NATURE 



[July 6, 191 1 



the water cooling- of the engine parts, the various 

 methods of ignition, and the principles of opera- 

 tion. Then follows a section on the arrange- 

 ment of a gas-engine installation and the testing of 

 the plant, whilst the two concluding chapters contain 

 a good description of the various methods used for 

 the governing of the engine and of the use of gas 

 producers. 



The book is stated on the title-page to be by the 

 two authors mentioned in the heading to this review, 

 and it is therefore puzzling on pp. i, no, and 152 

 to find " the author " only referred to. Possibly the 

 book was written in sections, and this explanation 

 appears plausible by reason of the curious contradic- 

 tions that occur in it. Thus, on p. 1 it is stated that 

 " the modern gas engine is a prime mover, perfectly 

 reliable, cheaper in first cost, including the gas pro- 

 ducer, than a steam engine and its boiler " ; whereas 

 on p. 21, we learn "the capital cost of the gas-engine 

 plant is much greater than that of the steam-turbine 

 plant," and on p. 152 that "the modern gas engine 

 is very nearly as reliable a machine as a steam 

 engine." 



These statements should not all of them appear in 

 one publication, as, even if explicable by some verbal 

 modification, they tend to confuse the non-expert 

 readers for whom this book is intended. It is this 

 very use by the non-expert that renders slips in ex- 

 plaining the theory of the engine very unfortunate. 

 On p. 5 an unlucky oversight has led to the statement 

 appearing that if "pressure be kept constant the 

 volume will vary as to absolute pressure." Again, the 

 author or authors in stating (on p. 7) that "only a 

 certain proportion of a given quantity of heat can be 

 converted into work," neglect such a well-known fact 

 that the heat conveyed to a gas to keep its expansion 

 isothermal is all of it converted then and there into 

 work. 



These are matters which should be put right in a 

 second edition, and, in view of the very thorough 

 knowledge shown of the practical working of the 

 engine and of the misfortunes to which it is some- 

 times liable, it is likely that there will be a large 

 number of persons to whom the book will be of such 

 value as to render a second edition a necessity. The 

 description of the mode of working of the Clerk 

 engine is specially good, and the letterpress is well 

 illustrated. The authors commit themselves on p. 94 

 to an interesting prophecy concerning the probable 

 future development of the gas engine. 



"It seems likely," they say, " that in the future 

 large gas-engine plants will be designed with engines 

 working on two-stroke cycles, but, instead of each 

 engine having its own charging pumps, a central set 

 of independently driven pumps for gas and air will be 

 provided " ; " these pumps," they suggest, " will prob- 

 ably be of the turbine type, and of greater efficiency 

 than is obtainable with pumps forming an inl 

 part of the engine." 



Finally, we welcome the book as an interesting 

 addition to the less ambitious side of gas-engine litera- 

 ture, and foresee a useful place for it in the library of 

 many persons who wish lo learn something of this 

 growingh; important prime-mover. 

 NO. J 175, VOL. 87] 



RESINS, RUBBER, AND ESSENTIAL OILS. 

 Allen's Commercial Organic Analysis. A Treatise on 

 the Properties, Modes of Assaying, and Proximate 

 Analytical Examination of the Various Organic 

 Chemicals and Products Employed in the Arts, 

 Manufactures, Medicine, csre. With Concise 

 Methods for the Detection and Estimation of their 

 Impurities, Adulterations, and Products of Decom- 

 position. Edited by W. A. Davis and S. S. Sadtler. 

 Vol. iv., Resins, India-Rubber, Rubber Substitutes, 

 and Gutta-Percha, &c. Fourth edition, entirely 

 rewritten. By the editor and the following con- 

 tributors, M. B. Bladder, E. W. Lewis, T. M. 

 Lowry, E. C. Parry, H. Leffmann, and C. H. 

 Lowall. Pp. viii + 466. (London : J. and A. 

 Churchill, 191 1.) Price 215. net. 



THE general characters of the new issue of Allen's 

 work have been described in the notices of 

 earlier volumes reviewed in this journal (Nature, 

 vol. lxxxv., pp. 37, 365). In this connection therefore 

 it is only necessary to remark that the present volume 

 is notable among its fellows for the rather large pro- 

 portion of theoretical and descriptive chemistry which 

 it contains. 



Many users of the book, however, will probably 

 find this a convenience. Considerable advances have 

 been made in the chemistry of the resins and essential 

 oils since the publication of the earlier editions, and 

 many of the results have not hitherto been brought 

 together. Taken with the numerous references sup- 

 plied, the articles upon the three groups of products 

 dealt with in the book — namely, resins, india-rubber, 

 and essential oils — form an excellent summary of the 

 general and analytical chemistry of these products. 

 The following are a few out of many interesting 

 matters to be found in the volume. 



Thanks largely to the work of Tschirch and his 

 coadjutors, it is now possible to make at least a pro- 

 visional attempt at a satisfactory classification of the 

 resins. The proximate constituents of these bodies, 

 so far as they are yet known, may be divided into (1) 

 Resin-esters and their decomposition products; (2) 

 Resinolic or Resin acids; and (3) Rescues ; the last 

 being oxygenated compounds with no very character- 

 istic chemical properties beyond the attribute — a very 

 valuable one — of resistance to the action of alkalies. 

 In many of the resins one or other of these three 

 classes is the preponderating constituent, whence three 

 groups can be distinguished, namely, ester-resins, 

 acid-resins, and resenc-rcsins. The first group, for 

 instance, includes (among others), gum benzoin, 

 storax, "dragon's blood," ammoniacum. and asafce- 

 tida ; in the second group are the coniferous resins 

 and copaiba balsam ; and in the groups of resene-resins 

 are included myrrh, olibanum, dammar, and Manila 

 copal. From a number of the ester-resins the alcohol 

 of the ester has been isolated, and Tschirch distin- 

 guishes two kinds of these alcohols — resinols and 

 resinotannols. The former are colourless, and give 

 no reaction for tannin when tested with iron salts; 

 the latter are coloured and give a tannin-reaction. 

 For the general analytical examination of resins, the 

 acid, saponification, iodine, methoxyl, and acetyl 



