DETERMINATION OF IIYDROLYTIC DISSOCIATION OF SALT-SOLUTIONS. 



245 



sufficient to say that a formula can be deduced for the reaction, and thai 

 Shields found it contirmed by experiment. 



In spite of the complicated nature of the reaction, very good results 

 can be obtained by this method. The saponification proceeds very much 

 more quickly under the influence of hydroxyl ions than of hydrogen ions, 

 and so the measurement of even very small degrees of hydrolysis can be 

 carried out at the ordinary temperature, which is not the case in the 

 method mentioned previously. Shields was able to measure even such a 

 small degree of hydrolysis as that of sodium acetate — rather less than 

 0*01 per cent, in ^\, normal solution. This is a degree of precision which 

 greatly surpasses that of any determinations of free acid by the catalysis 

 of esters or of cane sugar. 



Shields showed that the velocity of saponification was not disturbed 

 by the presence of ester and alcohol. He further showed by this method 

 that trisodium phosphate, Na^PO.,, is quantitatively split up in aqueous 

 solution into NagHPO^ and NaOH. 



According to Ley,^ the saponification of esters sometimes takes place 

 even under the influence of neutral salts, such at KCl at 100°. It is 

 doubtful whether this points to a slight hydrolysis of the salts at this 

 temperature, which seems very improbable, or whether in certain cases 

 otiier ions besides hydrogen and hydroxyl can act as catalysers in 

 saponifying esters. In any case the velocity of the reaction is very small 

 as compared with that brought about by salts which are ki^own to be 

 hydrolysed. 



The following tables give the percentage of hydrolysis of a number of 

 salts of weak acids and bases as determined by this method by Walker 

 and others. For the sake of comparison the values have all been recal- 

 culated, so that the figures give the hydrolysis in jiy normal solution. 



-Hydrolysis of the hydrochlorides of weak bases as measured by the 



catalysis of esters. 



Temperature = 25°. 



Name of base. 



Thiazol 

 Glycocoll 

 Asparagine . 

 ThiohydantoiQ 

 Asparaginic Acid 



Percentage hydro- 

 lysis of Hydrochloride 



solution. 



10 



17 

 19 

 25 

 30 

 31 



Name of base. 



Acetoxime . 

 Urea 



Acetamide . 

 Propionitrile 

 Thiourea 



Percentage hydro- 

 lysis of Hydrochloride 



in — solution. 

 10 



. 30 



. 90 



. 98 



. 99 



. 99 



II. — Hydrolysis of the alkali salts of weak acids as measured by the 

 saponification of esters. 



Temperature = 2-5°. 



Zcittcltr. fiir 2>nys. Chcm., 30, 230 (1899). 



