576 PROCEEDINGS OF THE AMERICAN ACADEMY. 



moist air and reacts violently with water; it contains sulphur, 

 chlorine, silicon, and oxygen, and the indefiniteness of its boiling point 

 indicates that it is a mixture. We have not succeeded in isolating the 

 substances of which it is composed, although we tried every way we 

 could devise. Nevertheless we are convinced that it is made up of 

 pyrosulphuryl chloride S2O5CI2 and silicon oxychloride Si20Cl6, because 

 all our complete analyses of well-established specimens give percent- 

 ages corresponding to such a mixture; that is, if the amount of sulphur 

 found is assumed to be present as pyrosulphuryl chloride, and the 

 amount of chlorine corresponding to the sulphur in that compound is 

 calculated, the difference between the total chlorine and this amount 

 agrees well with the chlorine necessary to form silicon oxychloride with 

 the silicon found; thus out of 18 analyses, it agrees in 8 cases within 

 1 percent, in 5 other cases within 2 percent, in one more case within 

 2.5 percent. The four remaining analyses gave results which did not 

 agree, but this is satisfactorily explained, for these are analyses of frac- 

 tions boiling at higher temperatures than the usual one, namely above 

 150°, indicating the presence of other substances. These analytical re- 

 sults are confirmed by other observations. A specimen distilled from 

 a heavy gelatinous residue of silicic acid gave results on analysis differ- 

 ing by only 1.8 percent on the sulphur, and 4 percent on the chlorine 

 from pyrosulphuryl chloride, showing that that substance had been 

 formed; another distilled from a large excess of phosphorus pentoxide, 

 melted at —40° to —50° and crystallized in radiating crystals like pyro- 

 sulphuryl chloride which melts at — 37°, showing its presence again; 

 a third, distilled from an excess of sodium chloride gave analytical 

 results indicating a more impure pyrosulphuryl chloride. It seems 

 therefore that heating the liquid with a large excess of any solid dis- 

 poses of most of the silicon oxychloride, but reveals the presence of the 

 pyrosulphuryl chloride. 



The boihng point of the distillate, 135-150°, is what would be ex- 

 pected of a mixture of pyrosulphuryl chloride and silicon oxychloride, 

 for the former boils at 152.5°-153°, and its boiling-point may be low- 

 ered 5-10° by a minute amount of water, and the latter boils at 136- 

 139°. The boiling-point of the mixture is not changed by the addition 

 of one fifth of its weight of pyrosulphuryl chloride. If a great deal of 

 water is added to the original distillate a violent reaction attended with 

 the formation of silicic acid takes place such as would be expected from 

 silicon oxychloride and a heavy liquid separates at the bottom of the 

 vessel, dissolving but slowly. This is the behavior of pyrosulphuryl 

 chloride or of sulphuryl chloride, but the latter is excluded by the 



