76 Scientific Intelligence. 



of the nature of the solid faces and depends only on the chemical 

 type of the lubricant, varying from one chemical series to 

 another. The parameter b however depends both upon the 

 chemical series and the nature of the solid face. The interpreta- 

 tion of these results is difficult. The authors do not accept the 

 current view that friction is due to interlocking asperities of 

 molar dimensions but rather depends upon molecular attraction 

 across an interface. If asperities are to be considered they must 

 be the atoms and the molecules of the substances. The effect of 

 a tangential force is not merely to move the atoms and molecules 

 in the tangential plane but also to rotate them. 



The mental picture which the authors offer is that the primary 

 film of lubricant consists of a single layer of molecules which 

 have been oriented by the attractive fields of the solids so that 

 their long axes are perpendicular to the solid faces. When two 

 such surfaces are brought together the friction represents the 

 maximum tangential stress which can be supported at some 

 median plane of slip which is an imaginary surface parallel to 

 the surface of the solid. This resistance is obviously conditioned 

 by the attractive field of the solids which must vary rapidly along 

 the normal, and also by the nature of the molecular chain of the 

 lubricant used. — Proc. Roy. Soc. 100, 550, 1922. f. e. b. 



6. Power Alcohol; by G. W. Monier- Williams. Pp. xii, 323. 

 London, 1922 (Henry Frowde and Hodder & Stoughton). — In 

 view of the possible insufficiency of the world's petroleum 

 reserves the investigation of alternative motor fuels is an 

 important subject which is very fully examined in this book. 

 The first chapter passes in review the questions of the supply, the 

 production and the economy of the various motor fuels, and 

 reaches the conclusion that there is strong probability that before 

 many years the supply of gasolene will be permanently unequal 

 to the demand, and that power alcohol has an undoubted future 

 before it as a supplementary if not as a competitive fuel. Chap- 

 ter 2 discusses the way in which various organic constituents of 

 plants are elaborated, and the chemical processes by which sugars 

 are converted into alcohol by the yeasts. Chapter 3 treats of 

 the raw materials from which fermentation alcohol is produced, 

 namely, plants supplying starch, plants containing ready formed 

 sugars, and cellulose, and also of the commercial processes of 

 mashing, saccharification, fermentation and distillation. Chap 

 ter 4 surveys the more important starch or sugar-bearing raw 

 materials from the point of view of yield, availability and related 

 economy of alcohol production. Chapter 5 is devoted to the 

 commercial treatment of cellulose materials for the production of 

 alcohol. Chapter 6 explains the ways of making synthetic alco- 

 hol and its production on a commercial scale. 



Chapter 7 reviews the methods of denaturation and various 



