170 
read on an Anschützthermometer (which had been compared with a 
normal thermometer) the mercury bulb of which was ata level with 
the nitrogen tetroxide. 
For the determination of the pressure this was regulated by means 
of a CAILLeTET-pump in such a way that the needle was exactly 
between the marks on the tube A, and read on a ScuArrer and 
BUDENBERG metal manometer gauged by means of a pressure-balance. 
The liquids which we have used for heating, were successively 
alcohol, toluene, xylol, and aniline; the bumping was prevented by 
a stream of air-babbles, which were sucked in through the tube 
that passed through the stopper. 
The results obtained by this method, will be described in $ 4. 
The experiments arranged in this way always finished up with an 
explosion; the highest pressure we reached was 67 atmospheres. 
The critical pressure, however, lying higher, we were obliged to 
have recourse to another method for the determination of the higher 
vapour-tensions. 
b. In our further experiments we abandoned the use of a com- 
bustion tube, and replaced it by a copper tube. In this we had first 
of all to face the difficulty to arrange it in such a way that the 
reading of the position of the manometer needle was possible. For 
this purpose near the end of the tube two transverse tubes were 
adjusted, which could be closed by means of perforated screws, one 
of which (£) has been drawn in fig. 25. The hole through these 
screws was closed with a glass plate, which was pressed to the tube 
by the screw. To make this arrangement tight at high pressure was 
at first attended with great difficulties. We tried to reach this by 
screwing the glass plates to the tube between rings of leather; it 
was, however, impossible to get a sufficient closure in this way. 
Then we pressed the plates between plaster of Paris, and between 
copper, made soft by being made red-hot, always, however, with a 
negative result. After these futile attempts we cemented the plates in 
loose steel mountings, and screwed these mountings with copper plates 
into the tube. As cement we tried first a mixture of soluble glass, 
zinc oxide, and magnesium oxide; once we succeeded in this way to 
obtain a sufficient closure up to 100 atmospheres, generally, however, 
the soluble glass showed cracks, which allowed the liquid in the copper 
tube to get through on increase of pressure. At last we succeeded 
in cementing the glass plates into the steel mounting by means of 
an enamel obtained by melting from natrium- and potassium car- 
bonate, silicium oxide, and lead oxide. By heating with a Tecluburner 
this enamel melted, and entirely filled the narrow opening between 
