690 



SCIENCE 



[N. S. Vol. XXXIX. No. 1010 



" Javel water." Originally it meant the liquor 

 prepared by action of clilorine on dilute 

 potasli solution. In so far as its bleaching 

 effect is concerned such a liquor is essentially 

 a solution of potassium hypochlorite. It was 

 inevitable, however, that when, through the 

 cheapening of sodium compounds, potassium 

 hypochlorite was superseded by the sodium 

 salt, the name popularly applied to the 

 bleaching liquor should undergo a change in 

 signification. The fact that sodium hypo- 

 chlorite solution was already employed in 

 pharmacy under the name of Labarraque's 

 liquor could not affect this change. Phar- 

 maceutical language is too esoteric and popu- 

 lar habit too persistent to render it possible 

 for the pharmaceutical term to supplant the 

 established usage of the textile trade. I take 

 it, then, that we must expect the sodium hypo- 

 chlorite-chloride mixture to continue to be 

 known as " Javel water." Such confused 

 statements, however, as the following — ^let us 

 hope a slip of the pen — are not to be excused 

 even in a writer whose subject is one relating 

 to textile chemistry. It occurs at p. 234 of 

 Pellew's " Dyes and Dyeing," an excellent 

 popularizing exposition of the triumphs of 

 synthetic chemistry in this fascinating field: 



The potash and soda compounds, known respec- 

 tively as Labarraque's solution and Javelle water, 

 are less active and powerful than bleaching 

 powder, but have the same general properties. 



It is to be hoped that Mr. Pellew's readers 

 will not be misled by either his definitions 

 or his spelling. 



J. P. Snell 



Macdonald College, 

 Quebec, Canada, 

 February 27, 1914 



SCIENTIFIC BOOKS 



Manual of PetrograpMc Methods. By Albert 

 JoHANNSEN, Ph.D., Assistant Professor of 

 Petrology, the University of Chicago. New 

 York, McGraw-HiU Book Co. 677 pages, 

 770 figures in text and as whole page plates. 

 $6.00 net. 

 The methods of microscopic petrography, 



like other laboratory methods, have advanced 



steadily in number and in complication dur- 

 ing the fifty years of their practise, keeping 

 pace with the increasing number of workers, 

 the aim at greater accuracy and the develop- 

 ments of the petrographic microscope and its 

 accessories. The author states in the preface 

 that " the desire of an increasing number of 

 students for more complete information in 

 regard to modern petrographic-microscopic 

 methods than is to be found in any English 

 work on the subject " has led to the prepara- 

 tion of this book, but the reviewer knows no 

 more complete and up-to-date treatment of 

 this special subject in any language, for in 

 most cases such works combine the general 

 and theoretical part with a description of the 

 individual minerals, while in this work only 

 the methods are dealt with, but with a 

 thoroughness, especially regarding the appli- 

 cations of optical mineralogy, which is of 

 great value to the advanced student and in- 

 vestigator. Beginning with a short introduc- 

 tory chapter on crystallography and a thor- 

 ough treatment of stereographic projection (so 

 necessary for some of the more recent micro- 

 scopic methods), chapters follow on the trans- 

 mission of light through crystals, with a very 

 complete and practical treatment of such 

 topics as lenses, the petrographic microscope 

 and the innumerable accessories which are now 

 available, while the following chapters, com- 

 prising 300 pages, or nearly half the book, give 

 a very complete account of the practical meth- 

 ods of application of the principles and instru- 

 ments previously described. A somewhat 

 briefer but sufficient account of the determina- 

 tion of specific gravity, mechanical separation 

 of rock minerals, microchemical reactions, 

 preparation of thin sections, etc., fills the re- 

 maining pages. The book is clearly printed 

 and compact, , notwithstanding the extended 

 text and many figures; it represents a vast 

 amount of careful, discriminating and con- 

 structive work on the author's part, as, for 

 instance, is shown by the bibliography at the 

 end of each chapter, and should be invaluable 

 in its special field. 



John E. "Wolff 

 Harvaed Univeksity 



