( 777 +) 
§ 16. Measurements with Hydrogen. The piezometer used was 
the same as that given in Comm. No. 78> 0? Series V, the only dif- 
ference being that the capillary volume is here somewhat larger. 
The hydrogen was prepared in the manner described in Comms. 
N° 29 and N° 60, and the piezometer filled in the same way as 
for oxygen. 
The measurements were also carried out in precisely the same way 
as described above for oxygen. After the measurements given here 
were finished we had intended to proceed directly to low tempera- 
tures, but during the insertion of the piezometer into the cryo- 
state the steel capillary was broken so that these measurements 
had be postponed and moreover we were unable to redetermine the 
normal volume after the measurements. Fortunately the measurements 
at 0°.0 C. were included between two sets at 20°.0 C. which agreed 
well among themselves, so that we could be reasonably certain that 
no leakage had occurred. 
For at the calculation of the normal volume we have used 
Er ee 170 
GN = le | — 0,00366 
to dt 7 ODS HOP jp == 
and for the measurements at higher pressure 
li d 200 
ge. I( =) | — 0,00357 
P 
a —— 
4 Vo dt 0°.0, for p = 40 
The measurements of the normal volume gave 
TABLE XV. Normal volume Hs} Series IL. 
Mean Diff. 
Series ZZ. N° 1 + 0.24 
582.74 
0) 
and the measurements at higher pressure the following values. The 
measurements at 20°.0 C. are directly compared with those of 
ScHALKWIJK (loc. cit.) at the same temperature calculated by means 
of a slightly improved equation to the one given before 
pva = 1.07258 + 0.000667 d + 0.00000099 d 
where d is expressed in terms of the normal volumes, 
