72 EVAPORATION THROUGH MEMBRANES. 



faces of the bladder, reaches the point at which the 

 brine flows through the pores of the bladder, then 

 the place of the water which evaporates is occupied 

 by brine. 



In fact, when the brine is coloured blue, we ob- 

 serve, after a few hours, that a blue stratum forms 

 within the tube, which constantly increases, till at 

 last the vessel of brine is emptied, and the tube is 

 entirely filled with brine. 



with one If the longer limb be immersed in bile instead of 

 brine, the tube fills with bile, and if we employ, for 

 closing one end, a membrane rather thinner than we 

 use for the other, from which the evaporation takes 

 place, and then place the end with the thinner 



and in oil. membrane in oil (oil of marrow), the tube gradually 

 fills w r ith oil. 



In all these cases, no air enters the tube, which 

 continues full of liquid, as it was at first. 



Effect of a If we connect the evaporation tube 



series of 



short tubes, by collars of caoutchouc with short 



both ends bits of tube (Fig. 15), full of water, and 



der. tied with bladder at both ends ; and 



if we immerse the last bit of tube in 



brine, urine, oil, &c., all these cells, 



and at last the evaporation tube itself, 



become gradually filled with brine, 



urine, oil, &c. 



Liquids T;h e most general expression for these experi- 



wards the ments and results is this ; that all liquids which 



membrane 



from which are in connection with a membrane from the surface 



