2 22 



NA TURE 



[July 7, 1904 



The sixth and seventh sections contain instructions for 

 mineral analysis, and one is struck by the very com- 

 plete account given of methods by which the decom- 

 position of the mineral is effected by heating in a 

 current of gas, e.g. oxygen, hydrochloric acid, or 

 bromine. The eighth section is taken up with silicate 

 analysis, whilst the concluding section gives an account 

 of the estimation and separation of the halogens and of 

 many other analyses which do not naturally find a 

 place in the earlier portions of the work. 



.\lthough it is clear that the author has taken great 

 pains in the preparation of his book, it may be 

 questioned as to whether the selection of exercises has 

 been uniformly judicious, and as to whether the 

 author's own processes do not occupy a too prominent 

 position, so leading to the exclusion of standard 

 methods of analysis with which every student should 

 be familiar. For example, the author's process for the 

 separation of manganese and zinc by means of 

 hydrogen peroxide in alkaline solution, although found 

 unsatisfactory by other investigators, is fully described 

 to the practical exclusion of the more usual method. 

 The same criticism applies to the larger proportion 

 of the other " hydrogen peroxide separations " which 

 here figure so largely. Again, in the section dealing 

 with silicate analysis, the author's methods of decom- 

 position, especially the one employing boric anhydride, 

 are given at great length, whilst the ordinary method 

 of alkali-carbonate fusion, which is constantly em- 

 ployed both in technical and scientific analyses, is given 

 in a not very happily modified form, and in a sub- 

 ordinate position. 



.Mthough the book presents very many excellent 

 features, and should, when used in conjunction with 

 other works, be of great value, it is hardly considered 

 Mkely that a student who derives his information solely 

 from this source would possess a competent knowledge 

 of the general methods of analytical chemistry. 



H. D. D. 

 Practical Slide Making. By G. T. Harris, F.R.P.S. 

 Pp. 134. (London : Iliffe and Sons, Ltd., 1904.) 

 Price IX. net. 

 Nearly every photographer at some time or another 

 makes his own lantern slides, and so numerous are the 

 methods available, and so varied are the results that 

 can be obtained, that another handbook on the subject 

 is very welcome. In these pages the author success- 

 fully attempts to supply trustworthy information on 

 the subject in a concise form, describing the best 

 known methods for obtaining these transparencies. 

 He lays stress on the great efficiency of some of the 

 older processes, and with the hope that they may be 

 revived he includes them in this book. The first two 

 chapters deal with the apparatus for exposing the plate, 

 and the remainder treat of the development by the 

 several methods described, and of the various other 

 manipulations required before the slide can be con- 

 sidered properly finished. No pains seem to have been 

 spared to obtain accuracy in the formulas and to render 

 clear the methods of procedure, so that the book forms 

 a trustworthy guide. 



Botany Rambles. Part ii. hi the Summer. By Ella 

 Thomson. Pp. 130. (London : Horace Marshall 

 and Son, 1904.) Price is. 

 The young learners for whom this little book is intended 

 are urged persistently to see for themselves, by exam- 

 ining plants, that what is told them in the lessons is 

 true. They are instructed in simple language how to 

 set about this work of verification and are urged to 

 make use of their own eyes to find out additional facts 

 for themselves. It is evident that the writer under- 

 stands children and knows how to arrest their interested 

 attention. 



NO. t8io, vol, 70] 



LETTERS TO THE EDITOR. 



'The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Exradio Spectrum. 



From a private communication from Mr. Ba.\endall, I 

 learn that he has noticed the following correspondences 

 between the spectrum of the emanation from radium 

 (exradio) and the spectra of " bright line stars " (Campbell, 

 Ast. and Ast. Phys.. vol. .\iii. p. 468) :— 



" Exradio " Bright Line Stars 



'^''"""°- (Campbell). 



5805 S813 



5595 5593* 



4690 4688 



4650 4652 



4630 4633 



With the exception of 5593*, these stellar lines are all 

 strong and characteristic. Another of the exradio lines. 

 5137, may correspond with 5135. 



I am very ignorant of stellar spectra, and send this note 

 merely to direct attention to a possible correspondence. 



University College. William Ramsay. 



The Occurrence of Radium with Uranium. 

 A LITTLE time back, Mr. B. B. Boltwood published in this 

 Journal (May 26, p. 80) a preliminary notice of an investi- 

 gation of the ratio of uranium to radium in various minerals. 

 I have for some time been engaged in a similar investi- 

 gation, which, though the results are not yet matured, 

 seems to be leading to the conclusion that this ratio is 

 constant, as in Mr. Boltwood 's experiments. An interest- 

 ing case is the mineral torbernite, or copper uranite. This 

 mineral forms transparent green tetragonal crystals the 

 composition of which is accurately represented by the 

 formula Cu0.2U03.P30s.8H,0. The substance dissolves 

 easily in sulphuric acid, forming a perfectly clear green 

 solution. This solution, when boiled, gives the radium 

 emanation, and the quantity of emanation produced in one 

 day is about the same as that yielded by the same weight 

 of Joachimsthal pitchblende. The percentage of uranium is 

 also about the same. If the radium in this mineral has 

 been produced since the formation of the mineral (and the 

 recent quantitative experiments of Sir W. Ramsay and Mr. 

 Soddy on the absolute rate of production of the emanation 

 seem to make that certain), there is practically no choice 

 as to what the parent substance should be. Uranium is 

 the only candidate. The great complexity of most of the 

 radio-active minerals may make it difficult to obtain con- 

 clusive evidence by studying them. But here there seems 

 to be no alternative but to conclude that uranium is the 

 parent. R. J. Strutt. 



Residual Affinity. 



Sir Oliver Lodge's highly suggestive letter (June 23, 

 p. 176) will be welcome to the many chemists who have 

 been endeavouring to interpret chemical phenomena in 

 terms of the electronic theory of the physicist. The pro- 

 position that the " Faraday tube " may be subdivided 

 would appear to be capable of being widely applied in con- 

 nection with many of the most interesting phenomena of 

 chemistry. Thus not only would the existence of water of 

 crystallisation and the formation of so-called molecular 

 compounds be thereby brought into line with the more 

 tvpical manifestations of valency, as pointed out in Sir 

 Oliver's letter, but it would appear that it may possibly 

 enable the hitherto conflicting hydrate and dissociation 

 theories of solution to be harmonised. Thus in the case 

 of an electrolyte such as sodium chloride, we should in the 

 dry state regard the sodium atom united to the chlorine 

 atom by means of a Faraday tube or bundle, as it may 

 more appropriately be designated, the union leading to the 

 great stability of the compound as such. On the addition 

 of water, however, some of the constituent fibres or strands 

 of the bundle become deflerted in such a way that the sodium 



