MIXTURE OF THE LIQUIDS. 15 



when the contact has lasted only the fraction of a second.* The brine filling th-; 

 open pores of the membrane mixes with the pure water, and the latter acquires a 

 certain quantity of salt. 



In like manner, the pure water acquires a saline impregnation, when it is placed 

 in the tube instead of brine, and the outer surface of the bladder is placed in con- 

 tact with solution of salt. 



When the tube, closed with bladder, and filled with brine, is left for a long time 

 with the closed end immersed in pure water, the amount of salt in the latter 

 increases, while that of the brine diminishes, till at last the two liquids, separated 

 by the bladder, contain the same relative proportions of salt and water. 



If the liquid in the tube contain, dissolved, other substances which give to it 

 properties different from those of pure water, and if these solutions be miscible with 

 water, the mixture of them with the water takes place exactly as in the case of 

 brine.t This is true of saline solutions of every kind ; of bile, milk, urine, serum 

 of blood, syrup, solution of gum, &c., on the one side, and pure water on the other. 

 The concentrated liquid loses, the water or diluted liquid gains, in regard to saline 

 impregnation. 



If we fill the tube with water, and place it in a vessel with alcohol, the water 

 becomes charged with alcohol, while the alcohol becomes diluted with water. 



There is observed, in these circumstances, that is, when two dissimilar liquids, 

 separated by a membrane, mix together, a phenomenon of a peculiar kind; namely, 

 in most cases a change of volume in both liquids, while the mixture goes on.J 

 The one liquid increases in bulk, and rises ; the other diminishes in the same 

 degree, and consequently sinks below its original level. 



This phenomenon of mixture through a membrane, accompanied with change 

 of volume, has been distinguished by DUTROCHET, under the name of ENDOSMOSIS 

 and EXOSMOSIS ; endosmose is the name given when the volume increases exos- 

 mose, when it diminishes. Very generally, however, we attach to these terms 

 the idea of the unknown cause or group of causes which, in the given case* produce 

 the change of volume ; in the same sense as that in which the term capillary action 

 includes the causes which determine the ascent of liquids in narrow tubes. 



In all cases^ the increase in volume of the one liquid is exactly equal to the 

 decrease in volume of the other, after making allowance for the contraction which 

 the liquids undergo by simple mixture (as in the case of alcohol and water, oil of 

 vitriol and water, &c.,) as well as by evaporation. The unequal concentration, or 

 the unequal density of the two liquids, has a decided influence on the rapidity with 

 which the change of volume takes place ; but this cannot be viewed as the cause 

 of that phenomenon. In most cases the denser liquid increases in volume, in others 

 the reverse occurs. 



When, for example, the tube contains brine, and' the outer vessel pure water, 

 the brine, that is the denser liquid, increases in volume ;[| but when the tube con- 

 tains water, and the outer vessel alcohol, the water, that is, the denser liquid, 

 diminishes in volume. 



With regard to the mixture of the liquids, the bladder takes a distinct share in 

 the process, inasmuch as it has pores, through which the two liquids are brought 

 in contact. 



With reference to the porosity of the bladder, the rapidity of the mixture of 

 the two liquids is directly proportional to the number of particles, which, in a 

 given time, come into contact ; it depends also on the surface (the size of the mem- 

 brane,) and on the specific gravity of the liquids. 



The influence of extent of surface on the time required for mixture requires no- 

 particular elucidation ; that of the unequal specific gravity is rendered evident by 

 the following experiments.^ 



* Saline solutions pass very rapidly through bladder. 

 fThe same is true of bile, milk, urine, serum, &c. 



t Change of volume when two dissimilar liquids mix through a bladder. 

 $ Endosmosis and Exosmosis. 



J The change of volume does not depend alone on the relative density of the liquids. 

 f Influence of the unequal density of the two liquids, when the lighter liquid is above the 

 membrane!. 



