168 MR JAMES DEWAR ON THE 
process of taking specific gravities because of the continual evolution of gas 
preventing exact weighings being taken in water. 
In the experiments to be detailed a cubical mass of the metal was charged 
with hydrogen by electrolysis, taken at different times during the progress of 
the saturation, and weighed in air and in water. If the mass was allowed free 
exposure to the air for several hours little difficulty arose from the evolution of 
gas when immersed in water, and accurate results could be obtained. 
From the experimental numbers the specific gravity of the absorbed 
hydrogen was calculated by the well-known formula— 
when w, and w, are the weights of the substance, S, and S, the specific gravities, 
and S the mean specific gravity found by experiment. This formula assumes 
that no condensation takes place in the palladium. 
TABLE J.—Sprciric GRAVITY OF BAR PALLADIUM AT DIFFERENT TIMES DURING 
SATURATION WITH HYDROGEN. WEIGHT OF ORIGINAL PALLADIUM, 31°'802. 



Weight of Weight of : ; 
: Palladium and | Palladium and |Specific gravity Specific gravity Weight of 
Experiments. | Hydrogen in | Hydrogen in | of substance. | °f Hydrogen | pydrogen. 
air. water. (calculated). 
1 31°8748 29°1150 11°5488 0°6215 0°0728 
2 31°9230 29°0860 11°2520 0°6230 0:1210 
3 31°9425 29°0715 111259 0°6150 0:1405 
+ SL-9715 29°0615 10°9867 0°6081 0°1625 
5 31°9860 29°0500 10°8944 0°6270 0°1840 
6 31°9955 29°0455 10°8459 06299 0°1935 
i 32°0040 29°0450 10°8158 0°6388 0°2020 
8 (after ; ’ 2 
some days) 31°9940 29°0325 10°8033 0°6024 0°1920 



When the calculated values of the specific gravity of the hydrogen in the 
eight determinations of Table I. are examined it will be observed no material 
alteration can be said to take place in the specific gravity during the course of 
the saturation, regard being paid to the difficulty of getting accurate weighings 
immediately after removal from the electrolytic cell. All the above determina- 
tions were made as quickly as possible after the palladium was taken from the 
pole of the battery. The mean of the results gives a specific gravity of 0°620 
for the hydrogen. The atomic volume of this condition of hydrogen is therefore 

