( 470 ) 
method. It seemed to me there would be no particular difficulty in 
comparing the vapour tensions of pure water and solutions at a 
temperature different from 0°. I tried to gain my object by deter- 
mining the difference in pressure required to equalise the boiling 
points of pure water and saline solutions. 
In an article entitled: ,An apparatus to keep the vapour tension 
of a boiling liquid ens 1) the apparatus is described which I 
will briefly call ,manostat’”. This manostat enables me to reduce 
the pressure in a certain space to any desired extent, within definite 
limits, and then to keep it constant within 0.5 m.m. of water. By 
regulating the pressure of this apparatus it is therefore possible to 
make all solutions show the same boiling point. To be able to accu- 
rately read off the diminution in pressure, pure water is boiled under 
the same condition as the solution and from its decrease in temper- 
ature may be calculated the decrease in pressure corresponding with 
the decrease in vapour tension of the solution. 
Preliminary Experiments. 
I experienced great difficulties in my preliminary work when 
using the apparatus of BeckMANN?’). Firstly, because the indication 
of the thermometer was dependent on the degree of heating; this 
is chiefly due to the wrong manner in which the condensed solvent 
runs back into the boiling mass. 
Secondly, because the actual boiling vessel was not sufficiently 
screened to prevent radiation, which was shown by the fact, that 
mild air-currents had a perceptible influence on the indication of 
the thermometer. 
A third drawback experienced in my preliminary trials, but which 
was not caused by any defect in BECKMANN’s apparatus was as follows: 
The indication of the thermometer appeared to be dependent on 
the place occupied by the mercury reservoir in the column of liquid. 
As far as I am aware, nobody has, as yet, called attention to this 
fact but as will be shown presently, it is a factor which under 
special circumstances is to be reckoned with. On account of this, a 
number of published results are undoubtedly faulty. 
It is plain that this phenomenon may be accounted for by the 
difference in pressure between the different layers of liquid, but 
that it should be noticed so decidedly in boiling water or in boiling 
1) Verslag Kon. Acad. Noy. 27 1897. 
*) Zeitschr. f. physik. Chem, 1891. 
