478 



NATURE 



[June 8, 191 1 



MODERN GAS MANUFACTURE. 

 A Text-Book of Gas Manufacture for Students. By 

 J. Hornby. Sixth edition, revised and enlarged. 

 Pp. xi + 423. (London: G. Bell and Sons, Ltd., 

 191 1.) Price 7^. 6d. net. 



THE fact that a sixth edition of Mr. Hornby's 

 text-book wap needed is the most convincing 

 proof of its excellence, more especially as the readers 

 to whom it appeals are necessarily limited in number, 

 and other text-books on the subject exist. 



The many alterations and advances which have 

 taken place in fjas manufacture durinjj the past ten 

 years have rendered it imperative to remodel the book 

 so as to deal with the various types of vortical retort 

 which are beings introduced, and the use of increased 

 charges for horizontals, which are found to give 

 substantial improvement in the quantity and quality 

 of both gas and tar. 



The author disclaims any intention of making the 

 book an exhaustive treatise on the subject, but in 

 point of fact he so nearly attains this level that it is 

 a pity he has not gone a little more fully into the 

 theoretical aspect of carbonisation as gleaned from 

 his own experience, rather than to rely on quotations 

 from the work of others, which, although in most 

 part excellent, sometimes give a wrong impression. 



For instance, in speaking of the effect of distilla- 

 tion at low temperature, he quotes a paragraph from 

 Dr. Lunge's work on " Coal Tar and Ammonia," to 

 the effect that amongst the liquid, watery products 

 "acetic acid is paramount," which, although true to 

 a certain extent of the products obtained from lignite 

 and peat, gives a wrong impression of the liquor 

 obtained at low temperature from an ordinary gas 

 coal. 



After a brief general sketch of the usual procedure 

 in a gas works, the author deals in the first chapter 

 with the formation and general characteristics of the 

 various classes of coal, and in discussing the conver- 

 sion of vegetable deposits into coal, represents the 

 complete reaction of fermentation and decav on cellu- 

 lose bv the beautifully simple equation, 



2(C,H,,OJ=5CO, + 5CH, + C„ 

 which certainly does not take into account the feelings 

 of the supporters of any dehydration theories. In 

 discussing the caking coals, it would be worth while in 

 a future edition to mention at anv rate the influence 

 of the percentage of oxygen on' the gas vield and 

 coking properties of various coals. 



In the second chapter the wide subject of carbonisa- 

 tion is attacked, and here the description of the 

 gaseous products of distillation due to primary and 

 secondary actions are not quite in accord with the 

 more modern views on the subject, but the remainder 

 of this and the next chapter are verv well done, and 

 t-he reader is given next a section on labour-saving 

 appliances, amongst which inclined and vertical retort 

 settings are dealt with. 



The diagrams of the Dessau, Woodall-Duckham, 

 and Glover-West retorts are excellent, and it is a 

 pity that the author has not dealt more fully 

 with the relative advantages and drawbacks of 

 these systems. There is but little doubt that the 

 NO. 2 171, VOL. 86] 



continuous systems of carbonisation as represented 

 by the two latter retorts gives the nearest approach 

 to a uniform treatment of coal that is to be found, 

 and that when the general arrangements have ■ 

 perfected by experience they will show theni^ 

 to be far superior to their Continental foreru: 

 the intermittent Dessau retort. 



The author's treatment of the modern practice of 

 filling the retorts with the charge so as to leave no 

 space at the top of the retort, and extending the 

 period of carbonisation is insufficient, and the two 

 reasons which he gives for the improved results 

 obtained are not nearly so important as that the mass 

 of coal provides a cool and easy escape for the hydro- 

 carbon and other gases distilling from the portions 

 in contact with the hot walls, and so prevent"? thr 

 destruction of valuable illuminaiHt;s. 



In this part of the work also some noti> ^ i 



to be taken of Mr. Glover's Norwich chamber retorts, 

 which for the same reason give excellent results. 



It would have been of great advantage to the work 

 if the author had compiled with care a table con- 

 trasting the results obtained by the various methods 

 of carbonisation from the horizontal retort with small 

 charges and high heats to the latest types of sloper 

 chamber ovens. 



In the appendix on the " Distillation of Tar," the 

 author gives the specific gravity of ordinary tar as 

 ranging from i'i2 to i"i6. Is this a relic of the days 

 when the gas manager was content with 10,000 cubic 

 feet of .gas per ton of coal, or is it an up-to-date figure 

 from the vertical retorts and modern processes? Has 

 the author never come across that tar, which a large 

 proportion of our gasworks are making, in which, 

 owing to the degree to which the temperature ha? 

 been pushed to obtain a large yield of gas, the 

 specific gravity has been raised to 12 and above, and 

 the value reduced almost to nil? 



Perhaps the most serious fault that can be found 

 with this text-book is that little or no attention is 

 paid to the subject of the thermal value of gas. The 

 dav is rapidly approaching when illuminating value 

 will be superseded by calorific value as the test for 

 the quality of gas, when the calorie and thermal unit 

 will be as important to the gas manager as the candle 

 standard is now, and a text-book for the rising gene- 

 ration of gas engineers should certainly deal in full 

 with the subject of how best to transfer the greatest 

 heat value from the coal to the gas. 



THE DELI XE ATI OX OF THE EARTH'S 

 SURFACE. 

 Maps and Map-making. By E. A. Reeves. Pp. 

 xiii+145. (London: Royal Geographical Society, 

 19 10.) Price 6s. net. 



THE course of instruction in surveying and map- 

 making offered to students and travellers by 

 the Royal Geographical Society is justly esteemed for 

 its useful and practical character. A book on this 

 subject by Mr. Reeves, the map curator of the society, 

 who has for many years carried out the instruction, 

 and under whose direction the system of teaching has 



