248 BAXTER, WEATHERILL AND SCRIPTURE. 



excess of ammonia was removed by wash bottles containing dilute 

 sulfuric acid. Hydrogen resulting from catalytic decomposition of 

 the ammonia was next burned with hot copper oxide, and the gas was 

 then purified and dried by silver nitrate solution, sodium hydroxide, 

 concentrated sulfuric acid and phosphorus pentoxide. Finally last 

 traces of oxygen were absorbed by hot copper oxide. The apparatus, 

 which was constructed entirely of glass, is described in detail by 

 Baxter and Grover. 15 



The Preparation of Silicon Tetrachloride. 



The silicon tetrachloride was prepared by the action of chlorine on 

 silicon, and was purified by distillation in exhausted glass vessels 

 without exposure to air or moisture. Moisture was particularly to be 

 avoided because of the decomposition products resulting from hy- 

 drolysis, i.e., silicic acid, silicon oxychlorides and hydrochloric acid. 

 Because in preparing the chloride it was impossible entirely to avoid 

 exposure to moist air, the process of purification was adapted for the 

 removal of these impurities. In addition to the above impurities, the 

 following were to be expected and provided for: silicon hexachloride 

 and octachloride, titanium tetrachloride and carbon tetrachloride, the 

 last two resulting from impurities of carbon and titanium in the silicon. 

 Fortunately the boiling points of all the impurities are sufficiently far 

 removed from that of silicon tetrachloride to lead to the expectation 

 that they would be readily removed by fractional distillation. So far 

 as can be told this proved to be the case. In the following table are 

 given the boiling points of the impurities in question. 



Several specimens of the tetrachloride were prepared, differing chiefly 

 in the method and extent of the fractionation. One lot was purchased 

 from the General Electric Company. This had been made from 

 silicon and chlorine, and had been rectified. Our own preparations 

 were made as follows : Dry chlorine was passed over silicon in a hard 

 glass tube heated to redness, and the product was condensed. The 

 chlorine was drawn from a large tank which served for all the prepara- 



15 Baxter and Grover, Jour. Amer. Chem. Soc, 37, 1037 (1915). 



