1886.] on Properties common to Fluids and Solid Metals. 411 



rubbed liglitly on it the mercury will in 30 seconds penetrate the 

 mass, so that it breaks readily, although before the addition of the 

 mercury, the bar would bend double without any sign of fracture. 



With regard to the vaporisation of solid metals, time will only 

 permit me to remind you that Demar9ay * has shown that in vacuo 

 metals evaporate at much lower temiDcratures than they do at the 

 ordinary atmospheric pressure, and he suggests that even metals of 

 the platinum grouj) will be found to be volatile at comparatively low 

 temperatures. Merget f has shown that the solidification of mercury 

 by extreme cold does not prevent the solid metal evaporating into the 

 atmosphere surrounding it. 



With regard to the remaining properties on my list, you will say, 

 surely solids do not show any tendency to diffusion ? I have shown J 

 that in the case of molten metals the interdiffusion may be extremely 

 rapid, but, with regard to solid metals, some experiments conducted 

 by Sir Frederick Abel prove that carbon can pass from a plate of 

 richly carburised iron to one of iron free from carbon, against which 

 it is tightly pressed. This passage of carbon takes place at the 

 ordinary temperature, and it is difficult to exj^lain the transference of 

 matter without admitting the presence of some action closely allied 

 to the diffusion of liquids. 



Finally, can we offer any evidence of surface tension in solid 

 metals ? There is only one experiment to submit to you illustrating 

 a j)oint I am still investigating. Some months since Mr. F. W. 

 Fletcher, manager of the works of Messrs. C. Ash and Sons, the well- 

 known dealers in the precious metals, pointed out to me an interesting 

 property of a hard-drawn rod or thick wire of 13-carat gold ; the gold 

 being alloyed with silver and copper in the following proportions : — 



Gold 54-17 



Copper 33-33 



Silver 12-53 



100-00 



If such a rod be touched with a solution of chloride of iron or 

 certain other soluble chlorides, it will, in a short time, varying from 

 Sk few seconds to some minutes, break away, as is shown in the 



Fig. 14. 



A 



diagram, Fig. 14, the fracture rapidly extending for a distance of 

 some inches. 



[The image of the rod was projected on the screen, and in a few 



* ' Comptes Eendus,' xcv. p. 183 [1882]. 



t ' Ann. de Chim. et de Pbys.' [4], xxv. p. 121. 



X 'British Association Report/ 1883. p. 402. 



