492 SCIENCE PROGRESS 



attention of the physicist and the physiologist. A complex colloidal system 

 is involved, whilst yet we are but timorously laying down the principles of 

 the colloidal state ; and revolutionary ideas in nutrition demand attention. 



Sir Edward Thorpe, in his editorial introduction to the series of Mono- 

 graphs on Industrial Chemistry, to which this volume is a valuable addition, 

 anticipates that the series will serve to show how fundamental and essential 

 is the relation of principle to practice, and to indicate the bearing of the 

 academic thought of to-day on the industrial chemistry of to-morrow. A 

 monograph that fulfils these precepts will have a wider appeal than one that 

 is merely an exhaustive analysis of the diversity and minutiae of technical 

 manufacture. Mr. Clayton's book deserves this wider audience. 



The author surveys the raw materials of the margarine factory and 

 emphasises the notable advance made by the introduction of hydrogenated 

 fats. He gives a lucid account of the modern processes of manufacture, with 

 descriptions of some types of plant, and describes in detail the analysis of 

 both raw material and finished product. Chapters are devoted to butter, 

 renovated butter, and lard compound. Throughout the text are many refer- 

 ences to the literature and patents, and a considerable bibliography is included. 



All this is required of a purely technological handbook, but the author 

 is interested in the larger problems involved, and turns happily, in the centre 

 of his book, to the difficult task of explaining in a few pages the position of 

 present theories of emulsification. So brief a statement must necessarily 

 leave much unsaid, but it will achieve its purpose if il stimulates to broader 

 thought and to question. Again, in a chapter on Nutritional Chemistry, 

 the author attempts a summary of the present state of knowledge of the 

 " Accessory Food Factors " or " Vitamins," and its bearing on the nutritive 

 value of butter and the various margarines. It is of interest to note that 

 since the publication of this monograph the hard-and-fast line drawn between 

 animal and vegetable fats as regards their content of Vitamin A (adopting 

 the suggested nomenclature of Drummond) has been questioned and the 

 anomalous position of lard explained. 



Margarine will be welcomed by student and technologist, and by all 

 workers in these fields of thought who find interest in the practical applica- 

 tion of knowledge. 



xv. i\. L-. 



The Principles of the Phase Theory : Heterogeneous Equilibria between Salts 

 and their Aqueous Solutions. By Douglas A. Clibbens, Ph.D. 

 [Pp. XX -f 383.] (London : Macmillan & Co., 1920. Price 25s. net.) 



Beyond a certain point the phase theory ceases to have any immediate 

 interest, and presents no new conceptions. Its methods become severely 

 technical, and the whole treatment tends to enter the region of pure geometry. 

 In specialised fields of activity, such as the preparation of salts by the inter- 

 action of other salts in aqueous solutions, a knowledge of the artifices of 

 graphical representation is indispensable to the worker, since it is only by 

 mapping out the whole of the region of states that he can be certain that 

 no unexpected phases have been overlooked. It is to a portion only of this, 

 in itself very specialised, study that Dr. Clibbens has introduced his readers. 

 He has not treated of such cases as the formation of solid solutions, which 

 frequently arise in practice, and the general applications of the phase theory 

 to other systems finds no place in the book. Dr. Clibbens has done the 

 work in an exceedingly able manner, and the diagrams, on folding sheets, 

 are especially to be commended. A good feature of the book is the stress 

 laid on the importance of all parts of the phase diagrams, and not merely 

 of the equilibrium curves. 



Although in its restricted scope the book is in every way excellent, it is 

 not altogether clear to the reviewer for what class of readers it is intended. 



