Auc.usr lo, 1905] 



NA TURt 



359 



an explosive may be considered to undergo would only be 

 calculated to convey an erroneous impression regarding the 

 definite nature of the chemical results and their iiniformily 

 under different conditions. 



The paper continues with a description of the experi- 

 ments made to determine the time required for the complete 

 ignition of certain explosives, and also of other experiments 

 to determine the rate at which the exploded gases part 

 with their heat to the walls of the vessels in which they 

 are confined ; and in conclusion it is pointed out that the 

 experiments inade on erosion, with the three explosives 

 referred to in this paper, and with some other explosives, 

 have satisfied the author that the amount of absolute 

 erosion is governed practically entirely by the heat de- 

 veloped by the explosion. 



•• Colours in Metal Glasses, in Metallic Films, and in 

 M.lallic .Solutions." II. By J. C. Maxwell Carnett. 



l-.xpressions, giving the refractive index and the absorp- 

 lii n coefficient (the optical constants) of a compound 

 medium consisting of metal (i) in small spheres (granular), 

 and (2) in discrete molecules (amorphous), diffused through 

 an isotropic non-dispersive transparent medium (the 

 solvent), in terms of the corresponding optical constants 

 of the normal metal, were first obtained. The particular 

 formula-, which apply when the volume proportion (/i) of 

 metal in the compound medium is small, followed imme- 

 diately. By means of these formula? and of the numerical 

 values of the optical constants of gold, silver, and 

 copper for monochromatic light of several different wave- 

 lengths, the values of the corresponding optical constants 

 of diffusions of spheres and of molecules of these metals, in 

 glass, in water, and in vacuo, were calculated and tabu- 

 lated. l"he absorptions of monochromatic light by speci- 

 mens of gold and copper ruby glass and of silver-stained 

 glass were measured. A comparison of the measured 

 absorptions of gold ruby glass with the calculated absorp- 

 tions of gold spheres and of gold molecules diffused in 

 glass, and a collation of the results with others previously 

 published,' show that the colour of gold ruby glass is 

 primarily due to the presence of spheres (not molecules) 

 of the metal. The presence of crystallites, formed by the 

 coagulation of the gold spheres, and reflecting red light, 

 accounts for the irregular blue and purple colours some- 

 times transmitted by gold glass. Further, when the absorp- 

 tions of a colloidal solution of gold in water are compared 

 with the calculated absorptions of gold spheres and mole- 

 cules diffused in water, it appears that colloidal gold 

 consists of small spheres in suspension. 



The close similarity between the observed absorptions of 

 glass stained (amber) with silver, and the calculated 

 absorptions of silver spheres in glass — those of a diffusion 

 of silver molecules in glass are quite different — indicates 

 that the stained region must contain small spheres of silver. 

 The presence of silver spheres (but not of discrete molecules 

 of silver) also accounts for the brilliant blue reflection 

 from the interface between the stained and unstained 

 regions of Stokes's specimens of silver glass. Ehrenhaft's" 

 description of the nature and position of the absorption 

 band observed in the spectrum of colloidal solutions of 

 silver describes so well the position of the absorption band 

 determined by calculation for a diffusion of silver spheres 

 (but not of silver molecules) in water as to justify the con- 

 clusion that the bulk of the silver present in colloidal solu- 

 tion is in the form of small spheres, little, if anv, being 

 in true solution (i.e. molecularly subdivided) ; and this 

 conclusion is confirmed by the fact that the refractive index 

 of a colloidal solution of silver, which was measured by 

 Barus and Schneider, is precisely that which calculation 

 gives as the refractive index of a diffusion of silver spheres 

 (but not of molecules) in water. 



\ comparison of the observed and calculated absorp- 

 tions shows that copper ruby glass owes its colour to the 

 presence in the glass of small spheres of metallic copper ; 

 but some copper molecules are probably also present. 



Calculation proves that diffused spheres of cobalt would 

 give a reddish colour to glass. Cobalt glass is not coloured 

 by the metal in the metallic form. 



1 Phil. Trafis., A, 1904, pp. 385 ei set/. ; Natuice. vol. Ixx. p. 213 (June 

 30, 1Q04). 



- Felix Ehrenhaft, .!«./. ,/er I'hys., vol. x'. p. 48J '1903) 



I 



NO. 1867, VOL. 72] 



The colours produced in geld, silver, and soda glasses 

 by the radiation from the emanation from radium suggest 

 that these glasses contain free ions of the metal, and that 

 it is by the discharge of these ions and the consequent 

 reduction of the metal that kathode and Becquerel rays 

 are able to colour the glasses. 



Curves were constructed to show how the calcu- 

 lated absorptions and reflections of red, yellow, 

 green, and blue light by gold and silver films vary 

 with the volume proportion, jm, of metal in the film ; 

 and a comparison of these calculated colour changes with 

 those exhibited by the gold and silver films, which Faraday 

 and Beilby had prepared, when subjected to heat and to 

 pressure, indicated that (a) the films as first prepared 

 were in the ainorphous or granular phase ; (b) heating 

 diminished the density of the film, while pressure was able 

 to increase that density again ; and finally (c) this diminu- 

 tion of density was probably effected by the passage of 

 the metal from the amorphous to the granular phase, and 

 by the growth of the larger granules at the expense of the- 

 smaller, while increase of density was accomplished by 

 changing some of the metal from the granular to the 

 amorphous phase. 



Optical and other evidence ltd to the conclusion that 

 Carey Lea's silver was not allotropic, but consisted of 

 normal silver in a finely divided (but not necessarily- 

 granular) state. It appeared, therefore, probable that 

 manv forms of metals, which have hitherto been supposed 

 to be allotropic because they possessed optical properties 

 distinct from those belonging to the metals in their normal 

 states, were merely cases of fine division. Thus the 

 properties of Bolley's lead, of .Schiitzenberger's silver, and 

 of other alleged cases of allotropy cited by Roberts-Austen 

 (" Metallurgy," p. 90), do not require the postulation of 

 an allotropic molecule for their explanation. 



Faraday Society, July 3. — Mr. W. R. Cooper in the 

 chair. — .Some notes on the rapid electro-deposition of 

 copper : Sherard Cowrper-Coles. The Vtirious processes 

 for increasing the current densities in copper deposition 

 by using mechanical means for keeping the copper smooth 

 are classified as follows : — (i) revolving or moving the 

 kathode: (2) burnishing the copper during electro- 

 deposition ; (3) insulating the growths on the copper so as 

 to prevent further increase ; (4) rapid circulation of the 

 electrolvte ; (5) revolving mandrel at a critical speed (centri- 

 fugal process). — The use of balanced electrodes : \V. W. 

 Haldane Gee. — The electrolytic oxidation of hydro- 

 carbons of the benzene series, part ii., ethyl benzene, 

 cumene and cymene : H. D. Law and Dr. V. Mollwo 

 Perkin. — The electrolytic analysis of antimony : H. D. 

 Law and Dr. F. Mollwo Perkin. — Notes on heat insula- 

 tion, fKirticularly w-ith regard to materials used in furnace 

 construction : R. S. Hutton and J. R. Beard. — Storage 

 batteries and their electrolytes : R. W. Vicarey. — 

 .Mternale current electrolysis ; Prof. E. Wilson. — The two 

 last papers were taken as read, and the discussions post- 

 poned until the autumn. 



DlTKLlN. 



Royal Irish Academy, June 26.— Prof. R. Atkinson, 

 president, in the chair. — Prof. Ronald Ross gave an 

 account of the researches w-hich resolved the malaria 

 problem, and took occasion to refer to the interesting 

 mathematical problems connected with the diffusion of 

 mosquitoes. 



Paris. 



Academy of Sciences, July 31. — M. H. Poincare in the 

 chair. — The study of refraction at all heights. Formula? re- 

 lating to the determination of the coordinates of the stars : 

 M. Loeiwy. .-^ development of a system of formulae allow- 

 ing of the deduction of the positions of two pairs of stars 

 according to the new method given in the Comptes rendus 

 for July 17. Three tables of solutions accompany the 

 paper. — On an endoglobular h.-ematozoa found in the 

 jerboa : M. Laveran. The parasite is described and 

 classified as Haemogregarina Balfouri. — On a secondary 

 reaction of the halogen organo-magnesium compounds : 

 Paul Sabatier and A. IMaiihe. The cause of the low 

 yield sometimes observed in the reaction between a ketone 



