460 



NA TURE 



[March 16, 1905 



Hololainpra, Saussure, 1864, replaces the more 

 familiar Aphlcbia, Brunner, 1865. 



But this catalotjue should be received less with 

 criticism than with jTratitude to the painstaking 

 author, and we hope the second volume will appear 

 at an earlv date; it will doubtless include such 

 omissions as have been unavoidable in the first 

 volume, owinsj to the time necessarv for publication. 



M. B. 



I'lrccutage Tables for Elementary Analysis. By Leo 

 F. Guttmann, Ph.D. Pp. 43. (London : Whi'ttaker 

 and Co., 1904.) Price 3$. net. 

 This book is only intended to facilitate the calcula- 

 tion of the results of an ordinary organic analysis, 

 and its title, therefore, is somewhat misleading. It 

 is stated that " the tables have been carefully 

 calculated and checked, they are therefore absolutely 

 accurate." After this statement, ^ nothing is left to 

 us but to see if they are likely to be useful, .^fter 

 careful consideration of this question we are com- 

 pelled to give an unfavourable reply. If vve have 

 the analvtical result that 01 173 gr. of a substance 

 gave 0-2869 gr. carbon dioxide, we can, in the 

 ordinary course of things, by looking out the 

 logarithm of 0-2869, adding the easily remembered 

 logs, of 12/44 ^nd of 100, and subtracting the log. of 

 01173, get the log. of the percentage. But according 

 to the tables before us, we look out a number 

 corresponding to 0-117 and 0-28. We then look again 

 for a number corresponding to 01 18 and 0-28. We 

 subtract the two numbers, multiply by 0.3 by means 

 of another table, and subtract this result from 

 the first number looked out. We next find a 

 number corresponding to o. 117 and 0-69, divide by 

 100 and add this result, and thus, after four 

 references to tables, two arithmetical operations in 

 the head, one subtraction and one addition on paper, 

 we get our percentage. .\ppeal to . a chemist 

 constantly engaged in organic analysis has only 

 confirmed the view that these tables are unlikely to 

 save time or to promote exactitude in the calculation of 

 organic analyses. A. S. 



Ho'w to Photograph 'di'ith Roll and Cut Films. " The 

 Amateur Photographer " Library, No. 30. By 

 John A. Hodges. Pp. xviii+i2o. (London: 

 Hazell, Watson, and \"iney, Ltd., 1904.) Price is. 

 net. 

 TiiK ever increasing number of photographers and 

 more especially amateurs, who work with either roll 

 or cut films, will find in these pages all the necessary 

 information for the production of pictures. The 

 author does not pretend to have written a treatise on 

 the whole art and science of photography, but he has 

 given a straightforward account of the various oper- 

 ations that have to be completed to ensure good 

 results. The treatment is well suited for amateurs, 

 and the numerous well reproduced illustrations serve 

 admirably to render many points clear. 

 The Telescope. By Thomas Nolan. (New York . 

 D. Van Nostrand Company, 1904.) Price 50 cents. 

 Thk first edition of this small treatise on the 

 elementary principles of optics as applied to telescopes 

 appeared in 18S1. In the present issue the author has 

 left this matter practically as it first appeared, with 

 onlv one or two minor corrections, but has added a 

 chapter describing in a brief manner the advances 

 that have since been made. .At the end is also given 

 a bibliography relating to the telescope, which will be 

 of service to those who wish to study more in detail 

 different branches of the subject to which slight 

 references only have been given. The book is 

 published in the Van Noslrand Science Series, and 

 should prove a useful addition. 



NO. 1846, VOL. 71 ] 



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 Infection of Laboratories by Radium. 



In ;i rpcpnt attempt in thf physics liuilding of Mtdill 

 University to make electroscopes with a very small natural 

 leak, repeated failures were encountered. The rate of dis- 

 charge of several instrunienls, carefully made, was found 

 to be about sixty to one hundred times as large as that 

 obtained by Mr. H. L. Cooke two years earlier in the same 

 building. At first it was supposed that the insulation of 

 the sulphur bead was defective. But the natural leak was 

 large and unaffected when the upper support of the sulphur 

 bead was raised to a higher potential than the gold leaf 

 system, so that the insulation was not at fault. Nor was 

 the rate of discharge altered when the electroscope was 

 entirely surrounded by lead one inch thick. Removal to 

 another building produced no effect on the leak of the 

 electroscope. It appeared probable that the trouble was 

 due to the radio-activity of the materials from which the 

 electroscope was made. A rude instrument, made in a 

 private house with a tobacco tin, the amber mouthpiece of 

 a pipe, and a cork, was found to give better results than 

 the most carefully constructed instrument in the physics 

 building. Some electroscopes were next made in th^- 

 chemistry building, using materials which had never been 

 into the physics building. Instruments with a very slow 

 rate of discharge were now easily manufactured. These 

 were used to test materials from various parts of the physics 

 building, and it was found that all were infected with 

 excited activity. Sheets of mica, lead foil, iron, zinc and 

 tin were all active, even when taken from drawers or 

 cupboards. 



Of the substances tested, the only one which showed no 

 activitv was some thin Dutch metal leaf kept between tissue 

 paper in a closed drawer. .About qo per cent, of the excited 

 activitv could be removed from the metal sheets by strong 

 hydrochloric acid, but the activity was transferred to the 

 solution. It waa also possible to volatilise a portion of the 

 deposit by raising the metal sheet to a red-heat in a Bunsen 

 flame. Both a and $ rays were detected, but it was diffi- 

 cult to measure their exact proportion. The natural leak 

 of an electroscope was increased to a measurable extent 

 when a mica window was replaced by one cut from a sheet 

 of mica kept in the physics building. 



The difficulty of conducting radio-active experiments in 

 rooms where strong preparations of radium were present 

 was early observed by ^ladame Curie, and later bv Elster 

 and Geitel, but the present experiments seem to show that 

 the effect may be widely spread. The emanation from 

 radium used in the large physics building has passed bv 

 convection and diffusion into various rooms. In a few da\- 

 each fresh supply of emanation is transformed into the rapidlv 

 changing substances radium .\, B, and C. The further 

 changes of the products of radium have been investigated bv 

 Prof. Rutherford, and described by him in his Bakerian 

 lecture {Phil. Trans., vol. cciv., pp. ibg-aic)), and in a 

 recent letter to N.\TURE (February 12). In the former he has 

 pointed out that bodies exposed to the air in the open will 

 be covered with an invisible film of radio-active matter of 

 very slow rate of change, and that the strong radio-activitv 

 observed in a room in which radium preparations have 

 once been used is probably due to the deposit on the walls 

 of the room of this slowly decaying matter from the emana- 

 tion. In his letter to N.ature, he has shown that radium 

 (' gives rise to radium D, and that the further change to 

 F is rayless in character and attains half value in fortv 

 years. The further change to F emits $ rays, and reaches 

 half value in six days, whilst the change from F to the 

 final product is accompanied with o rays, reaching half 

 value in 150 days. 



The o and $ rays emitted by the coating on the materials 

 in the physics building are doubtless due to the changes 

 above mentioned. If the supply of emanation were arrested 

 at the present date, the activity already deposited would 

 rise to a maximum in two or three years, and then gradu- 



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