I 



164 



NATURE 



[December 15, 1904 



high-class public secondary schools. We must be prepared 

 to face a great financial sacrifice, for some years at any 

 rate, if we were to put secondary education in this country 

 on anything lilce the level it had reached in America, 

 Switzerland, and Germany. After other speakers had put 

 forward similar claims for consideration of the subject. Lord 

 Londonderry, in reply, said that he felt the weight of the 

 arguments put forward, but the opinions of his colleagues 

 of the Board of Education and himself on this vitally im- 

 portant matter were expressed in such detail and so de- 

 finitelv in the reply forwarded by Mr. Morant to the chamber 

 on .September 26 (see Nature, October 13, p. 595) that on 

 the present occasion he proposed to devote attention rather 

 to the question of commercial education than to that of 

 technical education. The whole matter was one to which 

 the Board were fully alive, and he was very glad to learn 

 from the representations which they had made that day 

 that there was on the part of the chambers of commerce 

 a keen appreciation of the value of that special advanced 

 instruction in the several sections of mercantile practice 

 which the Board had felt it their duty to encourage in the 

 evening schools serving the more important commercial 

 communities. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, February 1 1. — " On Cerlain Properties of 

 the .Alloys of Silver and Cadmium." By Dr. T. K. Rose. 



Attention was directed to these alloys on account of the 

 advantages of using them as the material for trial plates 

 for testing the fineness of silver coin and plate. .An ex- 

 amination of the curves of equilibrium between the liquid 

 and solid states of the alloys proved the existence of several 

 compounds of silver and cadmium, some of which have 

 already been recognised in other ways. Horizontal branches 

 of the curve mark the solidification of the compounds 

 Ag,Cd,, AgCd, and AgCd^, and the solidification of AgjCdj 

 corresponds to a cusp on the curve of initial freezing points. 



There is a strong tendency for mixtures of the compounds 

 to form solid solutions. This is strikingly shown in the 

 case of alloys containing more than 80 per cent, of silver. 

 At temperatures in the short range of a few degrees between 

 the initial and final freezing points of these alloys, two 

 bodies exist side by side, but at a lower temperature they 

 coalesce to form a single solid solution provided that 

 sufficient time is allowed for complete mixing by diffusion. 

 For example, in the standard alloy, which contains 75 per 

 cent, of cadmium, solidification begins at about 94,°, and 

 is completed at about 913°. If the alloy is maintained at 

 some temperature between these points a network of a silver- 

 poor body is gradually formed surrounding crystals of a 

 silver-rich body. If the alloy is subjected for some hours 

 to a temperature a little below 913°, large crystals with 

 regular boundaries are formed occupying the whole area of 

 the field. These alloys are remarkably ductile. 



The alloy corresponding to the formula .Ag,Cd is fine- 

 grained and apparently homogeneous. If heated for some 

 time to a temperature of 750°, somewhat below its point 

 of solidification, the cadmium from the surface is volatilised, 

 leaving a layer of pure silver. On removing this during 

 the operation of polishing a black layer is met with, coloured 

 by oxide of cadmium, and underneath this the original alloy 

 is found to exist. The layers are not everywhere of the 

 same thickness, so that in the course of polishing alternate 

 rings of black and white are produced, resembling the well 

 known Japanese decorative metal-work called Mokum^, 

 which is used in jewellery. 



The alloy containing about 50 per cent, of silver consists 

 of crystals of a silver-rich body, often pinkish in colour, set 

 in a white matrix composed of AgCd,. The 40 per cent, 

 alloy is a hard, brittle substance, the compound Ag,Cd,. 

 As the percentage of silver decreases, a matrix, consisting 

 mainly of AgCd,, makes its appearance surrounding the 

 crystals of Ag.Cd,, and specimens containing less than 

 25 per cent, of silver consist of crystals of AgCd, set in a 

 matrix of cadmium. 



Several similarities to the silver-zinc series of alloys have 

 been noted. 



NO. 1833, VOL. 71] 



November 24. — " The Refractive Indices of the 

 Elements." By Clive Cuthbertson. 



In a letter addressed to Nature in October, 1902, atten- 

 tion was directed to the fact that the refractivities of the 

 five inert gases of the atmosphere, He, Ne, A, Kr, and X, 

 as determined by Ramsay and Travers, were, within narrow 

 limits of accuracy, in the proportion of i, 2, 8, 12 and 20; 

 or, more simply, of 5, 5, 2, 3, and 5. 



In a second letter it was shown that the refractivities of 

 the halogens, CI, Br, and I, stand also in the relation of 

 2, 3, and 5 to the same degree of accuracy ; but it was 

 pointed out that the figures for P, .As, and S, as measured 

 by M. Le Roux in 1861, did not show any similar relation; 

 and it was observed that a re-determination of them would 

 be interesting. 



With a Jamin's refractometer, adapted for use with high 

 temperatures, results have now been obtained for Hg, P, 

 and S, which differ widely from those of M. Le Roux. The 

 index of mercury, calculated for a molecule containing two 

 atoms, is placed at i 001857, a number which agrees closely 

 with the value given by the refractive equivalent of Glad- 

 stone. The index of P^ is found to be 1001197, and that of 

 Sj is looiioi. 



In all three cases it is estimated that the margin of error 

 does not exceed ij per cent. Comparing these values for 

 P. and S, with those of N, and Oj, it is shown that the 

 simple relations found in the case of the inert gases and 

 the halogens also hold in the case of nitrogen and phos- 

 phorus, oxygen and sulphur ; and that an atom of phos- 

 phorus retards light four times as much as an atom of 

 nitrogen, an atom of sulphur four times as much as an 

 atom of oxygen. 



Efforts have also been made to measure the index of 

 fluorine in the gaseous state, but, owing to the experimental 

 difficulties, success has not yet been attained. 



It appears then, that, out of fourteen elements the index 

 of refraction of which has been measured in the gaseous 

 state, twelve conform to the rule that in each chemical 

 group the refractivities of the elements are in the ratios of 

 small integers. The other two, Hg and H, have no allied 

 elements with which they can be compared. 



It is pointed out that N, O, and Ne are each followed, in 

 their respective families, by an element the refractivity of 

 which is four times as great, and that, consequently, there 

 are reasons for believing that the elements composing the 

 series N, O, F, and Ne, and P, S, CI, and A are, in some 

 sense, homologous. Comparing the refractivities of the 

 latter series we see that the power to retard light appears 

 to be closely connected with the valency, increasing as it 

 increases, in spite of the decrease in atomic weight, as 

 shown in the following table : — 



Atomic weight ... 31 32 



Refractivity ... 299x4 275 x 



The series Ne, O, N, show the same relation, and it is 

 probable that the refractivitv of C is even higher than that 

 of N. 



The refractivity of B, estimated from BCI, and BBr,, is 

 certainly very great ; but whether it exceeds that of C 

 there is not sufficient evidence to determine. 



December i. — " On the Structure and Affinities of Fossil 

 Plants from the Palaeozoic Rocks.— V. On a New Type of 

 Sphenophvllaceous Cone (Sphenopliylhim fertile) from the 

 Lower Coal-measures." Bv Dr. D. H. Scott, F.R.S. 



The class Sphenophyllales, of which the fossil described 

 is a new representative, shows on the one hand clear 

 affinities with the Equisetales, while on the other it 

 approaches the Lycopods ; some botanists have endeavoured 

 to trace a relation to the ferns. The nearest allies among 

 recent plants are probably the Psilotacen:, which some 

 writers have even proposed to include in the Sphenophyllales. 



The new strobilus appears to find its natural place in the 

 tvpe-genus Sphenophyllum, as at present constituted, but 

 it possesses peculiar features of considerable importance, 

 which may probably ultimately justify generic separation. 

 The specimen, of which a number of transverse and longi- 

 tudinal sections have been prepared by Mr. Lomax, is from 

 one of the calcareous nodules of the Lower Coal-measures 



