technical chemists by an acknowledged 

 master of technical chemistry, but it will 

 doubtless find a larger audience among the 

 uncommercial chemists; especially in this 

 country where a broad knowledge of thermo- 

 dynamics is not yet regarded as indispensable 

 in the training of the chemical engineer. 



The first three chapters deal with the the- 

 orems of thermodynamics and the development 

 of the general free energy equation. In the 

 fourth and fifth chapters comes the exhaustive 

 discussion of the conditions of equilibrium in 

 such important reactions as the water-gas 

 process, the Deacon process and the formation 

 from the elements of water, carbon dioxide, 

 ammonia and the halogen acids. The sixth 

 chapter critically summarizes all the existing 

 data on the specific heat of gases, which must 

 be known if we are to calculate the free 

 energy at one temperature from that at an- 

 other. The last chapter treats in detail the 

 experimental methods which have been em- 

 ployed in the study of gaseous equilibria. 



After a single perusal of the book the 

 reader may not appreciate the infinite pains, 

 or the critical acumen amounting nearly to 

 inspiration, with which the author has ex- 

 tracted the truth from a great mass of uncer- 

 tain and frequently contradictory experimental 

 material. His sxiccess in this task has been 

 demonstrated several times since the appear- 

 ance of the German edition by new experi- 

 mental investigations which have fully cor- 

 roborated his conclusions. 



The English edition, an excellent transla- 

 tion, contains additional matter in the form 

 of three appendices. The first reviews the 

 new and sensational method proposed by 

 Nernst for the calculation of chemical equilib- 

 rium from thermal data. The second gives 

 in detail the results of experiments carried 

 on in the laboratories of Nernst and the 

 author on the free energy of formation of 

 carbon dioxide and water, of experiments by 

 Lewis on the electromotive force of the oxy- 

 hydrogen cell, and of others by Lewis and 

 Falkenstein on the Deacon process. The 

 third appendix contains a miscellany of short 

 notes dealing chiefiy with the reaction velocity 

 in gaseous systems. 



To all who are interested in making chem- 

 istry an exact science, and who are not unwill- 

 ing to read a book requiring a little thought 

 and study, this work is heartily commended. 



Gilbert N. Lewis 



Handhooh of Flower Pollination. By Dr. 



Paul Knuth; translated by J. E. AiNS- 



WORTH Davis. Vol. 2. Oxford, Clarendon 



Press. 1908. 



For many years Hermann Miiller's " Fer- 

 tilization of Flowers by Insects," which had 

 been translated into English, was the stand- 

 ard reference-book on all subjects connected 

 with the relation of flowers to their insect- 

 visitors. It was, however, getting very much 

 out-of-date; so Dr. Paul Knuth, taking it as 

 a basis, undertook the preparation of a new 

 work, intended to include all the information 

 available up to the date of publication. The 

 new " Handbuch der Bliitenbiologie " could 

 not be included, ILl^e Miiller's work, in a single 

 volume, so it was divided into several sections. 

 The first of these consisted of a general intro- 

 duction ; then came an account of the observa- 

 tions made in Europe ; and finally, those from 

 other parts of the world were to be given. 

 Knuth did not live to see the last section pub- 

 lished, but it was brought to a satisfactory 

 completion in 1905 under the editorship of 

 Dr. Ernst Loew. 



There was naturally a demand for an Eng- 

 lish translation of the " Handbuch," and this 



