E. W. Dean — Esters of Substituted Aliphatic Acids. 333 



with approximately tenth normal baryta water. The initial 

 titration will then be about twenty-five cubic centimeters, the 

 final at least fifteen cubic centimeters greater. With a range 

 of this magnitude the constant error of titration does not cause 

 undue irregularity among the constants obtained. Saturated 

 solutions of ethyl butyrate or ethyl iso-butyrate (in decinormal 

 hydrochloric acid) are only two to three hundredths normal, 

 and the range in the titrations, measured in tenth normal barium 

 hydroxide solution, is from five to seven and a half cubic centi- 

 meters. This is inconveniently small, and three modifications 

 have been tried to increase it. First, fifteen cubic centimeter 

 portions were titrated with twentieth normal alkali. The 

 advantage here is slight but definite, the range increasing by 

 one-fifth and the error remaining about the same. 



Next, a modification of the method of De Hemptinne was 

 tried.* A twenty-five cubic centimeter portion of the reaction 

 mixture was treated with twenty-five cubic centimeters of 

 tenth normal baryta water and the titration completed with a 

 twentieth normal solution of the same alkali. This doubles the 

 range, but unfortunately largely increases the error of titration. 



The third and most satisfactory method involved the use of 

 twentieth normal alkali and a hundred cubic centimeter burette. 

 The latter was of the bore of the ordinary fifty cubic centi- 

 meter burette but was made with a top bulb that brought its 

 capacity up to a hundred cubic centimeters. When twenty- 

 five cubic centimeter portions of the reacting mixture were 

 titrated with this it was possible to have a total range of from 

 ten to fifteen cubic centimeters with a very slight increase in 

 the error. One drop of twentieth normal alkali was sufficient 

 to produce a perfectly definite color change in the indicator, and 

 there was little increase of error due to the draining and read- 

 ing of this burette. 



The procedure may be briefly summarized as follows : Two 

 hundred and fifty cubic centimeter flasks containing the solu- 

 tions of the esters in decinormal hydrochloric acid were placed 

 in an accurately regulated thermostat.^ At measured intervals 

 of time portions were removed by means of a twenty-five cubic 

 centimeter pipette, run into cold water and their acidity deter- 

 mined by titration with twentieth normal barium hydroxide 

 solution. Phenolphthalein was employed as an indicator. 



Of the more insoluble esters, saturated solutions were pre- 

 pared by shaking the acid vigorously with an excess of ester 

 and then filtering. The paper was first moistened with the 

 acid solution, which prevented the passage through it of any of 

 the undissolved ester. The measurements of the final acidity 

 were made upon portions ef the mixtures, heated several days 



*Zeitschr. f. phys. Chem., xiii, 561. 

 f This Journal, xxx, 72. 



