544 



NATURE 



[June 22, 191 1 



consists of sand or crushed quartz, and in some cases 

 layers of some such oxidising material as polarite or 

 oxidium are used, in addition to sand, as in the ; 

 Candy filter. 



The advantages of this method of filtration seem 

 to be the much more rapid rate at which the water : 

 can be passed through the filters, and consequently j 

 the much smaller area which they occupy, and the j 

 ease and rapidity with which they can be cleaned ! 

 by mechanical means. This effects a great saving of 

 labour, and also does away with the workmen coming 

 in contact with the filtering medium. As regards 

 efficiency, it would appear that these filters are at 

 least as efficient as ordinary sand filters. 



After two very useful chapters on "The Purification 

 of Water by Ozone" and "Water Softening and 

 Household Appliances," two chapters follow on the 

 testing of water. They consist of a discussion of the 

 bacteriological, chemical, and microscopic examina- 

 tion of the raw and filtered waters and the inferences 

 to be drawn from them. 



The bacteriological tests suggested, and the methods 

 of applying them are, however, somewhat open to 

 criticism, and need revision in subsequent editions, 

 and the suggestion that these tests should be under- 

 taken by the water managers themselves (unless 

 specially qualified) is also perhaps not of the happiest. 

 To anyone acquainted with the bacteriological and 

 chemical analysis of water, it will be apparent that 

 unless these tests are carried out by skilled operators 

 errors of execution and judgment are likely to crop 

 up. The growing necessity of dealing with impure 

 and polluted sources of supply renders frequent and 

 careful analysis imperative, and the example of the 

 Metropolitan Water Board and some of the Con- 

 tinental and American water undertakers in appoint- 

 ing a staff of qualified analysts might well be fol- 

 lowed by other bodies. 



As the authors point out, the interpretation of the 

 results of analysis depend largely on local conditions, 

 yet they give a table of the standards of purity re- 

 quired in Britain and America, which, by the way, 

 are not applicable to a very large number of water 

 supplies, and they do not state from what source 

 these standards, in so far as they apply to British 

 supplies, are obtained. 



In the remaining chapters, the book deals with 

 problems of distribution, and, in addition to engineer- 

 ing problems, several pages are devoted to the de- 

 velopment of such growths as crenothrix in the mains 

 and the action of peaty waters on lead. This latter 

 subject was exhaustively investigated by Dr. Houston 

 about fifteen years ago, on behalf of the Local 

 Government Board, and the authors quote exten- 

 sively from his work ; the two kinds of action, plumbo- 

 solvency and erosion, although attributed to different 

 causes, are frequently caused by the same water. 



The authors have surely misunderstood Dr. Hous- 

 ton's work when they state (on p. 324) that erosion, 

 which results in the formation of the hydroxide of 

 lead, has probably no consequences obnoxious to the 

 consumer, for they go on to say that the hydroxide 

 scales away and mixes with the current. The section 

 KO. 2173, VOL. 86] 



concludes with a general discussion on public health in 

 relation to water supply, and an account is given of 

 several outbreaks of cholera and typhoid fever, which 

 have been attributed to that cause. It should have 

 been pointed out, however, that in the case of the 

 epidemics at Belfast, mentioned on p. 348, the water 

 supply was completely exonerated by the H^'nl'li Cdin- 

 mission appointed to inquire into the matt< 



The arrangement of the book is exceediiiK'.^ k>-"u, 

 the type clear, and the numerous diagrams and photo- 

 graphs make the descriptions of the various appliances 

 verv easy to understand. As appendices there are 

 some useful tables of filtration constants and other 

 engineering data, and a concise and well-arranged 

 bibliography of works on water purification. 



Denison B. Byles. 



GERMAN AND FRENCH BOOKS ON 

 CRYSTALLOGRAPHY. 



(i) Lehrbuch der Kristallphysik {mit Ausschluss der 

 Kristalloptik). By Prof. W. Voigt. Pp. xxiv + 964. 

 (Leipzig and Berlin : B. G. Teubner, 1910.) Price 

 30 marks. 



(2) Lemons de Cristallo graphic. By G. Friedel. Pp. 

 V + 310. (Paris: A. Hermann et Fils, 1911.) Price 

 10 francs. 



(3) Die Kristallgrtippen nehst ihren Beziehungen zu 

 den Rautngittcrn. By Prof. E. Sommerfeldt. Pp. 

 vii + 79 (Dresden : T. SteinkopfT, 191 1.) Price 3 

 marks. 



(OTTHIS treatise is based upon the lectures delivered 

 J- for some years past by Prof. Voigt at the 

 University of Gottingen, and it concentrates also into 

 a single volume of 964 pages the original work in phys- 

 ical crystallography other than optical contributed in 

 numerous memoirs during the course of a long and 

 active career. Prof. Voigt's name is, perhaps, most 

 familiar from his work on the elasticity of crj'stals 

 and their piezo- and pyro-electrical properties. These 

 branches of physical crystallography are well repre- 

 sented in the book before usi and the only criticisms 

 that suggest themselves are that Prof. Voigt has not 

 given us more experimental details and illustrations 

 of the interesting forms of apparatus employed in 

 the researches, and that British work in this branch 

 of science, especially the thermal expansion and elas- 

 ticity of crystals, is not referred to. The result of 

 these omissions is that in the first place the book 

 presents a somewhat forbiddingly mathematical 

 aspect, the theoretical and mathematical side vastly 

 predominating and entirely overshadowing the prac- 

 tical experimental side of the subject, and that in the 

 second place a certain narrowness of outlook is in- 

 evitable. 



Having said so much, however, and remembering 

 that Prof. Voigt's chair is that of theoretical physics, 

 the thorough manner in which the subject is dealt 

 with inside these somewhat narrow lines cannot fail 

 to impress the reader. The most valuable considera- 

 tion is, moreover, that we have here brought together 

 for us the facts and theories for which hitherto in- 

 vestigators and students have had to search through 

 the numerous original papers of Prof. Voigt. The 



