336 E. W. Dean — Esters of Substituted Aliphatic Acids. 



fication of the conductivity method of Walker* which has been 

 employed in the experiments of Findlay and Hickmansf on 

 the velocities of saponification of esters of hydroxy and alkvloxy 

 acids. The modification devised by the author simply adapts 

 the excellent procedure recommended by Walker to the cases 

 of the somewhat insoluble esters here examined. This proce- 

 dure was in outline as follows : 



Fiftieth normal solutions of carbonate-free sodium hydroxide 

 and of ester were first prepared. The conductivity apparatus 

 was of the usual form with a cell of the narrow Ostwald type. 

 The constant temperature bath was a mixture of cracked ice 

 and water which was vigorously and efficiently agitated with a 

 spiral stirrer operated by an electric motor. The initial con- 

 ductivity was obtained by measurements made on hundredth 

 normal sodium hydroxide solution. The cell was then care- 

 fully rinsed and dried. For the actual hydrolysis fifty cubic 

 centimeters of the fiftieth normal alkali solution were placed 

 in a clean and dry Erlenmeyer flask and suspended in the ice 

 bath. The fiftieth normal ester solution was likewise cooled 

 down to zero degrees in the same bath. 



At the proper time fifty cubic centimeters of the latter were 

 removed from its container by means of a pipette, run into the 

 alkali and the mixture vigorously shaken for a second or two. 

 The time at which the pipette was half empty was recorded as 

 beginning the reaction. As soon as was convenient a portion 

 of the reaction mixture was transferred from the flask to the 

 conductivity cell and bridge readings were taken at appropriate 

 intervals of time. The flask containing the remainder of the 

 reacting mixture was tightly corked and warmed in a water 

 bath for an hour or so to bring the action to completion. 

 After this it was re-cooled and measurements made upon por- 

 tions of its contents to obtain the final conductivity. Calcula- 

 tions were made in the same way as those of Walker except 

 that his scheme for their simplification was not adopted. Dur- 

 ing all the measurements a constant resistance of two hundred 

 ohms was kept in the box, thus eliminating the possibility of 

 slight errors due to this source. 



A trial experiment with ethyl glycollate showed that the 

 results obtained checked almost exactly with those of the titra- 

 tion method. Measurements were made with the esters of 

 alpha hydroxy-iso-butyric acid and of beta hydroxy-butyric 

 acid. The constants recorded for the other three esters are 

 from the results of titration experiments. 



In Table II are values of the constants obtained and the 

 time periods in minutes over which the reactions were followed. 



* Proc. Royal Soc, Series A, lxxviii, 155, (1908). 

 f Jour. Chem. Soc, lxxxvii, 747. 



