Notes. 433 



property by observing the volume occupied respectively by oil, 

 water, and mercury, first placed in a vacuum, and afterwards ex- 

 posed to the pressure of the atmosphere ; but the results which 

 he obtained, though exact in themselves, were, however, liable 

 to be affected by the accidental variations of form and tempera- 

 ture to which the apparatus was subject. M. Oersted completely 

 removed these difficulties by plunging the liquid to be compressed, 

 together with the vessel containing it, into another liquid to which 

 the pressure was applied, and through which it was made to pass to the 

 interior liquid without changing the form of the vessel, since it acted 

 equally within and without. M. Oersted found, likewise, that a pres- 

 sure equal to the weight of the atmosphere produces in pure water a 

 diminution of volume equal to 0,000045 of its original volume. The 

 experiments of Canton gave 0,000044. M. Oersted found, by vary- 

 ing the pressure from i of the weight of the atmosphere to 6 atmos- 

 spheres, a change of volume sensibly proportional to the pressure. 

 Later experiments, made by Mr Perkins, seem to show that this pro- 

 portionality continues when the pressure amounts to 2000 atmos- 

 pheres. Before the water, however, is entirely freed from air, the 

 diminution of volume, produced by the pressure, is at first somewhat 

 greater than the above ratio would indicate. 



HI. 



On the Condensation of Gases into Liquids. 



MR FARADAY enclosed in glass tubes, bent and sealed, different 

 ehemical products which were capable of developing gases by their 

 mutual combination. He introduced them into the tubes in such a 

 manner that they remained separate in the different branches of 

 each tube, and were not mixed until the tube had been sealed. All 

 the gas developed in each tube was found to be confined to a fixed 

 volume, to which it could be reduced only by the action of a con- 

 siderable pressure ; this pressure causes it to liquify in the follow- 

 ing cases. 1. Sulphurous acid produced by the action of sulphuric 

 acid on mercury. 2. Sulphuretted hydrogen produced by the action 

 of hydrochloric acid on the sulphuret of iron in fragments. 3. Car- 

 bonic acid produced by the action of sulphuric acid on carbonate of 

 ammonia. 4. Oxide of chlorine, produced by chlorate of potash and 

 sulphuric acid. 5. Ammonia disengaged from the combination of 



Mech. 55 



