SANGER-RIEGEL. — PYROSULPH. CHLORIDE-CHLORSULPH. ACID. 691 



oleum, the heating is continued for some time after the evolution 

 stops. The proportion of carbon tetrachloride to oleum should be 

 about two to one. 



As a partly solid oleum or " anhydrous " sulphur trioxide is less 

 easy to handle, we have preferred to use as strong a mixture as will 

 remain liquid at ordinary temperature,^® though the yield of pyrosul- 

 phuryl chloride is less. If one wishes to use- the stronger reagent, 

 however, the apparatus may be so modified that the top of the con- 

 denser tube is sealed and the* separating funnel containing the melted 

 trioxide is connected directly with the flask by means of a two-holed 

 rubber stopper, through the second hole of which passes the con- 

 denser tube instead of being sealed to the flask. Without this arrange- 

 ment the melted substance would solidify in passing through the 

 con denser. SI 



The contents of the flask are transferred to a distilling flask and 

 fractioned ; the first portion, up to 120° or 130° containing a little 

 phosgene and excess of carbon tetrachloride, being rejected. The 

 second fraction, which may run to 160°, is best redistilled and that 

 portion boiling above 130° submitted to the following separation : — 

 The mixture is placed in a roomy distilling flask, cooled by ice, and 

 treated with small portions of fused, powdered sodic chloride, dried 

 before use by heating to ca. 150° and cooled in a closed bottle. The 

 amount necessary is calculated from the amount of water in the oleum 

 and hence the probable quantity of chlorsulphonic acid present. From 

 ten to twenty per cent in excess of that called, for by the following 

 equation is necessary. 



SO3HCI + NaCl = SOsNaCl " + HCl. 



When the evolution of hydrochloric acid has ceased, and this may be 

 promoted at the end by gentle warming, the pasty or partly dry mass 

 is distilled under about 20 or 30 mm. pressure. For this purpose we 

 extend the side-tube of the flask by sealing on a tube of about 50 cm., 

 which is then surrounded by a short condenser jacket. Over the end 

 of the lengthened side-tube is slipped a distilling flask of suitable size, 

 fastened by a rubber stopper so that the end of the tube dips into the 

 belly of the flask. The side-tube of the receiver is connected with the 

 exhaust and manometer ; a system of absorption tubes filled with stick 



60 From 92.5 to 95 per cent total SO3. 

 ^^ See also Preparation 6, p. 696. 



^* For the preparation and analysis of sodic chlorsulphonate, see Ruff 

 (note 45, p. 681). 



