694 PROCEEDINGS OF THE AMERICAN ACADEMY. 



be boiled without partial dissociation, but, when equilibrium sets in, the 

 boiling point is about 151-152° at 765 mm. The slight dissociation is 

 partly into hydrochloric acid and sulphur trioxide (which react partially 

 to form water, sulphur dioxide, and chlorine); partly to sulphuryl chloride 

 and sulphuric acid. The latter dissociation may be brought about at 

 the boiling point by a catalyser. At a pressure of 19 mm. it boils at 

 74-75°, but the dissociation into hydrochloric acid and sulphur trioxide 

 is increased ; still more at from 2 to 4 mm., the boiling point being then 

 approximately 60-64°. At the boiling point of aniline, the dissociation, 

 though not complete, amounts to about two volumes. It crystallizes 

 readily at low temperature and melts at —81° to —80°. The crude acid 

 requires a lower temperature for solidification, changing into a vitreous 

 body, which becomes viscous at about —130° to 125° and sometimes partly 

 crystalline. The specific gravity at 20°, referred to water at 4°, is 1.753 ; 

 at 0° (water at 4°), 1.784. With finely divided tellurium, chlorsulphonic 

 acid gives a cherry-red color, which persists for several hours, fading 

 gradually to purple, then pink, and becoming finally colorless. With 

 finely divided selenium, it gives a moss green color, which gradually 

 becomes a fainter green, then yellow, and finally colorless. 



For the properties of mixtures of chlorsulphonic acid and pyrosul- 

 phuryl chloride, see page 712 and Table III (page 713). 



Experimental. 

 Preparations of Pyrosulphuryl Chloride. 



1. 105 g. oleum (90 per cent SO3) were added to 110 g. CCU (10 

 per cent over theory) in an hour. 22 g. distillate were obtained up to 

 130°; 83 g. from 130° to 155° (chiefly 150-152°), and the residue was 

 less than 2 g. The main fraction melted at —128° and was chiefly 

 chlorsulphonic acid. This was treated with 50 g. fused sodic chloride 

 and distilled, a U-tube *** in liquid air being placed after the receiver. 

 9 g. distillate were obtained from 53° to 60° (26 mm.); the U-tube con- 

 tained a little hydrochloric acid. The melting point of the distillate, 

 —39°, showed a fairly pure pyrosulphuryl chloride. The dry residue 

 was treated with 125 g. oleum (91 per cent SO3) and distilled, a bottle 

 cooled by ice and salt being placed before the U-tube in liquid air. At 

 78-87° (23 mm.) 46 g. of distillate were obtained, melting at —128-125°, 

 s. g. 1.767 at 20°. In the cooled bottle was a little sulphur trioxide, 

 in the U-tube a little hydrochloric acid. 



The yield of chlorsulphonic acid is low owing to insufficient carbon 



" Figure 1, p. 697. 



