;S 



NATURE 



[July 13, 191 1 



of his own generation, there is no doubt that some 

 such action, if only on grounds of public convenience, 

 is necessary, and it is more than probable that Austra- 

 lians of another generation will be grateful for the 

 prescription of a stereotyped list of names. 



THE CHEMISTRY OF CALCAREOUS 

 CEMENTS. 

 The Chemistry of Testing of Cement. By Dr. C. H. 

 Desch. Pp. xi + 267. (London: E. Arnold, 1911.) 

 Price 10s. 6d. net. 



THE "cement" treated of in this volume is the 

 group of calcareous cements — that is, the plastic 

 materials employed to produce adhesion between 

 stones and bricks in the construction of buildings and 

 engineering works. The book deals, shortly but 

 clearly, with the manufacture of the various kinds of 

 calcareous cements, with their components, constitu- 

 tion, and properties, and with the mechanical and 

 chemical methods of testing them. 



Owing to the extending employment of concrete 

 the production of cement is becoming more and more 

 important, and the demands upon its qualities in- 

 creasingly stringent. These more exacting require- 

 ments have so far been met with a remarkable degree 

 of success, partly by improvements in mechanical pro- 

 cesses, but also to no small extent through the co- 

 operation of the chemist. For two reasons the ser- 

 vices of the latter are likely to become of yet greater 

 value in the industry. On one hand a still higher 

 standard of quality may be demanded in the finished 

 product, and, on the other, a larger variety of raw 

 materials may be found to be utilisable in the produc- 

 tion. 



The complex character of the substances entering 

 into the composition of calcareous cements, and the 

 obstacles in the way of ready experiment with the 

 products, have in the past greatly limited our know- 

 ledge of the chemical reactions which occur in the 

 making and "setting" of these bodies. In modern 

 practice, however, two things are helping to shed light 

 upon the dark places. One is the introduction of 

 "etching" methods, similar to those employed In 

 metallography, for studying the structure of cements 

 in their various phases ; the other is the conception 

 of cements as, essentially, colloids. Both these 

 matters are fully explained and their importance em- 

 phasised in the volume before us. 



The view adopted by the author as to what takes 

 place during the setting of Portland cement is sub- 

 stantially that of Dr. Michaelis. Assuming for the 

 purpose of discussion that the cement materials con- 

 sist of lime, alumina, and silica only, then the essen- 

 tial hydraulic constituent, alite, is formed from these 

 by the action of heat during the process of manufac- 

 ture. It is regarded as a solid solution of calcium 

 silicates and aluminates. When water is added to the 

 cement, it partly decomposes the alite, hydrolysing the 

 aluminates in the first instance. The solution thus 

 produced is a supersaturated one, and it presently de- 

 posits tricalcium aluminate. According to the quan- 

 tity of water in the mixture, the deposit is either 

 mainly colloidal or mainly crystalline; if the propor- 

 NO. 2 176, VOL. 87] 



tion of water is small it favours the production of a 

 colloidal "gel." The excess of lime above that re- 

 quired for tricalcium aluminate remains in solution, 

 or a part may be deposited as crystals of calcium 

 hydroxide. This process is regarded as probably cor- 

 responding with the " initial set" of the cement. 



As regards the subsequent gradual hardening, the 

 argument is that water acts much more slowly 

 on the calcium silicate contained in alite than 

 on the aluminates, but when hydrolysis docs 

 occur the calcium silicate separates out in 

 the colloidal form. The gel thus produced forms 

 a coating round the cement particles, protecting them 

 from further direct action of the water. But as the 

 latter slowly diffuses through the colloidal coating, 

 more and more of the alite is slowly hydrolysed, and 

 the lime set free is absorbed by the gel, which thereby 

 increases gradually in density and hardness, and loses 

 its plastic qualities. To this gradual desiccation of 

 the gel, which takes place even when the cement is 

 immersed in water, is due the eventual hardening of 

 the mass. 



Evidence for the actual existence of colloid products 

 in hardened cements is found in the fact that some 

 of the components can be stained with eosin. Etching 

 with acids shows the structure of the unchanged 

 cement in the interior of the particles, around and 

 between which lies the dyed colloidal gel. 



The volume embodies the chief results of modern 

 inquiries into what is admittedly a difficult subject. 

 It is written in a true scientific spirit, and would be 

 an excellent book to place in the hands of a chemist 

 with progressive ideas, who wishes to study carefully 

 the chemistry of calcareous cements. C. S. 



GEOPHYSICS. 

 Physik der Erdc. By Prof. M. P. Rudzki. Pp. 

 viii + 584. (Leipzig: Chr. Herm. Tauchnitz, 1911.) 

 Price 14 marks. 



THE course of lectures at the University of Cracow 

 published by Dr. Rudzki in the book under re- 

 view covers a wide range. The subject-matter lies on 

 the border-line of astronomy, mathematics, geography, 

 and geology, and the lectures have coordinated these 

 different sciences very successfully. By readers in 

 this country, where specialised studies so largely 

 cramp workers into one narrow domain, the book 

 should be greatly appreciated. It is much to be de- 

 sired that more opportunity could be found for similar 

 work in British educational methods; for those who 

 agree with this view Dr- Rudzki's work will prove a 

 useful stimulus. 



In saying that the lectures have successfully co- 

 ordinated the different subjects represented, the re- 

 viewer does not wish to suggest that the treatment 

 is necessarily the happiest from the point of view of 

 a student in this country. For instance, while the 

 mathematical reader will find much to interest him 

 and very little that he cannot follow in the subjects 

 outside his own domain, he will find the mathematical 

 part of the work occasionally incomplete or sketchy. 

 At the same time the reader who is not a professed 

 mathematician must frequently find the mathematics 



