On Surfusion in Metals and A Hoys. 447 



" On Surfusion in Metals and Alloys." By W. C. ROBERTS-AUSTEN, 

 C.B., D.C.L., F.R.S. Received May 20, Read May 26, 



1898. 



(PLATES 8, 9.) 



Introduction. 



The fact that metals and alloys may be maintained in a fluid state 

 at temperatures which are many degrees below their true freezing 

 points, has been but little studied. As regards salts the question of 

 surfusion has recently received much attention. Ostwald* has 

 shown, as the result of an investigation of great interest, that a very 

 minute quantity of a solid will cause a mass of the same substance to 

 pass from the surfused to the solid state. His work, moreover, has 

 led him to distinguish between the meta-stable, or ordinary condi- 

 tion in which surfusion takes place, and the labile condition which 

 occurs at temperatures much below the melting point. Ostwald's 

 paper, and one by M. Brillouin,f on the theory of complete and pasty 

 fusion lead me to offer the Royal Society the results of some experi- 

 ments of my own on the surfusion of metals. 



Historical. 



Metals do not appear to have been studied from the point of view 

 of surfusion until the year 1880, when some excellent experiments 

 on the surfusion of gold were made by the late Dr. A. D. van 

 Riemsdijk,]; by whose early death, which occurred last year, Holland 

 has lost a skilful physicist. He pointed out that : 



" Faraday, in his memoir on regelation, published in 1858, stated 

 that acetic acid, sulphur, phosphorus, many metals and many solu- 

 tions, may be cooled below the congealing temperature prior to solidifi- 

 cation of the first portions." On the other hand, in their treatises 

 on physics, Danguin|| and Jamin^f mention tin as the only metal 

 which is capable of remaining liquid at a temperature 2'5 below 

 the true melting point of the metal, which is 228 C. 



Van Riemsdijk's contribution to the subject of surf usion of metals 

 consisted in showing that the well-known phenomenon of eclair, the 

 brilliant flash of light which often attends the solidification of the 

 metal in the ordinary assay of gold, is really due to surfusion. He 



* ' Zeit. fur Physikal. Chem.,' 1897, vol. 22, p. 3. 



t 'Ann. de Chim. et de Phys.,' 1898, vol. 13, p. 264. 



'Ann. de Chim. et de Phys.,' 1880, vol. 20, p. 66. 



' Experimental Researches in Chemistry and Physics/ p. 379. 



|| Vol. 1, 1855, p. 892. 



1" Vol. 1, 1859, p. 105. 



