144 Mr. H. E. Roaf. The Vapour- Pressure 



to the osmotic gradient. The time required to reach osmotic equilibrium in 

 the fibril (column 17) is calculated by dividing three days, in seconds, by 

 the relative surface through which unit volume passes (column 14) and also 

 by the relative driving force (column 15). 



In the case of the diffusion of acid, the acid must diffuse through the 

 thickness of the paper before it can affect the contents of the osmometer. 

 Therefore, in calculating the time required to reach equilibrium, the distance 

 must be taken into account a second time. For this reason the equilibrium 

 for acid will be reached in inverse proportion to the square of the distance 

 (square of column 15). The length of time required to reach equilibrium 

 for lactic acid in the muscle (column 16) is found by dividing 14 days, in 

 seconds, by the relative surface through which unit volume passes (column 14), 

 and also by the squares of the figures in column 15. 



In order to control the above calculation the rate of diffusion of lactic 

 acid was measured by allowing it to diffuse into gelatine containing an 

 indicator. A 2-per-cent. solution of gelatine was coloured by Congo red, 

 and tubes 3 mm. in diameter were filled with it. After the gelatine had 

 solidified, the tubes were cut into short lengths and placed into 25 c.c. of 

 solution. The length of tube in which the indicator had changed colour was 

 measured at definite time-intervals. 



Two tubes were placed in each flask, two flasks of each solution were used, 

 and there were two ends to each tube, therefore the measurements are the 

 average of eight determinations in each case. 





'05 N lactic acid. 



'02 N lactic acid. 



-01 N lactic acid. 



hours. 

 1 

 4 

 25 



mm. 

 3-4 



7 -0 (2 x 3 -5) 

 17 '0(5x3 -4) 



mm. 

 2-6 



5 -5 (2 x 2 -75) 

 14 (5 x 2 -S) 



mm. 

 2-0 



4 -0 (2 x 2 -0) 

 10 -1 ( 5 x 2 -0) 



A second experiment was carried out, but neutral red with sufficient alkali 

 to cause a yellow colour was used. The diffusion was slightly slower, possibly 

 because some of the acid was lost by neutralising the alkali. 





-05 N lactic acid. 



-02 N lactic acid. 



-01 N lactic acid. 



hours. 

 1 



4 

 25 . 



mm. 

 3 -2 



6 -2 (2 x 3 -1) 

 15 -4 (5 x 3 -1) 



mm. 



2 -3 



4 -6 (2 x 2 -3) 

 12 -1 (5 x 2 -4) 



mm. 

 1 -6 



3 -4 (2 x 1 -7) 

 9 -9 (5 x 2 -0) 



The results show very clearly that the time required for diffusion is 



