278 



M. Kegnault on the Elastic Force of Vapours. 



The temperatures refer to the air-thermometer. The ebulli- 

 tion of mercury is regular enough at pressures below that of the 

 atmosphere. Under the atmospheric pressure, jumpings com- 

 mence, and they increase in proportion as the pressure increases : 

 under a pressure of ten atmospheres the shocks are so violent 

 that they produce a noise like that of a hammer striking an anvil. 

 Every moment the apparatus may be expected to burst into 

 pieces. 



The condensation of the gases was effected in the same appa- 

 ratus which served to determine the tensions, and which was so 

 arranged as to be quite freed from the last traces of air or any 

 other gas which it might contain. The liquefaction of sulphurous 

 acid is readily effected at the ordinary atmospheric pressure, when 

 the apparatus is placed in a cooling mixture. For ammonia and 

 sulphuretted hydrogen the apparatus is placed in a mixture of 

 ice and crystallized chloride of calcium, and then the gas com- 

 pressed with a hand force-pump. Care must be taken that 

 the ordinary grease of the pumps is replaced by fixed oils which 

 are not saponifiable. By a pressure of 2 to 3 atmospheres the 

 desired quantity of liquid ammonia is obtained ; but for sulphur- 

 etted hydrogen the pressure must be raised to 7 or 8 atmo- 

 spheres. 



I have had occasion to liquefy these gases on a large scale for 

 researches (of which I shall presently lay the results before the 



