336 



Mr. J. Dewar on the Physical 



where w l and w 2 are the weights of the substance, Sj and S 2 the 

 specific gravities, and S the mean specific gravity found by expe- 

 riment. This formula assumes that no condensation takes place 

 in the palladium. 



Table I. — Specific Gravity of Bar Palladium at different times 

 during Saturation with Hydrogen. Weight of original Pal- 

 ladium 31-802. 





Weight of 



Weight of 



Specific 

 gravity of 

 substance. 



Specific 





Experi- 



palladium and 



palladium and 



gravity of 



Weight of 



ments. 



hydrogen in 



hydrogen in 



hydrogen 



hydrogen. 





air. 



water. 





(calculated). 





1. 



31-8748 



291150 



11-5488 



0-6215 



00728 



2. 



31-9230 



290860 



112520 



0-6230 



01210 



3. 



31-9425 



290715 



11 1259 



0-6150 



01 405 



4. 



31-9715 



290615 



10-9867 



6081 



1625 



5. 



31-9860 



29 0500 



10-8944 



06270 



1840 



6. 



31-9955 



29-0455 



10-8459 



0-6299 



01935 



7. 

 8 

 (after some 



320040 



290450 



10-8158 



0-6388 



0-2020 



I 31-9940 



29 0325 



10-8033 



0-6024 



01920 



days). 



J 











When the calculated values of the specific gravity of the hy- 

 drogen 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 imme- 

 diately after removal from the electrolytic cell. All the above 

 determinations were made as quickly as possible after the palla- 

 dium 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 1*6; 

 and the alteration of volume is equivalent to saying that, in the 

 formation of this condition, 7 litres of gas are condensed into 1 

 cubic centimetre. The maximum charge of hydrogen the palla- 

 dium would take was given to No. 7 experiment ; and this very 

 nearly accords with the composition Pd 3 H 2 . In treating masses 

 of palladium the above proportion was never exceeded. 



As all the above experiments were made with bar palladium 

 increasing to saturation, it was necessary to find similar values 

 for a mass decreasing from saturation, the hydrogen being ex- 

 pelled by heating. For this purpose a piece of plate palladium 

 was employed. When the plate was fully charged for the first 

 time, and the specific gravity of the hydrogen found as in the 

 previous experiment, the result was a density of 0*621: the plate 

 in this case contained 0*21 grm. of hydrogen. When a por- 

 tion of the hydrogen was expelled by heat, leaving 0*127 grm. 



