466 



NATURE 



[September 5, 1907 



previous workers, and displayed more than ordinary 

 ingenuity in devising new methods to avoid such 

 errors, and at the same time he paid particular atten- 

 tion to the necessity of employing the purest material 

 in such work. He was never satisfied with even 

 repeated experiments on different amounts by the 

 same method, and always, whenever practicable, 

 adopted two or more independent methods. If we 

 include those elements which he did not completely 

 study, he determined the atomic weights of no fewer 

 than twenty-nine of the elements, and in nearly every 

 case his numbers dilTer little from those now adopted 

 — a remarkable feat for one man working without 

 any assistance. In the course of his investigations 

 he analysed certain of the minerals containing the 

 rare earths, and succeeded in separating two new- 

 elements, ytterbium from gadclinite and gadolinium 

 from samarskite. 



The process of time has brought it about that 

 much of his work begins to have mainly historical 

 interest, and probably at the present day most 

 chemists will feel more vivid interest in researches 

 which were to some extent incidental to the prin- 

 cipal investigation. Prominent among these is his 

 elaborate work relating to the intricate and puzzling 

 problem in analysis presented by titanium, niobium, 

 and tantalum. So difficult is the separation of these 

 three elements, when occurring together in the same 

 substance, that many eminent chemists have 

 imagined the existence of other elements; for 

 instance, Hermann strongly insisted on the presence 

 of ilmenium in samarskite, but Marignac showed 

 it to be really a mixture of niobium and tantalum. 

 Although it cannot be said that he solved the problem 

 with complete success, yet Marignac was the first to 

 devise a method— the differing solubilities in hydro, 

 fluoric acid of the double fluorides of the three 

 elements with potassium— which effected any real 

 separation, and which to this day has not been super- 

 seded by any more satisfactory. The problem is one 

 that still awaits solution, and is occupying the atten- 

 tion of many chemists. It is of interest to note 

 that, in recognition of the method devised by him, the 

 name marignacite was recently assigned by Mr. 

 Weidman and Mr. Lenher to a variety of pyrochlore 

 from Wausau, Wisconsin. Of little less vivid interest 

 is his comprehensive investigation relating to the 

 formula of zirconia and the atomic weight of the 

 element. He made use of the law of isomorphism 

 propounded by Mitscherlich, of which he was early 

 a keen advocate, and undertook a complete chemical 

 and crystallographical examination of a large number 

 of fluozirconates. None of his experiments lent any 

 confirmation to the idea put forward by Svanberg 

 that zirconia contains three distinct metallic oxides. 

 Nevertheless, the question is one deserving of further 

 consideration. Prof. Church and other observers 

 have noted a remarkable range in the density of 

 zircons, 40 to 47, and an even more remarkable 

 alteration in the density effected in certain stones oi 

 low density by the application of heat, and the con- 

 elusion has been drawn that there are three varieties 

 of zircon. Further, the crystallised native zirconia, 

 NO. 1975, VOL. 76] 



baddeleyite, presents almost as wide a range of 

 density, which is even more difficult to understand 

 in the case of an apparently simple oxide. It is 

 possible that zirconium has never been completely 

 isolated; it is well known that a satisfactory method 

 for separating it from titanium has yet to be found. 



Marignac found time to examine the chemical and 

 crystallographical characters of a large number of 

 minerals, and also of artificial salts prepared by him 

 in the laboratory. The sentence with which he opens 

 one of his elaborate papers is indicative of . the 

 thoroughness characterising his work, and embodies 

 a ma.xim which even now is by no means universally 

 appreciated by chemists : — 



" L'interet que presente I'etude des formes 

 cristallines des divers composes chimiques, m'a 

 engag^ h. ne jamais nfSgliger de determiner exacte- 

 ment les formes de ceux qui s'offraient h. moi, en, 

 cristaux d^terminables, dans le cours de mes travaux 

 de laboratoire." 



Towards the end of his career his attention was 

 attracted to the physical side of chemistry, and he 

 carried out with his customary skill and care a 

 lengthy series of thermochemical determinations ; un- 

 fortunately, the complete collapse of his physical 

 vigour brought his work to a premature close. To 

 his other investigations — for instance, on ozone — - 

 space will not permit us to allude. 



As regards the appearance of the volumes, the 

 quality of the paper and the style of the printing 

 are beyond criticism, and care has been taken to 

 indicate the original pagination. Most of the papers 

 were published in the Bibliothcque Universelle de 

 Geneve or the Annales de Chimie et de Physique; 

 those dealing with mineralogical subjects appeared 

 in the Annales des Mines. 



THE BLOOD-SUCKING GNATS. 

 A Monograph of the Culicidae or Mosquitoes. Mainly 

 Compiled from Collections received at the British 

 Museum. Vol. iv. By F. V. Theobald. Pp. 

 xix + 639; 16 plates. (London : Printed by order of 

 the Trustees, 1907. Sold by Lx)ngmans and Co., 

 B. Quaritch, Dulau and Co., and at the British 

 Museum [Natural History].) Price i2. 12s. 6d. 



THIS work forms the second supplementary volume 

 to Mr. Theobald's original monograph of the 

 Culicidae of the world, in two volumes, published by 

 the trustees of the British Museum in igoi. The 

 present volume deals very largely with the new species 

 which have been added to the national collections, 

 and besides these it also embodies the descriptions of 

 one hundred and sixty species which have been de- 

 scribed by various arlhors since the issue of the first 

 supplementary volume in 1903. 



It would be difficult to overestimate the great 

 scientific valur K Mr. Theobald's most e.xhaustive 

 faunistic work on these insects. It is a model of 

 painstaking scientific accuracy, and we congratulate 

 him on its issue. 



With the exception of the adoption of a few 

 characters in an admirable scheme of general 



