DIFFUSION TAKES PLACE BETWEEN THE PARTICLES OF HETEROGENEOUS BODIES. 23 



richer gas would escape, and its place be taken by common air. We therefore con- 

 sider this a case in which equilibrium has not ensued, progress only being made to- 

 wards it, the decomposition and apparent anomaly being only the result of a more ready 

 solubility and rapid passage of one gas. By taking advantage of this, it is possible to 

 obtain from the atmosphere oxygen of some purity. If a volume of atmospheric air be 

 agitated with boiled water in a close vessel, it will be found that a rapid absorption of 

 its oxygen ensues, while but little nitrogen is imprisoned among the pores of the liquid. 

 This gas, by the action of heat, may be driven off from the water, and being subjected 

 to another washing, may be rendered still more pure ; by successively washing and 

 rejecting the nitrogen left, a gas so rich in oxygen may be procured as to be equal to 

 some that is obtained by other processes, as by the action of sulphuric acid on perox- 

 ide of manganese. 



CHAPTER IV. 



ON INTERSTITIAL MOVEMENTS, being a Continuation of the preceding Chapter. 



(From the American Journal of the Medical Sciences for May, 1836.) 



CONTENTS : Diffusion takes place between the Particles of Heterogeneous Bodies. Dif- 

 fers from Chemical Attraction.^ Action of Binary Arrangements. Action of Ternary 

 Arrangements. Decompositions by Binary Arrangements. Decompositions by Ter- 

 nary Arrangements. 



64. IF we could place a known volume of vapour in the centre of an extensive void, 

 where no disturbance from without could solicit its particles to move in one direction 

 rather than another, it is to be supposed that, conformably to certain laws that are 

 known to obtain and operate on bodies of an aerial constitution, movement would en- 

 sue. To an assignable limit the vapour would expand, by a species of repulsion of its 

 own particles. In the immense vacuum in which the solar system moves, there are orbs 

 that seem to fulfil this condition ; these, though they wander through very large 

 paths, and are disturbed by the reaction of bodies they move past, sufficiently approxi- 

 mate the circumstances here laid down to show that there is an extent beyond which 

 bodies so constituted are not disposed to expand. Astronomical observations also show 

 that gases such as our own atmosphere is composed of do not by their expansion tres- 

 pass beyond a given point into a void, for then the laws upon which they are formed 

 react, as the firmest barrier from without would do, to prevent their farther expansion. 



65. An orb so constituted could not, in any length of time, undergo any change of com- 

 position, structure, or figure ; for, so soon as the first motion which decided its equilibrium 

 was over, that equilibrium would remain undisturbed, unless forces from without were 

 brought to bear upon it. In a void such as we are here supposing, apart from any such 

 derangement, equally a void as to force as well as to matter, the vaporous mass could 

 not be subject to any contingency. 



