CONDITION OF EQUILIBRIUM. 17 



pneumatic trough and exposed to the free atmosphere, I placed 100 measures of atmo- 

 spheric air and 42 of hydrogen gas, being anxious to see if any passage of the gases 

 would ensue, as the oxygen and hydrogen in the mixture were in nearly a due propor- 

 tion to form water. Motion at once began, the level of the water in the tube rising for 

 several hours. In the course of a few days, only a trace of hydrogen was discoverable, 

 the remaining gas differing very slightly from atmospheric air. The same was repeated 

 with a tube closed by a serous membrane, kept continually moistened; when all motion 

 appeared at an end, analysis showed that there was only T ' 7 th of the whole volume of 

 hvdrogen beneath the membrane. 



47. These experiments, which were repeated again and again with the same results, 

 establish an important doctrine. If a gas be confined beneath a system of pores, the 

 other extremity of which communicates with another gas, movement will ensue, until 

 the constitution of the gas on both sides of the system is alike. If oxygen and hydro- 

 gen be thus placed, they will mutually pass to each other, nor will that motion cease 

 until the resulting compound on both sides of the membrane is the same chemically. 

 This endeavour to an equalization of constitution takes place under all circumstances ; 

 it may. perhaps, be partially arrested by the condensing action of the barrier. There 

 are. therefore, two prominent conditions under which the phenomena of endosmosis 

 may be regarded: 1st. During the state of motion. 2d. After an equilibrium is obtained. 



48. Aided by this principle, we can explain how mixtures of gases would comport 

 themselves when exposed to free atmospheres, or when shut up in close chambers. The 

 arrangement of (46) will serve as an illustration : here we have a mixture of atmospheric 

 air and hydrogen exposed to the free atmosphere. It is evident that, in pursuance of 

 an attempt to gain an equilibrium, a portion of air from the atmosphere should pass in- 

 ward through the membrane, and a portion of hydrogen pass out But as soon as the 

 hydrogen is beyond the outside of the membrane, it is dissipated by aerial currents, or 

 otherwise diffused in the mass of the atmosphere, the condition of equilibrium being in 

 nowise approached to, for so fast as the hydrogen escapes, it is carried off; there be- 

 ing continually hydrogen and atmospheric air on one side of the membrane, and only at- 

 mospheric air on the other. Equilibrium, therefore, can only be gained by the entire 

 dissipation of the hydrogen into the free air, and, accordingly, experiment indicates that 

 when that equilibrium is gained, the hydrogen has vanished, and atmospheric air is 

 found on both sides of the membrane. But very different would that action be if the 

 arrangements were included in a close chamber, as beneath a small glass bell ; here, 

 when the hydrogen comes out through the membrane, it does not escape, but continu- 

 ally accumulates, and motion ceases, and equilibrium is gained when the relative pro- 

 portion of the gases outside the membrane is the same as inside. Hydrogen, therefore, 

 in this case, is found on both sides of the barrier. 



49. Before proceeding to give an account of the chemical changes that may happen in 

 virtue of the action of capillary forces, it is necessary to remark, that all the analyses of 

 gaseous mixtures, in which oxygen is an element, have been uniformly made by means 

 of binoxide of nitrogen. Living in a climate where no dependance can be placed on the 

 action of an electrical machine, and not possessing Dr. Hare's galvano-ignition apparatus, 



C 



