NATURAL PHILOSOPHY. 183 



palladium did not increase, but fell slightly at the same time, 

 namely, from 12.38 to 12.12; proving that this contraction of the 

 wire is in lengtli only. The result is the converse of extension 

 by wire-drawing. The retraction of the wire is possibly due to 

 an effect of wire-drawing, in leaving the particles of metal in a 

 state of unequal tension, a tension which is excessive in the di- 

 rection of the length of the wire. The metallic particles would 

 seem to become mobile, and to right themselves in proportion as 

 the hydrogen escapes ; and the wire contracts in length, exptmd- 

 ing, as appears by its final density, in other directions at the same 

 time. 



A wire so charged with hydrogen, if rubbed with the powder 

 of magnesia (to make the flame luminous), burns like a waxed 

 thread when ignited in the flame of a lamp. 



Numerous other experiments were also performed, with re- 

 markable unanimity of result ; the specific density of hydrogeni- 

 um being found by calculation from several successive experi- 

 ments to be, respectively, 1.708, 1.898, 1.977, 1.017, 1.927, 1.930, 

 2.055, the variations resulting from difi'erent volumes being used 

 in the alloy, the highest densities being obtained when small 

 quantities were used. 



In these experiments the hydrogen was expelled by exposing 

 the palladium placed within a glass tube to a moderate heat short 

 of redness, and exhausting by means of a Sprengel tube ; but 

 the gas was also withdrawn in another way, namely, by making 

 the wire the positive electrode, and thereby evolving oxygen 

 upon its surface. In such circumstances, a slight film of oxide 

 of palladium is formed on the wire, but it appears not to interfere 

 with tlie extraction and oxidation of the hydrogen. The wire 

 measured : — 



DiflPerence. 



Before charge, 443.25 m.m. 



With hydrogen, 449.90 " 6.G5 m.m. 



After discharge, 437.31 " 6.94 " 



The retraction of the wire, therefore, does not require the con- 

 currence of a high temperature. Tliis experiment further proved 

 that a large charge of hydrogen may be removed in a complete 

 manner, b}'' exposure to the positive pole — for 4 hours in this 

 case ; for the wire in its ultimate state gave no hydrogen on being 

 heated in vacuo. 



Experiments were also made to determine the conducting 

 power of the palladium and hydrogenium wire, and its magnetic 

 properties, the details of which may be hereafter referred to. 

 The record of these experiments, as communicated to the Royal 

 Society, January 14, by Mr. Graham, forms one of the most im- 

 portant contributions to science that has been recently made, and 

 Mill immediately arrest the attention of the entire scientific 

 world. 



Lxj 



