BIOGRAPHICAL MEMOIR OF JOSEPH HENRY. 165 



given off, four ounces of water were placed in a platinnm crucible and 

 supported on a ring -stand over a Hame of hydrogen; tlie minutes and 

 seconds of time were then accurately noted which were required for the 

 raising of the water from the temperature of G0<=> to the boiling point. 

 The same experiment was repeated with an equal quantity of water, 

 with the same flame, into which a piece of mica was inserted by a handle 

 made of a narrow slip of the same substance. With this arrangement 

 the light of the flame was much increased, while the time of bringing 

 the water to the boiling point was also commensurately increased, thus 

 conclusively showing that the increase of light was at the expense of the 

 diminution of the temperature. These experiments were instituted in 

 order to examine the nature of the fact mentioned by Count Eumford, 

 that balls of clay introduced into a fire under some conditions increase 

 the heat given oft' into an apartment. From the results just mentioned 

 it follows that the increase in the radiant heat, which would facilitate 

 the roasting of an article before the fire, would be at the expense of the 

 boiliug of a liquid in a vessel suspended directly over the point of com- 

 bustion. 



XIII. Another investigation had its origin in the accidental observa- 

 tion of the following fact : A quantity of mercury had been left undis- 

 turbed in a shallow saucer, with one end of a piece of lead wire, about 

 the diameter of a goose-quill, and six inches long, plunged into it, the 

 other end resting on the shelf. In this condition it was found, after a 

 few days, that the mercury had passed through the solid lead, as if it 

 were a'siphon, and was lying on the shelf still in a liquid condition. 

 The saucer contained a series of minute crystals of an amalgam of lead 

 and mercury. A similar result was produced when a piece of the same 

 lead wire was coated with varnish, the mercury being transmitted with- 

 out disturbing the outer surface. 



Wlien a length of wire of five feet was supported vertically, with its 

 lower end immersed in a vessel of mercury, the liquid metal was found 

 to ascend, in the course of a few days, to a height of three feet. 

 These results led me to think that the same property might be possessed 

 by other metals in relation to each other. The fii'st attempt to verify 

 tins conjecture was made by placing a small globule of gold on a plate of 

 sheet-iron and submitting it to the heat of an assaying furnace, but the 

 experiment was unsuccessful, for, although the gold was heated much 

 beyond its melting point, it showed no sigus of sinking into the pores 

 of the iron. The idea afterward suggested itself that a difi'erent result 

 would have been obtained had the two metals been made to adhere to 

 each other, so that no oxide could form between the two surfiices. To 

 verify this a inece of copper, thickly plated with silver, was heated to 

 near the melting point of the metals, when the silver disappeared, and, 

 after the surface was cleaned with diluted sulphnric acid, it presented a 

 uniform surface of copper. This plate was next immersed for a few 

 minutes in a solution of muriate of zinc, by which the siu-face of copper 

 was removed and the surface of silver again exposed. The fact had 

 long been observed by workmen in silver-plating that, in soldering the 

 parts of plated metal, if care be not taken not to heat them unduly, the 

 silver will disappear. This eflect was supposed to be produced by evap- 

 oration, or the burning off, as it was called, of the platiiig. It is not 

 improbable that a slow diffusion of one metal into the other takes place 

 in the case of an alloy. Silver coins slightly alloyed with copjior, after 

 having lain long in the earth, are found covered with a salt of copper. 

 This may be explained by supposing that the alloy of copper at the sur- 

 face of the. coin enters into combination with the carbonic acid of the 



