578 PROCEEDINGS OF THE AMERICAN ACADEMY. 



of the pyrosulphuryl chloride, especially if the preparation had been 

 allowed to stand some time, in one case three summer months. This 

 excess may be formed by the following reaction : 



SizOCle + 6SO3 = 2Si02 + 3S2O5CI2 (2) 



as a considerable amount of silica is deposited during the standing. 



It follows from our work that the reaction constructed by Dammer 

 on Gustavson's meagre statement 



4SO3 + SiCl4 = 2S2O5CI2 + SiOa 



is incorrect, inasmuch as there is formed at first the oxychloride : 



2SO3 + 2SiCl4 = S2O5CI2 + SioOCle (1) 



and only by a secondary reaction, silica, 



SiaOCle + 6SO3 = 2Si02 + 3S2O5 Clo 



By combining the two reactions that given by Dammer is indeed 

 obtained, but (2) takes place only to a limited extent and always 

 follows (1). To give Dammer's equation alone would be misleading; 

 the two separate equations (1) and (2) must be given and explained. 



There is some evidence that the distillate contains a loose compound 

 of pyrosulphuryl chloride, S0O5CI0, and silicon oxychloride, SisOCle, 

 formed under the influence of heat. The distillate did not freeze 

 unaided above —78°, except in a single case, while a mixture of equal 

 parts of the two substances crystallized easily on cooling and melted 

 at —40° to —38°. It is astonishing that this mixture melted at about 

 the same temperature as its constituents, S2O5CI2, melting at —37°, 

 Si20Cl6 at —40°. A mixture of 15.6 grams of S2O5CI2 with 5.2 grams 

 Si20Cl6, which therefore had about the same composition as one of our 

 distillates crystallizing at — 78°, was divided into two parts, one of which 

 was heated for 5 minutes in the Bunsen flame; on cooling the two in 

 the carbon dioxide-alcohol mixture, the portion which had been heated 

 took 20 times as long to begin to solidify as the unheated one. This 

 could hardly be accounted for unless the supposition was made that 

 the two substances had combined under the influence of heat. The 

 assumption of such a compound does not interfere with the other ob- 

 servations made, thus the boiling point might remain that of mixed 

 silicon oxychloride and pyrosulphuryl chloride, because the compound 

 between the two is too weak to exist in the state of vapor, a recombina- 

 tion, however, taking place as they return to the liquid phase; the 

 formation by distillation of nearly pure pyrosulphuryl chloride took 

 place only when the temperature was raised much higher than usual. 



