( 766 ) 
a 1 doa tu ; arr 
pa == on I( di jk I; od io? stg) eng He (11) 
must be determined for each value of fo. 
After determining (pv), it is necessary to reduce it from its 
value at f to that of the required isotherm /, not much removed 
from it, this reduction is only possible when approximate values of 
the change in (pva)t, due to temperature are known. 
If we put 7; — ts — t we have 
(p04 oS pea) (A ude es eee 
1 / dv 
= = (7(44)| (a eee 
EREN i ar nay ae Sn 
for the reduction at constant pressure, and correspondingly 
(ro = Goal yy) Ere et EN 
1 „dp 
here ui = n= (4) ess Al 
Ww tage. Gy, Ti 5 zi an Ti ( ) 
for the reduction at constant volume, and thus to another pressure. 
S 9. The constants necessary for the caleulations. 
A = 15,9467 em. after Comm. no. 60. 
k was assumed at the ordinary temperature to be equal to 0,000024 
as for the kind of glass used it cannot differ much from that of 
Jena glass. 
The values of a and a, are calculated for each gas from the 
series of Comm N°. 70 when no better data are at hand. 
In the calibrations of graduated tubes and determinations of the 
volumes V and U no very special precautions where taken beyond 
those ordinarily employed in accurate calibration. U) was determined 
by treating the piezometer as a barometer, pumping free of gas and 
filling in vacuum, it was then placed in ice. U, was calibrated 
by a mercury thread. U3 can be directly determined by screwing 
the end g, of the steel capillary onto the end of b; and providing 
the other end of the capillary with a steel connecting tube carrying 
a glass cock. By connecting by to the air pump the whole can be 
then well evacuated and the mercury slowly admitted through the 
above mentioned cock, until it reaches above the top divisions of 
the tube b4. When dry air has been admitted the tube is placed 
vertically and the steel connecting tube carefully removed. By 
adjustment the mercury is brought just to the end of the capillary 
and its position in the tube 4, read by a cathetometer, the temperature 
being also observed. To cl.eck these determinations the volume is 
calibrated in parts, the steel capillary after the method of Comm. 
N°, 60 and the glass either by a mercury thread or by screwing 
