8o8 



NATURE 



[December i, 1923 



some respects, they are more uwful for purposes of 

 chemical analysis than ordinary luminous spectra ; 

 {/cit<ichrift fiir KUktrochemie, Aug. I, 1923). An 

 itii{x>rtant advantage is the fact that the X-ray 

 trum of an element is <juite independent of the 

 If of the compound containing it which is 

 (•\.uiijne<l. It is easy to detect the presence of an 

 element when only i per cent, is present in a mixture 

 of which not more than i mg. is available. Certain 

 j)roiiiutions arc necessary in examining the X-ray 

 sj)ectra ; although the number of lines for each 

 element is comparatively limited, recent observations 

 have shown the existence of a number of weaker 

 lines; in addition to this, with the high voltages now 

 gfticrally used, not only the spectrum of the first 

 order, but also those of higher orders appear. Slight 

 impurities in the material of the anticathode, and in 

 the substance under examination, also give their lines, 

 so that there are often various possibilities to be 

 considered before a given line can be explained. Not 

 only the wave-length, but also the typical appearance of 

 the suspected lines must be considered, as well as their 

 relative intensity. By measuring photometrically the 

 intensity of the spectral lines it is possible, in some 

 cases, to obtain a quantitative estimate of the amount 

 of an element present in a mixture. The method was 

 used by Hevesy and the author in determining the 

 amount of hafnium in zirconium minerals, and in in- 

 vestigating the chemical properties of the new element. 



Magnetic Records of the British Isles. — The 

 British Meteorological and Magnetic Year Book for 

 1920, published by the Meteorological Office, gives 

 particulars of the diurnal variation of the principal 

 meteorological elements at the Aberdeen, Eskdale- 

 muir, Valencia, and Kew Observatories, with rainfall 

 and sunshine data at Falmouth. The major portion 

 of the volume, however, is devoted to terrestrial 

 magnetism, especially at Eskdalemuir. Two pages 

 are devoted to the diurnal variation of the potential 

 gradient of atmospheric electricity. The results for 

 Kew are based on 10 selected days a month free from 

 negative potential. For Eskdalemuir there are two 

 sets of data, the first derived like the Kew data from 

 days free from negative potential, the second from 

 days when negative potential occurred, although they 

 were comparatively quiet. Taking the first class of 

 days, the mean value of potential gradient at Eskdale- 

 muir for summer (May to August) is practically 

 identical with that at Kew. In the other seasons the 

 Kew value is the greater, the excess being 9 per cent, 

 for the equinoctial and 45 for the winter season. The 

 difference is thus greatest in the months when fog — 

 a recognised source of high potential — is most prevalent 

 in the Thames valley. In addition to the regular 

 tables of hourly values and diurnal inequalities of 

 terrestrial magnetism, there is a discussion by Dr. 

 Crichton Mitchell of different measures of daily 

 magnetic activity at Esltdalemuir. All his criteria 

 make 1920 a quieter year than 1919, and the same 

 conclusion is drawn from the Kew data. There was, 

 however, an exceptionally violent magnetic storm on 

 March 22-23, 1920, during which the range of declina- 

 tion at Kew exceeded 2°. According to the table on 

 p. 47, the fall of westerly declination from 1919 to 

 1920 was 9-9' at Kew, 93' at Valencia, and 90' at 

 Eskdalemuir. Inclination appeared to be practically 

 stationary, while horizontal force showed a slight 

 fall : 77 at Eskdalemuir, 67 at Kew, and 27 at Valencia. 



Photographic Blackening and Coloured Light. 

 —The second number (August) of the Bulletin of 

 the Kir>'u Technical College, Japan, consists of a 

 lengthy and copiously illustrated paper bv Tadaroku 

 Otashiro on " The Relation between the Photographic 



Na 282?, VOL. I I 2I 



' ng and the " 



iins at express. ' incti 



ol wave-length. For thi.s , 



of a plate were exposed t' n 



lights of c>()ual intensity, aiul in other ca^. . tfc 

 wave-length was kept constant and the int<>nsit 

 varied. Ordinary, orthochroma' ,11 



ordinary' plates " dyed " (batl 



erythrosin, cyanin, and pi 



The author theoretically d 

 electric viewpoint the act..... ...,i 



blackening and the wave-length of 1 

 intensity being constant, and expc..,, 

 firms it. " The general form of the fun- 

 independent of the kinds of plat<s tli. 

 sensitising solutions, the time > 

 sensitising solution, the time of •• 

 the developers and the temperature during 

 of development." The eouation includes a " 

 tion factor," and it is shown that there arc 

 maxima and one minimum effect of blackening on ^ 

 continuous exposure to the most effective light 

 and the first maximum corresponds to the end of • 

 period of over-exposure defined by Hurter .1 

 Driffield." He shows that there is a definite relat 

 between the blackening and the strength of 

 solution. The author comes to other iir 

 conclusions, especially, with regard to muli 

 posures, and concludes " that the change 

 plate has been acted on by white light sli..,,;.. 

 essentially the same as that when the plate has h- 

 exposed to the most effective mniuw lirmn.-if i. •■ 

 of light." 



Analysis oi- Coal. — The Fuel Research 1 

 the Department of Scientific and Industrial 1 . 

 has issued through H.M. Stationery Ofiice (15. bd. m 

 Pamphlet No. 2 on the " Physical and Chemical Sur\ 

 of the National Coal Resources." consisting of 

 interim report on " Methods of Analysis of CoaLl 

 The Board has always had in view the physical 

 chemical survey of coal seams in the different mini 

 areas — a task of great magnitude — and the t)olk 

 pursued has been to encourage the formation of lo 

 committees of persons interested in the different 

 fields to which the execution of the survey could 

 delegated. The results of such a survey would 

 greatly depreciated in value unless unity of analy 

 procedure were ensured, and accordingly the ~ 

 asked a committee on sampling and analysis of 

 presided over by Prof. T. Gray, to tabulate a scl 

 of coal analysis which could be uniformly adopted 

 the survey. This pamphlet records their effor 

 The importance is even wider, for most commerc 

 coal testing is confined to the proximate analysL 

 essentially empirical and demanding uniformity 

 practice if discrepant analyses and commercial frict 

 are to be avoided. There is no doubt as to the vj 

 of the report in this direction. Although nothing 

 the kind has been done previously in Great Britr-- 

 the field has already been tilled by American 

 chemists — so well that in many cases the commiv.^^ 

 has been able to adopt their sjjecification without 

 serious modification. This applies particularly to 

 the proximate analysis, and it is likely for that reason 

 that man}' w'ill find no difficulty in adopting the 

 committee's recommendation. Several special and 

 less common methods of coal assay and analysis are 

 included which will add to the usefulness of the 

 pamphlet. A statement of the permissible analytical 

 error is sometimes given, and forms a welcome 

 inclusion. In suggesting a form of report the com- 

 mittee employs a precision of stating results not quite 

 consistent with its own tolerances. The important 

 question of samphng is reserved to a second report. 



