Drxishel and Hill — Esters of Halogen Substituted Acids. 75 



two tubes are sealed. These curve downward for about six 

 inches, then upward above the top of the toluol bulb, the 

 downward portion consisting of 8""" glass tubing and the 

 upward portion of heavy capillary tubing. To the upper end of 

 one of the capillary tubes is sealed a glass-stoppered bulb hav- 

 ing a stopcock. A platinum wire is sealed into the other 

 above the level of the water in the thermostat. To the upper 

 end of this capillary tube is sealed an enlarged tube closed 

 with a two-holed rubber stopper carrying an adjustable elec- 

 trode terminating in a platinum wire. These electrodes are 

 connected with a gas regulator of the Hahn type.* Mercury 

 fills both capillaries and a portion of each of the larger tubes 

 connecting the capillaries with the toliiol bulb, the mercury 

 columns being so adjusted that their weights balance each 

 other, thereby preventing leakage of toluol at the stopcock. 

 The tube with the adjustable electrode is filled with alcohol to 

 prevent sparking. When it is desired to change the tempera- 

 ture of the thermostat, all that is necessary to set the thermo- 

 regulator is to open the stopcock of the bulb to allow the 

 toluol to pass through and close it again when the proper 

 temperature is reached. The final adjustment is made by 

 raising or lowering the electrode by turning the screw. A 

 Beckmann's thermometer, graduated to 0"01°, is set and clamped 

 in the thermostat to indicate the temperature. Stirring is 

 effected by means of a two-flanged stirrer mounted on ball- 

 bearings and driven by a low speed motor, which is in series 

 with the gas regulator and in parallel with a resistance. 

 Rotary stirring is prevented by a rectangular copper plate 

 fixed near the bottom of the thermostat and so placed as to 

 direct the current upwards. The temperature can be main- 

 tained constant within ±0'01° C. 



Procedure. — In the case of the esters readily soluble in lSr/20 

 acid the amount required to make up a N/20 solution was 

 weighed out in a small flask and dissolved in 250'^"'' of the 

 acid used which had previously been warmed in the thermo- 

 stat to the temperature at which we were working. The 

 mixture was then poured into pressure flasks and these were 

 submerged in the thermostat to within an inch of their mouths. 

 At first Erlenmeyer flasks of about 500™'' capacity were used, 

 but there was always more or less variation in concentration 

 due to evaporation into the space above the solution and 

 condensation on the colder upper surfaces of the flask. The 

 smaller flasks had less vacant space and being well submerged 

 condensation was prevented to a great extent. 



At regular intervals a 25™' portion of the reaction mixture 

 was withdrawn with a pipette and run into about lOO'^'"' of 

 *Zeitschr. phys. Chem., xliv, 525. 



