3 10 



NATURE 



[November 20, 1919 



volume, a volume which undoubtedly will take a 

 high rank among modern text-books of zoological 

 science. It is something better than a mere text- 

 book of embryology, as it deals very fully with 

 many of the 'most important principles of bio- 

 logical philosophy, and will prove very useful as 

 a guide for practical research work in other 

 branches of zoological science. S. J. H. 



THE RARER ELEMENTS. 



(1) The Analysis of Minerals and Ores of the 

 Rarer Elements for Analytical Chemists, 

 Metallurgists, and Advanced Students. By Dr. 

 W. R. Schoeller and A. R. Powell. (Griffin's 

 Scientific Text-books.) Pp. x + 239. (London: 

 Charles Griffin and Co., Ltd., 1919-) Price i6s. 

 net. 



(2) The Metals of the Rare Earths. By Dr. James 

 Frederick Spencer. (Monographs on Inorganic 

 and Physical Chemistry.) Pp. x + 279. (Lon- 

 don: Longmans, Green, and Co., 1919.) Price 

 I2S. 6d. net. 



THE two volumes before us, taken together, 

 form a very complete treatise on the rarer 

 elements, their occurrence, properties, and the 

 methods for their separation. .A^lthough they 

 overlap in some measure, each contains much in- 

 formation of the highest importance at the 

 present day. 



The practical value of many of the rarer 

 elements has recently been brought into pro- 

 minence, and it is becoming increasingly plain 

 that, locked up in these little-known minerals 

 widely distributed over the earth's surface, there 

 are elements possessing properties of hitherto 

 unrealised value and importance. 



Radium has shaken the old conceptions in 

 chemistry and physics to their very foundations. 

 Uranium, tungsten, tantalum, molybdenum have 

 given us steels which have profoundly influenced 

 the engineering trades and the production of 

 artillery. Thorium and cerium have preserved the 

 gas industry as a means of illumination. Cerium 

 and the rare earth metals rendered us almost 

 independent of the lucifer match. These are but 

 a few indications of the potential value of the 

 rarer elements. 



(i) This volume, which naturally comes first, 

 deals exhaustivelv with the minerals from which 

 the rarer elements are derived, and gives very 

 clear and practical instructions for their recogni- 

 tion, and the properties, chemical reactions, and 

 method for separating the elements. The design 

 of the work is distinctly original, and the authors 

 have included as much trustworthy information 

 about each element as is available at the present 

 time, together with descriptions of the spectro- 

 scopic, magnetic, electroscopic, and other ap- 

 paratus used in research. It is abundantly clear 

 that they have a very practical acquaintance with 

 their subject ; novel chemical and physical re- 

 actions are given that are apparently taken direct 

 from the laboratory note-books. 



The elements are taken in the order of their 

 NO. 2612, VOL. 104] 



groups in the periodic system, and the text is 

 arranged under two headings — "General Informa- 

 tion," which includes spectroscopic and other 

 physical reactions; and "Mineral Analysis," in- 

 cluding qualitative and quantitative estimations- 

 and chemical reactions. 



There is no general index, but in its place two 

 lists are produced, one giving the names of nearly 

 two hundred minerals containing rare elements, 

 and the other the various methods for separating 

 them from the bodies most frequently accompany- 

 ing them. 



A table of atomic weights and gravimetric 

 factors is included. 



(2) The title of this volume strikes one as a 

 little inappropriate, for the metallic properties of 

 the rare earth elements are those about which 

 least is known, but the author is to be congratu- 

 lated upon having collected together the essential 

 details of all that is known in the domain of the 

 "Rare Earths." 



This field has a fascination of its own, quite 

 apart from any utilitarian considerations ; that is 

 only realised by those who have worked in it; so 

 great is that fascination that it ha^ claimed the 

 best energy of some of the most honoured men of 

 science. Berzelius, Nilson, Cleve, Lecoq de Bois- 

 baudran, Delafountain, Moissan, Crookes, Urbain 

 are only a few that have fallen under the spell of 

 the "Rare Earths." The work, hitherto exceed- 

 ingly difficult on account of the rarity of the 

 minerals needed, has been greatly facilitated by 

 the development of the " mantle " industry, 

 because in the extraction of the very large quan- 

 tities of thorium and cerium needed for that 

 purpose, all the members of the rare earth grou]} 

 are thrown out as by-products, and can be pro- 

 cured with comparative ease. 



The substantial monograph under notice is a?i 

 advance upon any of the excellent works that 

 have recently appeared on the subject. The most 

 remarkable feature in the volume is the great 

 number of references to authorities that are given ; 

 these number as many as 1029, and will be found 

 of very great value to the student, enabling him 

 easily to consult the original memoir. 



The author's remarks, though good, are some- 

 times liable to be misleading; in this connection 

 we notice that, in reviewing the work of the late 

 Sir William Crookes on the rare earths, and the 

 suggestion there put out as to the possible exist- 

 ence of "meta-elements," the author states^ on 

 page 7 that Crookes, by fractional precipitation, 

 obtained seven fractions of different basicity which 

 had different absorption spectra, which he called 

 meta-elements. This may be a clerical error by 

 the use of the term "absorption" instead of 

 "phosphorescence," for the matter is quite cor- 

 rectly stated on page 66. 



In point of fact, Crookes's contention was that 

 the purest yttria obtainable gave under the 

 cathodic discharge, in vacuo, a discontinuous spec- 

 trum consisting in numerous more or less nebulous 

 coloured bands, and that by fractionating this 

 material it was possible to separate these band* 



