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difference of tension of 0.001 mm. Hg., Mr. Drererror takes as 
limit of his accuracy 0,001 mm. Hg. Therefore he states clearly, 
that he draws only qualitative conclusions. [ am, however, convin- 
ced, that the difference in temperature in my bulbs, which have 
a volume of 100 eem, is less than 0,0025°, which also appears 
from the fact that when I read the manometer, when comparing 
water with water, the manometer indicated accurately to 0,1 mm. 
the same difference of position, as when there was communication 
between the two sides of the manometer, and the bulbs were closed. 
As a deviation of the manometer of 0,1 mm. agrees with —+ 0,00025 
mm. Hg, the difference of temperature of the two bulbs must be 
exceedingly small. 
Some time ago prof. JAHN at Berlin wrote to me to ask, whether 
I was sure, that my solution had been perfectly free from air and 
if I would repeat some of my experiments once more, after having 
first reduced the solutions in vacuum to half of its original volume 
by means of evaporation. 
First I tried to comply with Prof. Jatn’s wish in the following way. 
The bulbs with water and solution were successively shut off from 
the apparatus by turning a tap and the air was exhausted by means 
of a velocity pump, while they were heated softly. During this the 
tube, connecting the bulb with the apparatus, was moistened with 
condensed vapour of water. Threugh the rise of the temperature 
the grease with which the tap (by means of which the communi- 
eation of the bulb with the apparatus was broken off or restored), 
was greased, spread over the inside wall of the tube, and this is 
the reason why I could not make use of this way of boiling. It 
seems namely, that the vapour tension of a layer of water on the 
greased part of the tube is so small, that the water was not distilled 
into the bulb, though the bulb was cooled to 0° and the temperature 
of the room was + 20°. I was therefore obliged to apply another 
method, by which rise of temperature was excluded. The most 
practical method appeared to be the following. 
When at the ordinary temperature most of the air was exhausted 
from the bulbs with water and solution by means of the velocity- 
pump, all the remaining air was expelled by bringing about the 
communication of the bulbs with the apparatus, after first having 
closed the bulbs for drying. The communication between the bulbs 
and the apparatus was interrupted after some moments, and when 
the vapour of water had been absorbed by the drying bulbs, the 
