240 
Liquefaction of Oxygen. 
[April, 
approach each other as much as possible, certain indis- 
pensable conditions are necessary, which may be expressed 
thus ■ 
1. To have the gas absolutely pure, with no trace of 
foreign gas. 
2. To be able to obtain extremely energetic pressures. 
3. To obtain intense cold, and to subtract heat at these 
low temperatures. 
4. To utilise a large surface for condensation at these low 
temperatures. 
5. To be able to utilise the rapid expansion of the gas from 
extreme condensation to the atmospheric pressure — 
an expansion which, added to the preceding means, 
will compel liquefaction. 
Having fulfilled these five conditions, we may formulate 
the following alternative : — 
When a gas is compressed to 500 or 600 atmospheres, and 
kept at a temperature of — ioo° or — 140°, and it is allowed 
to expand to the atmospheric pressure, one of two things 
takes place : — 
Either the gas, obeying the force of cohesion, liquefies, 
and yields its heat of condensation to the portion of 
gas which expands and loses itself in the gaseous form ; 
or, on the hypothesis that cohesion is not a general law, 
the gas must pass to the absolute zero and become 
inert, — that is to say, an impalpable powder. 
The work done by expansion will not be possible, and the 
loss of heat will be absolute. 
Struck with the truth of this alternative, which is rendered 
certain by thermo-dynamic equations based on accurate data, 
I have sought to produce a mechanical arrangement which 
should entirely satisfy these different conditions, and I have 
chosen the complicated apparatus of which the following is 
a brief description : — 
I take two pumps, P 3 and p 4 , for exhaustion and com- 
pression, such as are used industrially in my ice-making 
apparatus. I couple these pumps in such a way that the 
exhaustion of one corresponds to the compression of the 
other. The exhaustion of the first communicates with a 
tube (r) of i* 1 metres long and 12*5 centimetres in diameter, 
and filled with liquid sulphurous acid. Under the influence 
of a good vacuum the temperature of the liquid rapidly sinks 
to —65°, and even to — 73 0 , the extreme limit attained. 
Through this tube of sulphurous acid passes a second 
smaller tube (s), of 6 centimetres diameter, and the same 
