1896-97.] Prof. J. P. Kuenen on Ethane and Butane. 
435 
This copper cylinder is provided with two outlets, one at the 
top and the other starting near the bottom. Ethane may, there- 
fore, either be taken from the gas portion, or from the liquid 
portion of the condensed substance. The first sample was taken 
from the liquid, and will be called mixture a. The results 
obtained with this sample are contained in Tables III. -VI., XII., 
figs. 1 and 3. 
The apparatus employed was Ducretet’s apparatus, a tube with 
air being used as a manometer. The full description of apparatus 
and method of calculation will be found in former papers.* The 
only point to be noticed is the application of a little soft-iron 
stirrer inside the compression-tube, which is moved up and down 
by an electro-magnet outside the water-jacket which keeps the 
temperature constant. The pressures are measured in atmos- 
pheres, the volumes in an arbitrary unit, but in such a manner, 
that the volumes belong to equal original volumes (at 0° C. and 
1 atmosphere) for both mixtures. 
The substance' a behaved like a mixture, as regards both conden- 
sation and critical phenomena. The critical region, an expression 
which will be explained later on, ranged from 35’25 to 35 ‘7. 
A second sample was taken from the gas portion in the copper 
cylinder. This sample (mixture c) appeared to be accidentally 
almost identical with mixture a, the critical temperature being 
35*75, and the condensation-pressures at the beginning and at the 
end being only a little lower than for mixture a, e.g., p e = 32*78 
at 14*95, instead of 32*91. Xo further observations were made 
with this mixture. 
A third sample was again taken from the liquid. The results 
for this sample (mixture b) are found in Tables VII. -XI., XIII., 
and figures 2 and 3. 
The critical region for this gas lies between 38*35 and 39*25° C. 
The possibility of drawing from the cylinder samples of ethane 
differing so widely from each other in physical properties confirms 
the presence of a mixture in the cylinder. 
In order to get some idea as to the nature of the admixture, 
* Archives Neerlandaises , 26, pp. 354-422 ; Communications from the 
Physical Laboratory, Leiden, Xos. 4, 7, 8, 11, 13, 16, 17. Zeitschrift Physik. 
Chemie, 11, pp. 38-48, 
