3. The vapour tension determinations. The apparatus used by us 
for the vapour tension determinations, is represented in fig. 1. The 
manometer, which is fused 
into the tube A, differs from 
the one described in our 
previous communication only 
5 in this that it is more elon- 
c 8 gated and smaller; the length 
of the curved part amounts 
to three or four em., while 
the tube A has an external 
A diameter of 10 mm. and a 
length of 22 or 23 cm. The 
entire apparatus serving for 
the measurements has a length 
of about 28 em. after the 
Fig constriction at / has been 
melted off. On the outer tube A two marks have been made, so that the 
end of the needle is just between the two marks when the internal and 
external pressure is the same. The manometer can resist an excess of 
pressure of one atmosphere, and can therefore be evacuated ; then the 
end of the needle reaches the inner wall of A in some of the apparatus 
used by us. The sensitivity reached with this shape of apparatus 
varies between '/,, and '/,, atmosphere. 
Before the apparatus was filled the reservoir -C’ with the 
nitrogen tetroxide was cooled by means of a mixture of carbonic 
acid-aleohol, and evacuated by means of a GAEDE-pump through D. 
Then the constriction ) was melted off, and a quantity of nitrogen 
tetroxide was distilled over through the U-tube with phosphorus- 
pentoxide into B; for this purpose a cilindrical vessel was placed 
round the tube 4 by means of a cork, which vessel could be filled 
with alcohol cooled by carbonic acid. When a sufficient quantity of 
liquid was distilled over, the apparatus was separated from the filling 
apparatus by melting off at Z, after the nitrogen tetroxide in B and 
C had been brought to — 80°. 
We have applied two different methods for the determination of 
vapour tensions. 
a. For our first determinations we made use of the arrangement 
indicated in Fig. 2a. The apparatus AB was slid into a thiekwalled 
combustion tube, so that it rested on the constriction at C with a 
copper spiral, which is not drawn in the figure. At the lower end 
of the combustion tube a combustion capillary D of 3 mm. bore 
