A DEMONSTRATION EXPERIMENT ON THE DIFFUSION OF METALS EUGENE W.BLANX.241 N. 9TR STREET, ALLENTOWN; PENNSnVANI.4 This experiment, due to Joseph Henry (Director, Smithsoniau Institution, 1847-78) ( I ) , (2), is best described in his words. A lead tube of about half an inch in diameter and eight inches long happened to be left with one end immersed in a cup of mercury, and on inspection a few days afterwards it was observed that the mercury had disappeared from the cup, and was found on the floor a t the other end of the tube. Struck with the phenomenon, I again filled the cup with mercury; the next morning the same effect was exhibited. The mercury had again passed over through the tube, apparently like water through a capillary siphon, and was again found on the floor. By cutting the tube in pieces it was determined that the mercury had been transmitted through the walls of the tube and not through the hollow axis. The penetration takes place much more readily in the direction of the laminae of the metal than across them. Aplate of thicksheet lead was formed into a cup, and mercury poured into this; and it was found that before a drop had passed directly through, the mercury oozed out all around the edge of the plate. To perform the experiment take a lead rod about 6 inches long and a quarter of an inch in diameter and bend into the form of a siphon. Immerse the shorter leg in a small evaporating ARRANGEDNT oa A i dish filled with mercury and place a similar dish under the end of the longer leg to receive the ,,,s OP MERmercury which comes over. In five or six days all THE DIPPUSION cum THROUGH LEAD the mercury passes over leaving arborescent The mercury is cancrystals of an amalgam of lead in the upper evapo- tained in a test rating dish. The speed a t which the mercury tube and its weight quickens the time of passage comes over is much influenced by the texture of through the lead rod, the lead. The time required for the experiment can be greatly decreased by a modification of the above arrangement of apparatus. This modification is clearly shown in the accompanying figure and requires no comment. Literature Cited Proceedings Am. Phil. Soc.,1, 8 s (1S-39). ( I ) HENRY, Silliman's Am. J. Sci.,38, 18G1 (1839). ( 2 ) HENRY. +
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