( 216.) 
is to compare the capacity of the same condenser in air and in a 
given medium when all dimensions are kept strictly constant. When 
the capacity of the air condenser is obtained at the room tempera- 
ture, and that of the liquid condenser at the temperature of boiling 
gases the geometrical proportions are probably altered by thermic 
expansion and deformation, and in consideration of the large difte- 
rence of temperature it is possible that an appreciable error may 
thus enter. 
For these reasons the condenser was arranged in the hollow cylinder 
so that this enclosed space could be evacuated and cooled in liquid 
gas. Then, in the manner described below, this evacuated space con- 
taining the condenser could be filled with liquid gas from the beaker. 
It must be noticed that, however thin the leads may be they always 
will represent a measurable capacity and hence that the smallest dis- 
placement of the apparatus will produce considerable errors. Especially 
to avoid this it is desirable to mount the apparatus as in ONNES’ 
method for the use of liquid gases in measurements. According to 
this method, the apparatus to be dipped in and filled with liquid 
gas is mounted in the closed boiling case, in which the liquid can 
be immediately poured out, so that the operations of exhausting 
cooling and filling with the liquid gas allow the position of the 
condenser and the leads to remain unaltered. 
The manner in which the above mentioned hollow brass cylinder 
is mounted with the experimental condenser in the boiling glass is 
given in Comm. N°. 51 82%. The further arrangement of the 
covering of the condenser is shown in Plate I. The inside of the 
cylinder communicates with the exterior in two ways. One is the fine 
copper tube # which communicates with the part of the beaker un- 
occupied by the cylinder. This can be opened or closed at pleasure 
from without by means of a cock in which the pin 4 is moved by 
the rod hg and handie A3. The other outlet is the glass tube g, 
through which the expanding vapours can be drawn towards u to 
be collected in the caoutchouc bags ®). 
1) Plate I is a detailed drawing of the cryostat containing the condenser. Plate IV is 
a diagramatie representation of the nitrous oxide circulation and the cryostat, for the 
oxygen circulation see Maruias |. c. 
2) Further explanations:- a, are small screws to fasten packing a,, 4 wooden block 
to support glass tubes 2, which the. wires d, and d, pass through, ¢ wooden block 
in two parts to support outflow tube without conducting of heat, f soldered in screw 
used in boring the canal for the liquid gas, #, packing under the level, 4, brass 
mount for screwing on the same, % leather cushion, e caoutchouc tube to connect 
the glass tube g with the brass covering of the condenser and protected by fishglue 
against the liquid gas. ¢, brass bands to make all tight with the help of the screws 
