SANGER-RIEGEL. — SULPHUR TRIOXIDE-SILICON CHLORIDE. 579 



SO that the compound would be decomposed, the silicon oxychloride 

 disappearing completely as such, leaving the pyrosulphuryl chloride; 

 again the reaction of water on such a compound might well be a de- 

 composition into the components accompanied by the destruction of 

 the silicon oxychloride, leaving a part at least of the pyrosulphuryl 

 chloride to react more slowl}^ for it is less sensitive to water than the 

 oxychloride, as shown quantitatively further on. It must ba added, 

 however, that all the distillate which gave distinctly the oily deposit 

 with water were low in silicon, and contained an excess of pyro- 

 sulphuryl chloride, so that all of the combined oxychloride and pyro- 

 sulphuryl chloride might have been destroyed, leaving only the free 

 pyrosulphuryl chloride to become visible. The assumption of this 

 compound explains to perfection why the distillates nearing in percent- 

 age composition an equi-molecular mixture of the two substances did 

 not crystallize even after seeding with pyrosulphuryl chloride, while 

 the distillates low in silicon, containing an excess of pyrosulphuryl 

 chloride, which could exist free, crystallized readily under the same 

 conditions. Reaction (2) is not affected by this assumption, for it 

 takes place on standing at room temperature, or at the most at 50°, so 

 that the loose compound, for which we assume that a temperature of 

 about 130° is needed, is not formed. Our effort, however, was to 

 prove reactions (1) and (2) rather than study this subsequent com- 

 pound. 



EXPERIMENTAL PART. 



Materials: The commercial sulphur trioxide marked C. P. contained' 

 no impurities. In order to obtain a liquid at room temperature it 

 was melted for some experiments, for others the melted substance was 

 added to fuming sulphuric acid in the proportions necessary to give 

 solutions of various strengths which were ascertained by titration or 

 gravimetrically. The melting was done in a cylindrical copper air 

 bath built for the purpose, and this was extraordinarily easy with a 

 fresh sample;^ a moderate temperature was required (about 50° in 

 bath), the melting was rapid, no clots formed in the center, and the 

 low temperature caused little boiling, hence little pressure, so that the 

 stopper could be left in place without danger; with an old sample on 

 the other hand the melting was almost impossible; so much heat was 



5 Fresh sulphur trioxide melts at 17.7°; old samples do not melt at all, 

 but sublime; Knietsch, Ber., 34, 4101 (1901). Compare also Schenck, Lieb. 

 Ann. 316, 1 (1901); Weber, Ber., 19, 3187 (1886). 



