ATOMIC WEIGHT OF SILICON. 



255 



water pump, through a drying tube containing sodium hydroxide. 

 The tetrachloride was allowed to boil vigorously for a short time, until 

 several cubic centimeters had evaporated, together, we hoped, with 

 much of the hydrochloric acid formed by exposure to the moisture of 

 the air. Repeated distillation was then carried out with apparatus 

 similar to that indicated in Figure 5. The Hempel column was cooled 

 with ice and water, while the receiver was chilled with carbon dioxide- 

 alcohol mixture. A continuous reflux action was evident in the Hempel 

 column throughout the distillation. In each distillation a few cubic 

 centimeters of residue were rejected. Furthermore, frequently at the 

 end of a distillation the temperatures of still and receiver were re- 



Figure 5. 



reversed so that the most volatile material was largely condensed in 

 the still. Sometimes the same effect was produced by inserting an 

 additional large bulb in the train and condensing the most volatile 

 material in this bulb before the next distillation. 



After six distillations, one of the capillary connections in the ap- 

 paratus was accidentally broken so that moist air was admitted. 

 With as little exposure to the air as possible the chloride was intro- 

 duced into bulb // and seven more distillations were carried out in the 

 same way. In the last distillation the two most volatile fractions 

 (1 and 2, Fig. 4) were collected for analysis, the main bulk of material 

 was distilled into bulb from bulb A, and the residue was collected in 

 bulbs 14 and 15 for analysis. 



Since the possibility of the existence of constant boiling distillates 

 is always to be feared in fractional distillation, an effort was made to 

 avoid or detect the effect of such a mixture by further distillation at a 

 different pressure. To do this the still was immersed in warm water, 

 the Hempel column was kept at about 5° and the receiver was sur- 



