OF THE MODE OF PASSAGE OF LIQUIDS THROUGH PORES. 13 



CHAPTER III. 



ON THE INTERSTITIAL MOVEMENTS WHICH TAKE PLACE AMONG THE PARTICLES OF BODIES. 



(From the Journal of the Franklin Institute for March and July, 1836.) 



CONTENTS : Of the Mode of Passage of Liquids through Pores. Endosmosis. Perco- 

 lation through Gum Lac, Gold Leaf, Mica, etc. Slow Motions in the Parts of Solid 

 Bodies, as in Silver Coins. Percolation through India Rubber. -Conditions of Equi- 

 librium. Percolation through Masses of Water. Percolation through excessively thin 

 Films of Water, as Soap Bubbles. Analysis of Gas on the Exterior and in the Inte- 

 rior of the Soap Bubble. General Law of the Phenomenon deduced. 



35. THE interstices which exist in a great variety of bodies may be looked upon as an 

 extensive system of capillary tubes, into which we should be prepared to expect that 

 bodies of all kinds might pass. A drop of water placed upon a porous stone or a piece 

 of chalk, sinks into it rapidly, but the value of the observation is lost, because it is com- 

 mon. If that water contained a colouring matter, we should find that, in sinking into 

 the chalk, the colour would be left on the surface. But here, again, commonplace princi- 

 ples dictate a ready answer : the interstices of the chalk may be supposed to be too small 

 to admit the colouring matter to pass, or perhaps some incongruity of shape might afford a 

 barrier ; yet how, upon these principles, shall we explain that mercury and other bodies 

 remain unmoved upon the porous mass, and show no ability to go through it, when they 

 will pass with readiness into the densest and closest substances, as gold ? No principle 

 qf coaptation will explain why quicksilver will not rise in a tube of glass, or why water 

 rises at all. We are induced at once to refer the whole matter to the chemical condi- 

 tions of the bodies on which we operate, and we quickly infer that fluids do not pass 

 into pores by soaking or leakage, or any such commonplace principle, but that it is an 

 action determined by certain laws that have reference to the condition of each body sep- 

 arately, and their relation to each other. A question, therefore, naturally arises as to the 

 peculiar operation of those pores, and how changes in their position, size, and shape 

 affect the results of their action. A class of these phenomena is quite independent of 

 pores of any sensible size, where no leakage or oozing can be suspected. A piece of 

 sugar dissolving in water diffuses itself into every part of the menstruum. Among those 

 excessively small interstices that exist between the atoms of the water, its particles find 

 a dwelling, where they are sheltered from all those forces that act so energetically on 

 the great masses of matter. Independent of gravity, they move freely in every direction ; 

 and, far from settling in those positions to which they might tend from their weight, they 

 are simultaneously and equally found in every portion of the solvent. This condition 

 of things does not indicate a passive state, but would rather teach that a very active and 

 powerful force is in operation, a force that can neutralize the action of gravity and other 

 external agents. It is essential, therefore, clearly to understand the circumstances of 



