22 MOTION OF THE JUICES OF THE ANIMAL BODY. 



bution is mutual, because their particles may move in all directions, and that 

 consequently saline particles move towards aqueous particles, as well as aqueous 

 towards saline particles, in virtue of their mutual attraction. 



From a solution of sulphate of copper in ammonia, placed in a tall glass cylinder, 

 there is gradually separated, if we pour a stratum of alcohol on the surface, and if we 

 prevent -the formation of a coherent crust which impedes the contact of the liquids, 

 the whole of the ammoniated sulphate of copper, while the deep blue solution 

 becomes colorless, because by the distribution of the alcohol through the solution 

 a mixture is formed, in which the salt is insoluble. 



The v rapidity of mixture of two liquids depends on the degree of their chemical 

 affinity ;* and the unequal mobility of the particles of one or the other liquid has 

 a favorable or unfavorable influence on the result. 



When the one liquid is heavier than the other, and of tough, viscid consistence, 

 a much longer time elapses before the ingredients of the tougher or heavier liquid 

 reach the surface from the bottom of the vessel; and in this case the greater 

 density and the less mobility of the particles are obstacles to the mixture. 



On the other hand, if the heavier or more viscid liquid be placed above the 

 lighter, the mixture takes place rapidly ; at the points where both liquids are in 

 contact is produced a mixture, which, being heavier, descends, whereby the heavier 

 liquid above is continually brought in contact with new surfaces of liquid. 



The very same phenomenon is observed in solution.! A fragment of sugar, 

 when covered with water at the bottom of a narrow cylinder, dissolves very slowly, 

 while, if suspended just below the surface, it rapidly disappears. In the former 

 case there is produced round the sugar a thick syrupy viscid solution, which 

 protects the undissolved part of the sugar for a long time from contact with the 

 water ; in the latter there is formed at the surface a solution, which descends in 

 striae, and gradually disappears, while by the change of place thus induced, new 

 portions of water are constantly brought in contact with the undissolved sugar, 

 and are thus enabled to exert their solvent powers. 



If skin and membranes consist of a cohering system of very narrow tubes, it is 

 obvious, that when two dissimilar, but miscible liquids are separated by such a 

 tigs ae, the pores of the tissue will fill with each of the two liquids. In all situations, 

 \uiere the liquids came in contact in the substance of the membrane, a mixture 

 takes place, and this mixture is extended equally towards both sides. 



If there be brine on one side of the bladder, and water on the other, there must 

 be formed, in the middle, or at some point of the bladder, a diluted brine, which 

 or tne side in contact with the water yields salt to that water, while on the opposite 

 side the strong brine mixes with the diluted brine in the bladder. 



The substance of the bladder has no influence on this mixture, because it can 

 produce no change of place on the part of the saline or aqueous particles, for this 

 is the result of the chemical affinity acting between the particles of salt and those 

 of water. 



J Now since the rapidity of the mixture of two liquids stands in a direct pro- 

 portion to the amount of surfaces coming into contact within a given time, and 

 since the liquids, separated by a bladder, can only come in contact through its 

 pores, while the number of points of contact is diminished by the presence of the 

 non-porous parls of the bladder, it follows, that, exclusive of all other effects, the 

 time required for mixture must be lengthened by the interposition of a bladder. 

 In the absence of the bladder, the mixture would take place exactly as when it is 

 present, except in regard to time. 



When the heavier brine is under, the water above the bladder, the two liquids 

 mix more slowly than without the bladder. 



But since a bladder, inasmuch as a feeble hydrostatical pressure is not propagated 

 through its pores, allows us to place a heavier liquid above a lighter, and to retain 



* Mixture is influenced by chemical affinity, by unequal mobility, and by unequal density in 

 the liquids. 



t Effect of position on the solution of a solid. 

 $ Rapidity of mixture. 



