594 PROCEEDINGS OF THE AMERICAN ACADEMY. 



important to add that once the higher boiling fraction was remo\ed 

 from the excess of sulphur trioxide, or which is the same, from the 

 low-boiling fraction, no solid was deposited. 



Most of the mixtures of pyrosulphur^l chloride and silicon oxy- 

 chloride obtained by us crystallized at various temperatures, the high- 

 est one being —60°, the lowest —78°; some of them did not crystallize, 

 but merely solidified to a vitreous mass, near —120°. Pyrosulphuryl 

 chloride melts at —37°, silicon oxvchloride near —40°. A mixture of 

 equal parts of the prepared pure substances melted at —40° to —38°, 

 but on mixing 15.6 grams of the former with 5.2 grams of the latter, 

 and heating half of the mixture on the Bunsen flame, it was found that 

 the heated portion took twenty times longer to crystallize than the 

 unheated one. As stated in the introduction, the only possible expla- 

 nation is that the two substances form a compound under the influence 

 of heat. All the mixtures were obtained by means of one or more 

 distillations, and submitted to the heat of a flame, and this influence 

 of heat explains the phenomena of crystallization observed. In the 

 mixtures containing approximately one molecule of each substance, 

 the two substances are combined, and not being free, cannot crystallize 

 when a seed of either substance is introduced ; in the mixtures contain- 

 ing an excess of pyrosulphuryl chloride, the silicon oxychloride is all 

 combined, but some of the pyrosulphuryl chloride remains free, hence 

 this mixture can crystallize on a seed of pyrosulphuryl chloride, al- 

 though here again, it will not crystallize on a seed of the oxychloride. 



The deposit formed on standing over the summer was placed in a 

 Gooch crucible, washed twice with silicon tetrachloride, pressing down 

 the material with a glass rod, and using a suction pump to remove all 

 the liquid : all as rapidly as possible. The solid was then packed and 

 sealed in tubes, in which it remained without alteration. This material 

 appears perfectly dry; it smokes strongly in the air and attracts mois- 

 ture rapidly. With water it reacts violently; a few bubbles of gas 

 escape, and a slight yellow color (due to chlorine) develops ; the white 

 particles become transparent, but retain their original shape; no 

 visible amount of silica separates out from the liquid. The reaction 

 with dilute sodium hydroxide is the same, but more violent. When 

 moistened with chloroform the solid becomes translucent and filled 

 with bubbles. Heated over the flame it evolves white fumes, and 

 leaves behind a white ash, which no longer reacts Avith water. The 

 deposit is not homogeneous; the silicon percentage varied between 

 6 and 10; the portions which had been formed against the wall of the 

 flask contained the higher percentage. One sample contained: 



