JACQUES LOEB 721 



we shall show later that the correctness of the assumption concerning 

 the sign of the charge of the molecules of water can be proved 

 directly by experiments on electric endosmose. 



//. Observations on the Rate of Filtration. 



Collodion bags in the form of Erlenmeyer flasks of a content of 

 about 50 cc. were prepared in as uniform a way as possible and were 

 used after several days testing. Fresh bags were usually too per- 

 meable to serve for our purpose. The mouth of the collodion bag 

 was closed with a perforated rubber stopper and the mouth of the 

 bag was fitted tightly to the stopper with the aid of rubber bands. 

 Through the hole in the stopper a glass tube with a bore of about 2 

 mm. in diameter was pushed into the bag. The collodion bag was 

 filled with distilled water which reached into the glass tube to a height 

 of about 110 mm. above the level of the distilled water of a beaker 

 into which the bag was dipped. This pressure head of about 110 

 mm. of water inside the bag increases the number of particles im- 

 pinging during the unit of time on the unit of area of the inside of the 

 collodion bag and as a consequence more water diffuses in the unit 

 of time from the bag into the beaker than diffuses in the opposite 

 direction. Consequently water diffuses out and the pressure head on 

 the water in the bag diminishes constantly. By measuring the level 

 of the water in the glass tubes at definite intervals and plotting the 

 values of the level as ordinates over the time as abscissae we get a 

 picture of the rate of diffusion of water out of the bag (Fig. 1). 



When the outside solution is not distilled water but a solution of a 

 non-conductor, e.g. cane sugar, the rate of diffusion of water is 

 accelerated owing to the fact that the presence of sugar particles 

 diminishes the number of water particles which in the unit of time 

 impinge on the unit of area on the outside of the collodion membrane. 

 Hence if the inside of the bag contains water and if the pressure head 

 of the water inside the bag is at the beginning again about 110 mm. 

 of water, the difference in the number of particles of water impinging 

 on the inside remains the same as before while the number of water 

 molecules impinging on the outside is diminished through the presence 

 of the sugar particles. This diminution must be in proportion to the 

 concentration of the sugar solution. 



