1900.] on Solid Hydrogen. 479 



carbons separate, and consequently the flame C is less luminous 

 than B. The liquid air bath condensi s the ethylene and a large 

 part of the marsh gas, and allows the carbonic oxide and the hydrogen 

 to pass through so that flame D is less luminous than 0. Finally, 

 afrer the liquid hydrogen bath, nothing escapes condensation but free 

 hydrogen, the carbonic oxide and any marsh gas being solidified ; 

 the result is, the flame E is almost invisible. 



A really practical application of liquid hydrogen is the purification 

 of helium obtained from the gases emitted by the mineral springs of 

 Bath. Although the helium only amounts to one-thousandth part by 

 volume — the nine hundred and ninety-nine being chiefly nitrogen — yet 

 the low temperature method of separation can be successfully applied. 



Now that we know definitely the approximate values of some of the 

 more important physical constants of liquid hydrogen, it is interesting 

 to look back: at the values that have been deduced — say for such a 

 constant as the density — by various workers using entirely different 

 methods. The following table gives some of the more important 

 values of the density of hydrogen under the different conditions in 

 which it enters into organic and inorganic bodies. 



Density op Hydrogen in Different Conditions. 



Kopp . . . . Organic bodies • 1 8 



Amagat .. Limit of gaseous compression.. 0'12 



Wroblewski .. Van der Waals' equation . . .. 027 (critical density) 



Van der Wuals Superior limit of density .. .. 0"82 



Graham .. Palladium alloy 20 



Dewar .. .. Palladium alloy 063 



Dewar .. .. Liquid hydrogen at B.P - 07 



My density at the boiling-point agrees substantially with that 

 which can be deduced from Wroblewski's form of the Van der Waals' 

 equation. The deduced densities of Kopp for organic bodies and 

 Amagat for gaseous compression are both about the same value, and 

 may be taken as a mean to be twice the observed density of hydrogen 

 in the liquid state. The conclusions of Graham and myself, touch- 

 ing the density of the hydrogen in the so-called alloy of palladium, 

 must be regarded as altogether exceptional. Even my value would 

 exceed the density of the stuff constituting the real gas molecule, ac- 

 cording to the theory of Van der Waals. In order to harmonise the 

 palladium hydrogen results with those deduced from the study of 

 organic bodies, we must assume that, during the formation of the 

 so-called hydrogenium, a condensation of the palladium sufficient 

 to increase its density by one-fifth must take place. This is by 

 no means an unreasonable hypothesis. The mode of determining 

 the density of hydrogen at its melting-point has been previously 

 described and found to be 0*086. In the same way the approxi- 

 mate values for the densities of nitrogen and oxygen at their melting- 

 points have been found, their respective values being 1-07 and 1*27. 

 The following table shows the comparison between my results and 

 those given by Amagat for high gaseous compressions : — 



