M. Regnault on the Elastic Force of Vapours, 279 



Academy) on the determination of the latent heats of evaporation, 

 nnder different pressures, of very volatile liquids, and on the quan- 

 tities of heat which these gases absorb under pressure. I shall 

 briefly describe the method adopted. 



I prepare carbonic acid by a regulated and continuous addition 

 of dilute hydrochloric acid to broken marble placed in a large 

 flask. The solution, freed from acid and charged with chloride 

 of calcium, flows out as fast as it is produced, and the gas passes 

 into a gas-holder of a cubic metre capacity. A force-pump, with 

 several barrels, and worked oy my steam-engine, draws the gas 

 in the gas-holder, having made it previously traverse several 

 drying materials. It forces the gas into a first receiver of 3 

 or 4 litres capacity, which simply serves as regulator. The gas 

 then passes freely into the apparatus in which it is to be con- 

 densed, and which is placed in a mixture of ice and crystallized 

 chloride of calcium. The non-condensed gas passes into a second 

 closed receiver of 5 litres, placed at the end of the apparatus. 

 This serves to receive the air and the non-liquefiable foreign 

 gases, which can be allowed to escape from time to time by 

 opening the stopcock. 



Protoxide of nitrogen and bisulphuretted hydrogen can be 

 liquefied in large quantities by the same arrangement. But for 

 gases which readily alter in contact with fatty matters, I employ 

 a special force-pump, in which the gas is only in contact with 

 mercury. This pump consists of two equal barrels of cast iron, 

 joined so as to be U-shaped. The first barrel contains a solid 

 piston, which in its motion simply acts on a quantity of mercury 

 which exactly fills one of the barrels. The system of two 

 valves, exhausting and forcing, is arranged in the second barrel. 

 It is evident that by this means the gas never comes in contact 

 either with the piston or the greased sides. 



I have been especially interested in liquid ammonia, in con- 

 sequence of its great calorific capacity, of its great latent heat 

 of evaporization, and of the ease with which it is obtained and 

 afterwards collected in the gaseous state. I propose to use it 

 principally in obtaining very constant low temperatures by 

 causing it to boil under different pressures. I prepare ammo- 

 niacal gas by causing a stream of strong liquid ammonia to fall into 

 a copper vessel contained in a small boiler in which water 

 is kept boiling by means of a gas-lamp. The vessel is con- 

 sequently always surrounded by the vapour of boiling water ; 

 the ammonia flows in a spiral along the sides ; and the liquid, 

 which is almost freed from ammonia, runs out by a tube at the 

 bottom, which plunges to a depth of several decimetres in cold 

 water. The ammoniacal gas exhausted by the pump passes 

 through several copper receivers full of fragments of soda-lime ; 



