706 PROCEEDINGS OF THE AMERICAN ACADEMY. 



complete dissociation is undoubted. Whether we shall ascribe the for- 

 mation of the last two of these bodies to reactions (1) and (3) or to 

 reactions (2) and (4) is immaterial. But it is not unreasonable to 

 suppose that reaction (1), which at diminished pressure and compara- 

 tively low temperature is predominant over reaction (2), becomes not 

 only secondary to reaction (-2) at atmospheric pressure and higher 

 temperature, but also that, at the highest temperatures noted, it 

 would merge into reaction (5). 



Whatever may be the mechanism of this rather complex dissociation, 

 it is certain that distillation of chlorsulphonic acid at any pressure will 

 result in a product which may contain, in varying amounts, sulphuryl 

 chloride, chlorine, sulphur dioxide, sulphur trioxide, hydrochloric acid, 

 and sulphuric acid. The disagreeing results of previous observers on 

 the constants of chlorsulphonic acid are therefore easily explained, 

 for their products, though often of sufficiently good quality for practi- 

 cal purposes, were contaminated by more or less of these dissocia- 

 tion products, and hence showed varying boiling points, specific 

 gravities, etc. 



By distillation with hydrochloric acid, reaction (1) obviously runs to 

 the left, and there should be little tendency to dissociation. Ordinary 

 distillation, at atmospheric or low pressure, will not purify. After 

 realization of this fact, we turned to crystallization, as will be shown. 



Behavior of Chlorsulphonic Acid under Distillation. — In Prepara- 

 tions 10 and 11 above, in which the distillation was without hydro- 

 chloric acid, the product is contaminated by the products of dissociation, 

 and the apparent yield is less. In the others, there is a greater or less 

 amount of hydrochloric acid present and probably less of the dissocia- 

 tion products. 



The crude preparations of chlorsulphonic acid showed a very charac- 

 teristic behavior on cooling. At —70° to —80°, the liquid becomes 

 thicker and gradually viscous as the temperature falls. At —130° to 

 —140° an amorphous, vitreous mass is formed, which under rising 

 temperature becomes gradually viscous again from —140° to —120°, 

 averaging, say, at —130°, and is limpid at about —85°. This behavior 

 differentiates the substance sharply from pyrosulphuryl chloride, which 

 gave definite crystals at —40° to —35°, and at —70° to —60° even when 

 containing 90 per cent of chlorsulphonic acid. But, while the differen- 

 tiation was clear, the melting evidently indicated impure chlorsul- 

 phonic acid. 



Preparation 11 became viscous at —133-127°. At 24-27 mm. it 

 boiled chiefly at 80-82°, and the solidified product softened at —125- 

 117°. The specific gravity was 1.786 at 20°. To avoid the presence 



