692 PROCEEDINGS OF THE AMERICAN ACADEMY. 



sodic hydroxide being interposed as a precaution against corrosion by 

 the acid vapors. The flask containing the reaction mixture is closed 

 by a rubber stopper carrying a thermometer, and is about three- 

 quarters immersed in an oil bath, the temperature of which is con- 

 trolled by a second thermometer. The suction is applied until the 

 hydrochloric acid is drawn off, and the oil bath is then gradually 

 heated. The pyrosulphuryl chloride in the mixture distils with little 

 or no decomposition, leaving the sodic chlorsulphonate as a dry mass. 

 The oil bath, as distillation slackens, is kept for some time at a some- 

 what higher temperature than the boiling point of the pyrosulphuryl 

 chloride, but a considerable amount of the latter adheres to the 

 residue. 



The product thus obtained melts after solidification within a few de- 

 grees of the proper point, and a single rectification over a small quantity 

 of fused sodic chloride under diminished pressure is usually sufiicient to 

 give a perfectly pure product. 



Regeneration of the Chlorsulphonic Acid. — We at first thought that 

 it would be practicable to recover from the sodium salt residue the 

 chlorsulphonic acid of the original reaction product, — even perhaps to 

 use the Schiitzenberger method for the preparation of both bodies by 

 employing an oleum of suitable strength. While by distillation of the 

 residue with excess of fuming sulphuric acid according to the equation 



SOsNaCl + H2S2O7 = SO3HCI -f NaHSaO, " 



the chlorsulphonic acid is indeed regenerated, it is in an impure state 

 and its purification is not worth while, since a pure product is so easily 

 obtained by the Williamson method. 



The Properties of Pyrosulphuryl Chloride. 



Pyrosulphuryl chloride is a colorless liquid, fuming slightly in moist 

 air and becoming turbid when added to a small amount of water. It 

 sinks in water as an oil, gradually decomposing into chlorsulphonic acid, 

 which in turn gives sulphuric and hydrochloric acids as final products. 

 Chlorine and probably sulphur dioxide may be formed in small amount. 

 It boils at 152.5° to 153° at 766 mm., and is not appreciably dissociated 

 at this temperature, if perfectly dry, but complete absence of moisture 

 is difficult to secure, as the substance is very hygroscopic. At a pres- 



"' We do not assume the formation of such a salt, though it is supposed 

 to exist (e. g., Schultz-Sellac, Ber., 4, 109 (1871)). The reaction is, however, 

 more complete when the fuming sulphuric acid is in this proportion. 



