1896.] 



Presents. 



285 



maintained at a temperature of 251° (which is 75° below the melting 

 point of lead) for thirty-one days. At the end of this period the 

 solid lead was cut into sections, and the amount of gold which had 

 diffused into each of them was determined in the usual way. Other 

 experiments follow, in which the lead was maintained at 200°, and at 

 various lower temperatures down to that of the laboratory. The 

 following are the results : — 



k. 



Diffusivity of gold 



in fluid lead at 550° . . . 



. 319 



5» 



solid 



55 



251° . . . 



. 003 



?> 



}? 



55 



200° ... 



. 0-007 



»> 



J5 



55 



165° ... 



. 0-004 



J> 



55 



55 



100° . . . 



. 0-00002 



The experiments at the ordinary temperature are still in progress, 

 but there is evidence that slow diffusion of gold in lead occurs at the 

 •ordinary temperature. The author points out that if clean surfaces 

 of lead and gold are held together in vacuo at a temperature of only 

 40° for four days, they will unite firmly, and can only be separated 

 by the application of a load equal to one-third of the breaking strain 

 of lead itself. 



The author thinks it will be considered remarkable that gold placed 

 at the bottom of a cylinder of lead, 70 mm. long (which is to all 

 appearance solid), will have diffused to the top in notable quantities 

 at the end of three days. He points out that at 100° the diffusivity 

 of gold in solid lead can readily be measured, though its diffusivity 

 is only 1/100,000 of that in fluid lead at a temperature of 500°. He 

 also states that experiments which are still in progress show that the 

 diffusivity of solid gold in solid silver, or copper, at 800° is of the 

 same order as that of gold in solid lead at 100°. 



He concludes by warmly thanking Mr. A. Stansfield, B.Sc, who 

 assisted him in all but the earlier portion of the work, and by ex- 

 pressing the hope that the experiments described in the paper will 

 show that the diffusion can readily be measured in solid metals, and 

 that they will cai*ry one step further the work of Graham. 



Presents, February 20, 1896. 



Transactions. 



Brighton : — Brighton and Sussex Natural History and Philosophi- 

 cal Society. Abstracts of Papers together with Annual 

 Report. 1895. 8vo. Brighton ; Catalogue of Books in the 

 Library. 8vo. Brighton 1895. The Society 



.Liege : — Societe Geologique de Belgique. Annales. Tome XVIII • 

 Livr 1. 8vo. Liege 1891. The Society 



