228 WRITINGS OF JOSEPH HENRY. [1845 



ON THE CAPILLARITY OF METALS. 

 (Proceedings of the American Philosophical Society, vol. iv, page 176-178.) 



June 20, 1845. 



Professor Henry gave an account of some observations he 

 had made on capillarity, in addition to those he had before 

 communicated to the Society on the same subject. 



In 1839* he presented the results of some experiments on 

 the permeability of lead to mercury ; and subsequent observa- 

 tion had led him to believe that the same property was 

 possessed by other metals in reference to each other. His 

 first attempt to verify this conjecture was made with the 

 assistance of Dr. Patterson, at the United States Mint. For 

 this purpose a small globule of gold was placed on a plate 

 of sheet iron, and submitted to the heat of an assaying 

 furnace; but the experiment was unsuccessful; for although 

 the gold was heated much above melting point it exhibited 

 no signs of sinking into the pores of the iron. The idea 

 afterward suggested itself that a different result would have 

 been obtained had the two metals been made to adhere 

 previous to heating, so that no oxide could have been formed 

 between the surfaces. In accordance with this view he 

 inquired of Mr. Cornelius, of Philadelphia, if in the course 

 of his experience in working silver-plated copper in his 

 extensive manufactory of lamps he had ever observed the 

 silver to disappear from the copper when the metal was 

 heated. The answer was that the silver always disappears 

 when the plate is heated above a certain temperature, leaving 

 a surface of copper exposed ; and that it was generally believed 

 by the workmen that the silver evaporates at this tempera- 

 ture. 



Professor Henry suggested that the silver, instead of evap- 

 orating, merely sunk into the pores of the copper, and that 

 by carefully removing the surface of the latter, by the action 

 of an acid the silver would re-appear. To verify this by ex- 



*[Proc. Am. Phil. Soc. vol. i, p. 82. See ante^ page 140.] 



