On the Liquefaction and Solidification [1 844, 



through a failure of the cement. Hence the cement joints 

 should not be used for long experiments, but only for those 

 enduring for a few days. 



Oxygen. Chlorate of potassa was melted and pulverized. 

 Oxide of manganese was pulverized, heated red-hot for half an 

 hour, mixed whilst hot with the chlorate, and the mixture put 

 into a long strong glass generating tube with a cap cemented 

 on, and this tube then attached to another with a gauge for 

 condensation. The heat of a spirit-lamp carefully applied pro- 

 duced the evolution of oxygen without any appearance of water, 

 and the tubes, both hot and cold, sustained the force generated. 

 In this manner the pressure of oxygen within the apparatus 

 was raised as high as 58*5 atmospheres, whilst the temperature 

 at the condensing place was reduced as low as 140 Fahr., 

 but no condensation appeared. A little above this pressure 

 the cement of two of the caps began to leak, and I could carry 

 the observation no further with this apparatus. 



From the former scanty and imperfect expressions of the 

 elasticity of the vapour of the condensed gases, Dove was led 

 to put forth a suggestion*, whether it might not ultimately 

 appear that the same addition of heat (expressed in degrees of 

 the thermometer) caused the same additional increase of ex- 

 pansive force for all gases or vapours in contact with their 

 liquids, provided the observation began with the same pressure 

 in all. Thus to obtain the difference between forty-four and 

 fifty atmospheres of pressure, either with steam or nitrous 

 oxide, nearly the same number of degrees of heat were re- 

 quired ; to obtain the difference between twenty and twenty- 

 five atmospheres, either with steam or muriatic acid, the same 

 number were required. Such a law would of course make the 

 rate of increasing expansive force the same for all bodies, and 

 the curve laid down for steam would apply to every other 

 vapour. This, however, does not appear to be the case. That 

 the force of the vapour increases in a geometrical ratio for 

 equal increments of heat is true for all bodies, but the ratio is 

 not the same for all. As far as observations upon the follow- 



* Poggendorff 's Annalen, xxiii. 290 ; or Thomson on Heat and Electri- 

 city, p. 9. 



