Bakerian Lecture: On the Diffusion of Metals

W. C. Roberts-Austen
1896 Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences  
A lloys fo rm ed b y D iffusion. R o b e rts-A u ste n , W . C. P h il. T ra n s . A 1896, vol. 187, pp. 383-115. D iffusion of M etals, S o lid a n d Liquid*, C o n s ta n ts of. R o b e rts-A u ste n , W . O. P h il. T ran s. A 1896, vol. 187, pp. 383-415. G old, D iffu siv ity of, in L ead , &c. R o b e rts -A u s te n , W. C. P h il. T ran s. A 1896, vol. 187, pp. 383-415. L ead , D iffu siv ity of M e tals in L iq u id a n d S olid. R o b e rts-A u sten , W . C. P h il, T ran s. A 1896,
more » ... T ran s. A 1896, vol. 187, pp. 383-415. M e tals, F lu id a n d S olid, D iffusion of, R o b e rts-A u ste n , W . C. P h il. T ran s. A 1896, vol. 187, p p. 383-415. M olecu lar M o v em en t in L iq u id a n d S olid M e tals. R o b e rts-A u ste n , W . C. P h il. T ran s. A 1896, vol. 187, pp. 383-415. O sm otic P re ssu re in L iq u id M e tals a n d Solid M etals. R o b e rts-A u ste n , W . C. P h il. T ran s. G old, Pl a t in u m , a n d R h o d iu m , d if f u sin g in Molten L ea d a n d in M olten B ism u th . The diffusion o f m olten and solid m etals has long dem anded investigation , their molecular m ob ility b eing o f great in terest in relation to th e constitution o f matter, and its resu lts o f m uch industrial im portance. * H eycock and N e v il l e , ' Trans. Chem. the gold and copper was roughly effected. The molecular mobility of the metals has influenced the result, and the metals dissolved in each other, become, by a spontaneous process, spread or diffused uniformly; in this case the uniformity is not materially disturbed when the solidification of the mass is effected. In view of the great interest connected with such action, the" absence of direct experiments is remarkable, but this may perhaps be explained by the difficulty of conducting them. The sources of these difficulties are many. Such metals as are suitable for study require a more or less elevated temperature to melt them, and, where diffusion is concerned, small variations in temperature may be of much import ance, for, as G r a h a m showed, the rate of diffusion of salts in water is greatly increased by a small rise in temperature, the diffusibility of chloride of sodium, for instance, being more than doubled by a rise of 33°. I t is now well-known that the osmotic pressure of a salt in solution is measured by the diffusion which takes place. A rise of temperature, therefore, which augments the osmotic pressure, must also increase the rate of diffusion. G r a h a m further pointed out that the inequality of diffusion which various saline substances exhibit at a low temperature, becomes less at a high temperature, and he therefore concluded that " it would appear to be the effect of a high temperature to assimilate diffusibilities " of different salts.* In the case of molten metals, the necessity for working at high temperatures, which until quite recently could not be readily measured even with approximate accuracy, and the fear that the value of the results would be impaired by the action of convec tion currents, must have deterred physicists from undertaking experiments on the diffusion of molten metals. O stw a l d 's statement + with reference to the diffusion of salts, that " to make accurate experiments on diffusion is one of the most difficult problems m practical physics," may well have given rise to doubts whether my* method which seemed to be available for conducting such investigations with molten metals would afford trustworthy results/ The difficulties are obvious, but my long , , connection with G r a h a m 's researches made it almost a duty to attempt to extend his work on liquid .diffusion to metals, and, therefore, fourteen years ago the present investigation was undertaken, but it was abandoned because I was unable to measure" with sufficient accuracy the temperature at which diffusion took place, and it has only been resumed during the past two years. As regards the history of the subject, I believe that a brief communication of my own on the mobility of gold and silver in molten lead," to the Chemical Section of the British Association at the meeting at Southport in September, 1883, embodied the : results of the first experiments which were ever made with the direct object of investigating the diffusion of molten metals and alloys, other than those of mercury which are fluid at the ordinary temperature.
doi:10.1098/rsta.1896.0010 fatcat:n7a5d5wzzbhsvgm4nmtjy75gf4