750 LIQUEFACTION OF OXYGEN. 



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 tem- 

 perature of -100° 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 poAvder. 



The work done b}^ 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 arl*angement which should entirely satisfy these different con- 

 ditions, and I have chosen the complicated apparatus of which the following 

 is a brief description : — 



I take two pumps for exhaustion and compression, such as are used in- 

 dustrially 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 t e first communicates with a tube of 1.1 metres long and 

 12 5 centimetres in diameter, and filled with liquid sulphurous acid. Under 

 the influence of a good vacuum the temperature of this liquid rapidly sinks 

 to -65°, and even to -73°, the extreme limit attained. 



Through this tube of sulphurous acid passes a second smaller tube of 6 

 centimetres in diameter, and the same length as the envelope. These two 

 tubes are closed by a common base. 



In the central tube is retained compressed carbonic acid produced by the 

 reaction of hydrochloric acid on Carrara marble. This gas, being dried, is 

 stored in an oil gasometer of 1 cubic metre capacity. 



At a pressure of from 4 to 6 atmospheres the carbonic acid easily lique- 

 fies under these circumstances. The resulting liquid is led into a long copper 

 tube 4 metres in length and 4 centimetres in diameter. 



Two pumps, coupled together like the first, exhaust carbonic acid either 

 from the gasometer or from the long tube full of liquid carbonic acid. 



The ingress to these pumps is governed by a three-way tap. A screw 

 valve cuts off at will the ingress of liquid carbonic acid in the long tube ; it 

 is situated between the condenser of carbonic acid and this long tube. 

 When this screw valve is closed, and the two pumps draw the vapor from 

 the liquid carbonic acid contained in the tube 4 metres long, the greatest 

 possible lowering of temperature is produced ; the carbonic acid solidifies 

 and descends to about - 140°. The subtraction of heat is maintained by the 

 working of the pumps, the cylinders of which take out 3 litres per stroke, 

 and the speed is 100 revolutions a minute. 



Both the sulphurous acid tube and the carbonic acid tube are covered 

 with a casing of wood and non-conducting stuff to intercept radiation. 



