172 ; MR JAMES DEWAR ON THE 
TABLE III.—Speciric HEAT. EXPERIMENTS WITH PALLADIUM PLATE. THREE DIFFERENT 
HyprIDES. WEIGHT oF PLATE, 37°848 GRAMMES. EQUIVALENT OF WATER AND CALORIMETER, 
107 GRAMMES. 








A Te 1601 IV. 
Weight of Hydrogen in Palladium, 0-210 0-129 0-0512 Nothing. 
2°891 2°694 2°368 AV 
Rise in Calorimeter for a fall of 2°870 2°657 2°362 2°100 
LOO AC, : é : 2°856 2646 2-300 2-082 
9°858 2°659 2°402 2°086 
Mean rise, : : : 2°869 2664 BAT 2:096* 
Rise due to Hydrogen, . : 0-773 0°568 0°281 
Specific heat of Hydrogen, : . 8°930 4-70 5°88 
Weight of Hydrogm in «Huge Caloringer —Spgsfe Heat fom agen 
I. in excess of II. 0-081 I, and II. 0:205 ieeand all, 2°70 
II. in excess of III. 0°0778 iivand Th. 0287 Li angelic 633949 oro 
I. in excess of III. 0°1588 I. and III. 0°492 and ik S30 
Coefficient of Expansion. 
As the observations on the coefficient of expansion had to be made with the 
same pieces of palladium used in the former experiments, the only method that 
could be employed was to weigh the hydride in distilled water of different tem- 
peratures, as MATHIESSEN did in his well-known paper on the expansion of metals 
and alloys (“ Phil. Trans.,” 1866), and to deduce the mean cubical expansion 
from the difference of weights and the known density of water. Experiments 
made in this way require great care in execution, and when every precaution is 
taken, are yet liable to considerable variation. Any difference of temperature 
in different portions of the water in which the alloy is weighed at the time of the 
observation, causing currents in the fluid, or the condensation of moisture on 
the fine platinum wire used to suspend the substance, renders the results useless. 
But in this case the difficulties are greatly increased from the minute bubbles 
of hydrogen that are apt to accumulate at any angular point of the mass, and 
must be removed by suddenly depressing or lifting the mass. After making a 
great many observations in this way, it became clear that the method would 
not yield results of very great accuracy when applied to the case of palladium 
containing hydrogen; in the meantime, the results obtained are provisionally 
stated. Generally a mass of palladium containing hydrogen nearly equivalent to 
* Mean for six experiments. 

