526 Intelligence and Miscellaneous Articles. 



The values for Jc, the diffusivity, given in square centimetres per 

 day, are as follows : — 



k. 



Gold in lead 3-19 at 500°. 



,, bismuth .... 4*52 „ 



„ tin 4-65 „ 



Silver in tin 4-14 „ 



Lead in tin 3*18 „ 



Rhodium in lead .... 3*04 „ 



Platinum in lead 1-69 at 490°. 



Gold in lead 3'03 „ 



Gold in mercury .... 0*71 at 11°. 



In order to afford a term of comparison, it may be stated that 

 the diffusivity of chloride of sodium in water at 18° is 1'04. 



The author at present refrains from drawing any conclusion as 

 to the evidence which the results afford respecting the molecular 

 constitution of metals. It is, however, evident that they will be 

 of value in this connexion, because, with the exception of the 

 gases, they present the simplest possible case of diffusion which 

 can occur — the diffusion of one element into another. 



Thus the relatively slow rate of diffusion of platinum as com- 

 pared with gold points to its having a more complex molecule 

 than the latter. 



Part II. — Diffusion of Solid Metals. 



The second part of the paper is devoted to the consideration of 

 the diffusion of solid metals. Much of the evidence is historical, 

 for there has long been a prevalent belief that diffusion can take 

 place in solids, and the practice in conducting important industrial 

 operations supports this view. In this connexion the author cites 

 two truly venerable " cementation ; ' processes. The object in the 

 first of these is the removal of silver from a solid gold-silver alloy, 

 while the second is employed in steel-making by the carburization 

 of solid iron. In both of these processes, however, a gas may 

 intervene, though the carburization of iron by the diamond, which 

 had been effected in vacuo by the author, suggests that if a gas 

 does iutervene in the latter case, its quantity must be very minute. 

 In connexion with the mobility of various elements in iron the 

 work of Colson, of Osmond, and of Moissan is specially referred to. 



The author points out that in 1820 Faraday and Stodart showed 

 that platinum will alloy with steel at a temperature at which even 

 the steel is not melted, and they express their interest in the 

 formation of alloys by cementation, that is by the union of solid 

 metals. 



The remarkable view expressed by Graham, in 1863, that the 

 " three conditions of matter (liquid, solid, and gaseous) probably 

 always exist in every liquid or solid substance, but that one pre- 

 dominates over the other.," is shown to have afforded ground for 



