171 
glass and steel, and continued to close after it had been cooled, up 
to a pressure of 150 atmospheres. 
Now the apparatus ABS was slid into the tube; it rested on the 
constriction C by means of a loose glass tube that tightly fitted in 
the copper tube; the length of this tube was chosen so that the end 
of the manometer needle was exactly between the two glass plates 
in the holes in the screws, so that it was possible to read the 
position with an ineandescent lamp placed behind it. The narrow 
copper tube D, which formed the connection with the CAILLETET- 
pump, was fastened to the lower end of the copper tube by means 
of a screw. Now the tube was quite filled with the glycerin water 
solution, and closed at the top with a screw. 
So in this way we had obtained an arrangement which could 
resist pressures of about 150 atmospheres. It only remained to us 
to find a method to heat this copper tube to varying temperatures. 
We have tried to use an oil-bath for the heating, and to place 
the tube in the bath in such a way that the end in which the glass 
plates were, projected above the bath. This was required for the 
accurate reading of the needle, and to have at the same time an 
opportunity to clean the glass panes when in course of time the 
screws began to leak a little in consequence of the increase of tem- 
perature. This method of heating, however, appeared to give un- 
reliable results in spite of different modifications. It appeared that 
the part that projected above the liquid caused a loss of heat, 
so that the temperature of the nitrogen tetroxide remained lower 
than the temperature in the oil-bath, so that at a definite tempera- 
ture always too low pressures were found compared with the 
results according to the method a. | 
At last we were more successful with another quite different 
method of heating. The copper tube ‘was quite surrounded by 
two tightly fitting spirals of hard lead. Through both these 
spirals an oil-stream was passed, so that the two streams ran in 
opposite directions; one stream flowed spirally round the tube from 
below upwards, the other in the opposite direction. The oil-stream 
was obtained by means of a rotating pump worked by an electro- 
motor, which pressed the cil from a pan heated by two Tecluburners 
through the spirals. The tube and the heating-spirals surrounding it 
were first enveloped with thick asbestos cord, and then with a 
thick layer of cotton waste to prevent emission of heat as much as 
possible; the inlet and exit tubes were isolated in the same way. 
The temperature was read on an Anschiitz thermometer, which 
was placed between the spirals and the tube and of which the part 
d 12 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
