680 PEOCEEDINGS OF THE AMERICAN ACADEMY. 



needed that the small quantity which had melted boiled away before 

 any more became liquid. 



Silicon tetrachloride was prepared by passing dry chlorine over 

 powdered silicon spread out in a hard glass tube, and heated in a com- 

 bustion furnace.^ An adapter at the end of the tube (the latter was 

 slightly inclined towards the former) fitting into a receiver set in ice, 

 completed the apparatus. Charges of 50 grams yielded 190 to 225 

 grams of silicon tetrachloride, that is, 64 to 75 percent of the theo- 

 retical yield. Special effort to obtain a large yield was never made; 

 on the contrary economy of time was the only consideration. In 

 this respect this method is ideal; the apparatus could be set up in a 

 few minutes, and a preparation carried through in an afternoon.^ 

 The silicon contained iron, which caused the presence of ferric chloride 

 in the crude product; the latter also contained free chlorine. The 

 crude product was freed from chlorine by shaking with mercury and 

 was then distilled.^ It was kept in glass stoppered bottles under a 

 dry bell-jar, or the flasks were sealed off. The bottles were left in the 

 open at first, but the moist air caused a deposit of silica which cemented 

 the stopper in place, and such a bottle could only be opened by break- 

 ing it, when it usually exploded. Rubber stoppers were found more 

 satisfactory, but these hardened in time and also became cemented. 

 Bottles nearly empty and imperfectly closed to moisture exploded 

 spontaneously, because of the formation of hydrochloric acid. 



Silicon oxychloride was prepared by the method of Troost and 

 Hautefeuille^, namely, by passing a mixture of chlorine and oxygen 

 over heated metallic silicon in the same apparatus as the one used for 

 silicon tetrachloride. The yield was very small; out of 154 grams a 



6 Hempel and Haasy state that thev used this method, but give no details. 

 Zeitschr. anorg. Chem., 23, 32 (1900)" 



7 In our earlier work the silicon tetrachloride was made by passing chlorine 

 over silicide of copper as done by G. H. Pratt (M. I. T. thesis, 1897, vol. 68; 

 in the hands of Vigouroux, C. R., 129, 334 (1899), this method did not give 

 satisfactory results) except that glass retorts were used instead of iron tubes, 

 but this method was much slower, less convenient, and gave a poor yield. 



8 The melting point of silicon tetrachloride is —69° (corr.) It was deter- 

 mined several times on different samples, by the beaker method (see note 11) 

 and by complete immersion of the thermometer. W. Becker and J. Meyer 

 (Zeitschr. anorg. Chem. 43,251 (1905)) give this point as — 89°; they determined 

 it by winding a thermo-element on the outside of the containing vessel, while 

 this was suspended in a Dewar tube containing a little liquid air; the junction 

 was presumably at the bottom of the containing tube. Their material was 

 exceedingly pure, but the method used in obtaining the melting-point is open 

 to objection. 



9 Bull. Soc. Chim., 35, 360 (1881). 



