594 



NATURE 



[January 6, 192 1 



times unavoidable. In the present case it seems 

 a pity that M. d'Ocagne's later notation has not 

 been accepted as standard and used wherever pos- 

 sible. By later notation is meant the one adopted 

 in that writer's "Calcul Graphique et Xomo- 

 graphie " (1908). It is wonderfully concise, with- 

 out any sacrifice of clarity or completeness, and 

 is quite simple to grasp. M. d'Ocagne evidently 

 considers it an improvement on the more cum- 

 brous notation of his earlier "Traite de Xomo- 

 graphie" (1899), as he has Continued to use it 

 in his latest brochure, " Principes usuels de Nomo- 

 graphic avec application k divers problfemes con- 

 cernant rArtillerie et I'Aviation " (1920). 



Metallurgy for Dental Surgeons. 



A Manual on Dental Metallurgy. By Ernest A. 

 Smith. Fourth edition. Pp. xvi + 285. (Lon- 

 don : J. and A. Churchill, 1920.) Price 125. 6d. 

 net. 



SMITH'S "Dental Metallurgy" is read by so 

 many dental students that the goodness or 

 badness of the text has a considerable influence 

 on the stage of knowledge of the embryo surgeon- 

 dentist. Thus for many years it was impossible, 

 even with the help of photomicrographs showing 

 the two metals in patches like the stripes on a 

 zebra, to convince the dental student that a eutec- 

 tic was a mixure, because the author of this book 

 had declared that such a patchwork might be a 

 chemical compound ! This error has, fortunately, 

 been corrected in the new edition, which shows 

 many useful improvements resulting from the in- 

 corporation of the rudiments of modem scientific 

 metallurgy. 



In spite of these improvements, the general tone 

 of the book is still unsatisfactory, and carries 

 with it the impression that the dental surgeon is 

 content with a much lower standard of knowledge 

 than are his medical colleagues. Thus, in view of 

 the fact that for many years every candidate for 

 the L.D.S. has had to pass an examination in 

 elementary chemistry before taking the test in 

 dental metallurgy, it is almost incredible that a 

 standard text-book should attempt to teach metal- 

 lurgy without making use of chemical equations. 

 It is, nevertheless, true that the author has de- 

 scribed the extraction of the metals from their ores 

 (for which formulae are usually given) without in 

 any instance providing a chemical equation to 

 express the action which takes place ; it must 

 therefore be taken as a singular compliment to 

 the work on dental amalgams, carried out in the 

 Laboratory of Physical Chemistry at Bristol a 

 short time before the war, that it has provided 

 NO. 2671, VOL. 106] 



the author with the only example of a chemical 

 equation which the reviewer has been able- to dis- 

 cover in the whole of the volume. This treatment 

 of the subject can, however, scarcely be regarded 

 as a compliment to the dental profession; and> 

 even if it represented a reasonable point of view 

 when the first edition appeared in i8g8, the time 

 has surely come when dental text-books should be 

 addressed to readers with some knowledge of 

 elementary science, instead of being lowered to 

 the standard of a trade-class of mechanics or 

 plumbers. T. M. L. 



Our Bookshelf. 



Peat Industry Reference Book. By F. T. 

 Gissing. Pp. xxiv -I- 292. (London : Charles 

 Griffin and Co., Ltd., 1920.) Price 7s. 6d. 



The author, alone or in conjunction with 

 Bjorling, has already published two books on 

 peat. The present volume deals mainly with 

 those developments in the peat industry which 

 have arisen since the publication of the previous 

 books. It is divided into eight sections, dealing 

 with the formation of peat, its winning as cut 

 peat, machine-formed peat and pressed peat, peat 

 gas and its by-products, power gas, peat-moss 

 litter, peat mull and other products, such as 

 alcohol and paper obtainable from peat. The 

 eighth, and last, section contains miscellaneous 

 information, formulae, and tables, which will be of 

 much use to persons dealing with peat. 



The various processes patented, or worked on 

 an experimental scale, have been faithfully de- 

 scribed from the point of view of the inventors 

 or exploiters of these processes, and it is this 

 circumstance which constitutes the chief defect of 

 the book. Claims which are experimentally un- 

 justifiable are occasionally admitted into the book 

 without criticism, and for this reason some of the 

 statements made are quite at variance with the 

 actual facts, and are likely to mislead readers un- 

 acquainted with the properties of peat. Everyone 

 knows, for instance, that a peat-pulping machine 

 exerts practically no cutting action on peat, yet 

 the claim that one peat-pulping machine cuts the 

 cells of the peat fibres is passed without comment. 



Again, under another process it is stated that 

 wet raw peat contains 20 per cent, of dry peat, 

 and gives 8 per cent, of charcoal. As a matter of 

 fact, wet raw peat from an undrained bog con- 

 tains only about 8 per cent, of dry peat, and 

 gives only about 28 per cent, of charcoal, and 

 even from a well-drained bog the amount of char- 

 coal got from 1 00 tons of the raw peat rarely 

 exceeds 3-5 tons. It is evident, too, from this 

 book that some " inventors " are still unable to 

 grasp the elementary fact that in order to obtain 

 100 tons of dry peat from raw peat by the aid of 

 artificial heating somevi'hat more than 100 tons of 

 dry peat must be burnt to develop the heat re- 

 quired. 



