170 
Dll. .M. W. TIIAYEES, YR. G. .SENDER, AND DR, A. .lAQUEROD 
Appendix I.— 0)i the Melting-Point of Hydrogen. 
Dewar (‘ Doy. Soc. Proc.,’ 1891, vol. G8, p. 360) states that the melting-point ot 
hydrogen on the helium scale is 16°. The method Iw wliich the measurement was 
made luis not been recorded ; lie had previously given the melting pressure as 
55 mdlims, (see ]>. 106). Our experiments of the vapour pressures of hydrogen 
appeared to indicate that the melting-point lay eonsiderahly 
lielow the temperature given hy Dewar, for not only did 
the numerical results hear evidence that at temjDeratures close 
to 14° we were still dealing with liquid, hut when after main¬ 
taining a pressure of 55 millims. in the apparatus for some time 
the Amcuum vessel was found to contain liquid only. We 
therefore decided to carry out a separate experiment with a view 
to determining the exact melting-point. 
The apparatus employed in this experiment is .shown in fig. 2. 
The tube a, which was 6 millims. in diameter, and 150 millims. 
long below tlie side tube h, passed through the rubber stopper p 
of the apparatus shown in fig. 1, so that the lower end of it la}" 
at the level of the middle of the thermometer ludb. The tube a 
contained a very thin glass rod, c, bent at its lower end into a 
hook, and joined at the top to a piece of soft iron wire wound 
into a solid spiral, d. Round the tube a above the side tube 
a coil of insulated wire was wound forming a solenoid ; by 
passing a current through the coil, the rod c with its iron head 
d could he given a vertical motion of about 3 millims. 
The side tube h communicated with a mercury reservoir con¬ 
taining pure hydrogen from palladium, with a manometer of 
the type described in Part II. (fig. 2), and through a stop¬ 
cock with the mercury jmmp. 
In carrying out the experiment the lower j^art of the tube a and the thermometer 
bulb were cooled in licjuid hydrogen boiling under reduced pressure in the manner 
described on p. 160, and about 100 cub. centims. of gaseous hydrogen was allowed to 
enter and liquefy in it. At all temperatures down to 14°'2, which corresponded to the 
lowest pressure which we were able to obtain under the conditions of the experiment, 
the hydrogen appeared to remain liquid, for, on passing the current through the 
solenoid, the piece of iron d was seen to move iq^wards. 
Maintaining the temperature outside a at from 14°‘2 to 14°‘8, the stop-cock 
connecting the side tube h with the mercury pump was opened for a moment. The 
]n’ossure in the ajiparatus immediately fell to 49 millims., and remained steady there 
