DENATURING OF VEGETABLE PROTEINS 39 



this insoluble product would be increased by the addition of small 

 quantities of strong acid to the solution. This has been found to be 

 the case, and the following figures give the result of experiments which 

 have shown this : 



PERCENTAGE OF EDESTAN FORMED BY ACIDS AT 20. 

 9 c.c. HC1 i 4 c.c. HC1 i8c.c. ~ HNO, igc.c. HNO S aoc.c. HNO, 



100 100 100 100 100 



3 hours 20 hours 3 hours 20 hours 24 hours 24 hours 24 hours 



9-01 12-15 29-80 33-55 68-38 75-20 79-02 



These figures, compared with those of the preceding table, show that 

 edestin yields much more edestan in contact with acids than in contact 

 with water. In the experiment in which 9 c.c. of centinormal hydro- 

 chloric acid were used the proportion of edestan that formed was very 

 much less than in the experiment containing 14 c.c. of the same acid. 

 In the first experiment the amount of acid used was less than that 

 with which the edestin can combine to form a water-soluble compound, 

 and the solution therefore contained only so much free acid as was 

 produced by hydrolytic dissociation of the edestin salts. In the experi- 

 ment with 14 c.c. of acid a small amount of acid in excess of that re- 

 quired to form a soluble compound was present, and the effect of this 

 larger quantity of free acid produced by the greater hydrolysis of the 

 weaker acid compounds of edestin is made very manifest in the greatly 

 increased quantity of edestan which was produced. 



That the amount of edestan which is formed depends on the degree 

 of ionisation of the acid which produces it is shown by the following 

 experiments, in which portions of neutral edestin, each weighing I 

 gramme, were suspended in 6 c.c. of water and 14 c.c. of centinormal 

 hydrochloric, phosphoric and acetic acids were respectively added. 

 The quantity of edestan that had formed after frequently agitating 

 during two hours is given in the following table : 



PERCENTAGE OF EDESTAN FORMED BY EQUIVALENT QUANTITIES OF DIFFERENT ACIDS 

 UNDER THE SAME CONDITIONS. 



HC1 H,PO 4 H 4 C 9 O 2 



14 c.c. 14 c.c. * * 14 c.c. 4 8 2 



100 IOO IOO 



19-29 16-02 5-65 



The solution of phosphoric acid contained 0*98 gramme of H 3 PO 4 

 per litre and was made on the assumption that this acid would behave 

 toward edestin as a monobasic acid. The quantity of edestan formed 

 by acetic acid as compared with that formed by hydrochloric acid 

 corresponds with the lesser ionisation of the former acid. 



The edestan which is contained in preparations of edestin, made by 



