CHANGE OF MIXTURE IN LIQUIDS. 23 



it in that position; this circumstance has the effect of promoting mixture, the 

 ultimate cause of which is, not the bladder, but the specific gravity of the liquid.* 

 The bladder is a means of enabling the specific gravity to influence mixture. The 

 foregoing remarks appear to me sufficiently to elucidate the share taken by the 

 bladder in the mixture of two dissimilar liquids placed on opposite sides of "it. 



With respect to the change of volume in the two liquids which become mixed 

 through the bladdeis, we must consider, that the moistening or absorbent power of 

 a solid body, as well as the power of a liquid to moisten other bodies, is the 

 result of a chemical action.t Liquids of different properties, or of different 

 chemical characters, are attracted with unequal degrees of force by solid bodies, 

 and exert towards them unequal degrees of attraction, and if we alter even in a 

 system of capillary tubes, filled to a certain height with a liquid, the chemical 

 nature of that liquid, we change thereby the height at which the liquid stands. 

 In an animal tissue saturated with water, the water is prevented from flowing out 

 by the mutual attraction, and by the capillary force, but if the attraction of the 

 organic parietes for water be diminished by the addition of alcohol or of salt to the 

 water, a part of it flows out. To this must be added, that the water absorbed by 

 an animal texture when it enters the capillary tubes, exerts, in virtue of its attrac- 

 tion for the tubes, a certain pressure, by which the vessels are swoln and enlarged. 

 The particles of liquid in these tubes undergo a counter-pressure from the elastic 

 parietes, by which pressure, when the attraction of the liquid particles for the 

 solids is diminished by any new cause, the amount of expelled fluid is increased. 



The organic parietes of the tubes, saturated with water, are affected by alcohol 

 just as a salt is when dissolved in water. On the addition of alcohol, or of 

 another liquid, the water separates from the salt, or from the parietes, or the parietes 

 separate from the water. 



If the animal tissue possessed as great an attraction for the newly-formed mixture 

 as for the water alone, the volume of the liquid would not change. The mixture 

 would take place, but no water would flow out. 



A bladder, saturated with water, when brought in contact with alcohol, shrinks 

 together, a part of the water separates from the animal matter, but there always 

 remains in the bladder a certain amount of water, corresponding to its attraction 

 for the bladder and for the alcohol; just as the solutions of many salts which have 

 a strong attraction for water (such as a metaphosphate and acid phosphate of soda,) 

 and are insoluble in alcohol, are separated by the addition of alcohol into two strata 

 of liquid, the heavier of which is a more concentrated solution of the salt in water, 

 containing a little alcohol, while the other, the lighter, is an aqueous liquid con- 

 taining much alcohol. The alcohol and the salt divide between them the water of 

 the solution. 



When we add, to a mixture of equal parts of acetone and water, a certain quan- 

 tity of dry fragments of chloride of calcium, the first fragments which are added 

 deliquiesce and dissolve entirely in the mixture.^ But if we go on adding the salt, 

 a separation soon occurs, two strata of liquid are formed, of which the upper con- 

 tains acetone and water, the other is an aqueous solution of the chloride with a 

 little acetone. If we add still more of the chloride, water is abstracted from the 

 acetone of the upper stratum, and when a proper quantity has been added, the 

 acetone retains no trace of water. 



If we suppose, that of the two originally formed strata of liquid, one of them, 

 namely that which sinks and contains chloride of calcium dissolved, is in contact 

 with a current of dry air, the water of this solution will evaporate, the solution will 

 thus become stronger, and in consequence of its increased concentration will be 

 able to remove a new portion of water from the mixture of acetone and watei 

 above it ; and this will continue till the acetone is entirely deprived of water. 



If in the place of the chloride of calcium we put a bladder, and, in place of the 

 acetone and water, diluted alcohpl, we have the finest example of the unequal 



*In certain circumstances, the interposition of a membrane accelerates mixture. 

 fChange of volume in liquids which mix through a membrane is the result of chemical affinity 

 modifying capillary attraction. 

 J Action of chloride of calcium on a mixture of acetone and water. 



