NA TURE 



271 



THURSDAY, MAY 



1910. 



CRYSTALLOGRAPHIC RESEARCHES. 



Crystalline Structure and Chemical Constitution. By 

 Dr. A. E. H. Tutton, F.R.S. Pp. viii+204. 

 (London : Macmillan and Co., Ltd., 1910.) Price 

 55. net. 



THE series of science monographs projected by 

 Messrs. Macmillan and Co. has opened aus- 

 piciously with a fascinating account by Dr. Tutton of 

 the exhaustive cr\-stallographical researches upon 

 which, for the past twenty years, he has been engaged. 

 It is a goodly story that he has to tell, and well is it 

 told; without wearymg the reader with an unwieldv 

 mass of details, he pr^ents in all essential completeness 

 a vivid picture of an unusually coherent series of in- 

 vestigations. The immensity of the labour involved 

 can be fully appreciated only by those who may have 

 undertaken work of somewhat similar character, but 

 the most casual reader can scarcely fail to be amazed 

 at the extraordinary amount of work the author has 

 contrived to squeeze into the leisure hours of a busy 

 official life; by strenuously utilising every spare 

 moment he has found time to accomplish a task 

 which has set an ideal of what a complete study of 

 the physical properties of crystallised substances 

 should be. Those at least who have at heart Eng- 

 land's position in the world of science are grateful 

 to Dr. Tutton that, thanks largely to his efforts, 

 in crystallography, at any rate, she stands so 

 high. 



Dr. Tutton completed his scientific training, and 

 \\ as looking round for a field for research at an oppor- 

 tune moment. It was at that time being increasingly 

 felt by those speculating on the molecular arrange- 

 ment of crystals that little real advance could be made 

 towards a solution of the problem uatil more numer- 

 ous and more accurate measurements of crystallised 

 substances, especially those constituting isomorphous 

 groups, were available. Principal Miers had already 

 published his important memoir upon the characters 

 of the red-silver minerals, pyrargyrite and proustite. 

 From that and similar work it seemed clear that 

 small, but perceptible, differences existed between the 

 crystalline forms of the constituents of an isomor- 

 phous series ; in fact, the conclusion established by 

 Dr. Tutton 's investigations was not so wholly unfore- 

 seen at that date as might be supposed from the 

 opening pages of his book. It was, however, very 

 desirable that research of a similar, and, if possible, 

 more comprehensive, character should be extended to 

 artificial salts, because in such the purity of the 

 material, and the perfection of the crystals, could be 

 secured with far greater certainty than when the 

 process had been in nature's unfettered control. To 

 an investigation of this kind Dr. Tutton determined 

 to devote himself, and he selected for his initial task 

 the three members containing potassium, rubidium, 

 and caesium of the isomorphous group of which 

 K2Mg(SOj26H.O may be taken as a t\-pe; their 

 NO. 2 1 14, VOL. 83] 



crystalline form had not previously been properly 

 studied. 



It was part of Dr. Tutton 's design that his re- 

 search should be carried out with instruments as 

 perfect as mechanical skill could produce. He found, 

 indeed, at hand a most efficient goniometer for the 

 measurement of interfacial angles of crj'stals, but, 

 when he came to the determination of the optical and 

 other vectorial characters, he was compelled to design 

 an entirely novel equipment, since nothing of the 

 requisite standard had hitherto been constructed. 

 The first of these instruments was a grinding and 

 cutting goniometer, by means of which it was pos- 

 sible to prepare sections and prisms with absolute 

 confidence in the accuracy of their orientation in the 

 crystal. The natural faces are seldom suitably 

 developed for optical research, and the lapidaries' 

 method was far too untrustworthy for Dr. Tutton 's 

 standard. This apparatus naturally called for a com- 

 panion instrument, which should provide light of any 

 desired colour at will. Sodium light, which is adopted 

 as the standard in all measurements of refractivity, 

 is, of course, readily available, but no optical investi- 

 gation can be considered complete unless the colour 

 dispersion has also been studied ; previously crystallo- 

 graphers h'ad been restricted to the lithium and 

 thallium flames, of which the latter is actually poison- 

 ous, and, moreover, the study of interference figures 

 often demanded light of intermediate wave-lengths. 

 Dr. Tutton accordingly designed a most efficient 

 monochromatic illuminator, in which the dispersive 

 agent is a single prism of very dense glass. Spurred 

 by the success achieved, he proceeded next to plan, 

 using the principle of the interference of light, an 

 instrument of extraordinary delicacy for the measure- 

 ment of variations in length. He himself employed 

 it in conjunction with the necessary- additional appar- 

 atus, which he fully describes, for the measurement of 

 thermal expansion and elasticity constants, and an 

 interferometer of his design was recently installed in 

 the Standards Department of the Board of Trade 

 (Nature, vol. Ixxxii., p. 338). The whole of Dr. 

 Tutton 's instrumental apparatus has been characterised 

 by the painstaking care bestowed upon those appar- 

 ently small details which have such an important 

 bearing upon efficiency of performance. 



As already stated, Dr. Tutton opened his researches 

 with a study of the crystalline form of the double 

 sulphates of potassium, rubidium, and caesium, with 

 magnesium. He subsequently extended his investiga- 

 tion to similar compounds of ammonium and thallium, 

 which were found to possess closely related proper- 

 ties, and also to the corresponding selenates. Up to 

 date he has studied the sulphates and selenates, and 

 many of the double sulphates and selenates with 

 magnesium, zinc, iron, nickel, cobalt, copper, man- 

 ganese, and cadmium. Altogether forty-four salts — 

 Dr. Tutton gives the number as fifty-four, but appears 

 to have inadvertently reckoned ten of them twice — 

 have been prepared and investigated, the greatest 

 possible care being taken to ensure their purity and 

 perfection of development ; no fewer than 25,000 



L 



