MIXTURE OF TWO LIQUIDS THROUGH A MEMBRANE. 



17 



less or no salt, and therefore specifically lighter, which again comes in contact with 

 the bladder. As long as the motions just described are perceptible, we observe a 

 constant increase in the volume of the brine in the tube a (Fig. 4,) or a diminution 

 in the volume of the pure water in the vessel 6. When the motions cease, the 

 rise of liquid in the tube is arrested, and when this takes place, the two liquids 

 are found to possess almost exactly the same specific gravity. 



When the two strata of liquid on either side of the bladder are little different in 

 composition (as soon comes to pass in the experiment (Fig. 2) where the saline 

 contents of the liquid which fills the pores of the bladder can hardly vary from 

 that of the next stratum,) the mixture of the liquids takes place, but without further 

 change of volume. But when an exchange of the mixtures on the opposite sides 

 of the bladder can occur in consequence of their different specific gravity, and 

 when a continued difference between the strata on opposite sides of the bladder is 

 thus determined, then, so long as (in the case of brine and water, for example) one 

 side of the bladder is in contact with a concentrated, the other with a more diluted 

 solution, the change of volume in the two liquids continues. 



As appears from these experiments, the change of volume depends on a difference 

 in the character of the two liquids which are connected through the bladder ; and 

 the time during which change of volume occurs is in direct proportion to the time 

 during which this difference in character subsists. The greater the difference in 

 character and composition between the liquids, and the more rapidly this difference 

 is renewed by the exchange between the strata in contact with the opposite sides 

 of the bladder, the more rapidly does the one liquid increase, and the other 

 diminish in volume. 



The following apparatus is very conv-enient for measuring the 

 change in volume, caused by the mixture of two liquids separated by 

 a membrane.* 



The tubes a and 6, (Fig. 5) are of equal width, and are best takea 

 from the same tube ; a is closed with bladder, and filled up to a cer- 

 tain point with the liquid whose increase in volume is to be 

 determined. It is then fitted by means of a good cork into the wider 

 tube c, which contains distilled water, care being taken to exclude all 

 air bubbles. At d lies a small lead drop, which acts as a valve in 

 shutting the opening of the capillary tube connecting c with b. 

 Pure water is now poured into 6, and in order to keep in equili- 

 brium the lead drop at c?, rather more water is added than exactly 

 suffices to bring the liquids to the same level in both tubes. 



The liquid in a increases in volume, and the height to which it 

 rises may be read off by means of any division into equal parts 

 by measure ; the level of the liquid in b sinks in an equal ratio. If 

 we keep the liquid in 6, by the addition of fresh water, at the 

 original level, and if we ascertain the weight of the added water, 

 by pouring it out of a dropping bottle, and determining the loss of 

 weight in the dropping bottle, we learn, at the same time, the 

 weight and the volume of the water which has risen from c into a. 



Fig. 5. 



This apparatus admits, of course, of a number of variations and improvements. 

 I have employed it to determine the relation between brine and water, under the 

 circumstances just described. It appeared, among other things, that when the 

 tube a is filled with saturated solution of sea salt, the volume of the liquid increased 

 by nearly one half; that is, 200 volumes of such a solution increased to 300. 

 These determinations are, however, not the object of the present investigation, and 

 therefore I pass them over entirely. 



The following arrangement, (Fig. 6) will probably be found preferable to the 

 one just described, in many cases. Its construction depends on the observation, 

 that for the phenomenon itself, and for the result of the experiment, it is entirely a 



and after adding subacetate of lead as long as sulphoindigotate and sulphate of lead are 



precipitated, to separate the precipitate by filtration and dry up the filtered liquid in the 



water bath. A mere trace of the blue residue suffices to color blue large masses of liquid* 



* The change in volume may be measured. 



3 



