90 Prof. A. J. Brown. Selective Permeability of the [Jan. 23, 



Table VI. 



OOlUutr. 



Percentage of water absorbed during — 



2 days. 



4 days. 



7 days. 



9 days. 



10 days. 



11 days. 





33 -5 



43 -9 



51 -5 



57-6 



59 -5 



63 -4 



NaCl 



28 -2 



31 -9 



34 -1 



35 -2 



35 -7 



36 -0 





40-1 



53 -6 



63 -8 



68 -6 



69 -0 



70 -3 













11 days. 



13 days. 





37 -4 



45 -1 



52 -8 



55 -1 



58 -1 



61 -4 



NaCl 



30 -9 



34 -4 



35 -8 



36 -8 



36 -5 





Trichloracetic Acid. — This acid was chosen on account of its similarity in 

 configuration to acetic acid, from which it is distinguished, however, by being 

 a strong electrolyte, acetic and the other acids and the salts which diffuse 

 through the seed-coverings being all weak electrolytes. 



On immersing seeds in a solution containing 5 per cent, of the acid, it was 

 found to enter them very rapidly, so much so that after 48 hours they were 

 saturated with it. This result was clearly not due to any destructive action 

 of the acid on the seed-coverings, as when seeds saturated with a solution of 

 trichloracetic acid were immersed in a solution of sodium bicarbonate, the acid 

 within the seeds remained unaffected even after the lapse of 10 days. In 

 a control experiment, seeds impregnated with acid, of which the coverings 

 were intentionally damaged, were placed in a solution of the bicarbonate ; 

 this soon entered the seed and in a few hours neutralised the acid. Trichlor- 

 acetic acid is the only strong electrolyte which has been found to possess the 

 property of diffusing into the seed system. 



Ammonia. — The membrane is more or less injured by exposure of the 

 seeds in solutions of ammonia of weight normal strength, as acid penetrates 

 into the corns after they have been steeped in such a solution. On the other 

 hand, when corns which had been steeped in one-half or one-quarter normal 

 solutions of ammonia were dried and then exposed in a normal solution of 

 sulphuric acid during 48 hours, no acid was found to enter. The velocity 

 with which water is absorbed from solutions of ammonia is remarkable, as 

 shown by the results recorded in Table VII. 



The ammonia passes into the corns with the water ; on the other hand, 

 when the corns impregnated with ammonia are placed in a normal solution of 

 sulphuric acid, after 24 hours they are no longer alkaline internally, the 

 ammonia having passed out in the reverse direction. 



