M. Wurtz on Chloride of Thionyle. 387 



Wurtz has succeeded in obtaining chloride of thionyle by the 

 direct action of anhydrous hypochlorous acid on sulphur, 



C1 2 G + S=SQC1 2 . 



Hypochlorous 

 acid. 



Gaseous hypochlorous acid was passed into subchloride of sul- 

 phur holding sulphur in solution, and the operation interrupted 

 when the whole of the latter had disappeared. The chloride of 

 thionyle, which boils at 78°, could be separated by fractional 

 distillation from the subchloride of sulphur, which boils at 

 139° C. 



It is a colourless liquid, of an irritating odour ; its density at 

 0° is 1*675. Thrown into water, it at first falls to the bottom, 

 and is then rapidly decomposed, just as is terchloride of phos- 

 phorus. The reaction is expressed by the equation 



S0C1 2 + H 2 = 2HC1+S0 2 . 

 If, instead of diffusing the sulphur in an inert liquid like the 

 subchloride, which must be cooled to 10° during the operation, 

 the sulphur be projected into liquefied anhydrous hypochlorous 

 acid, an explosion ensues. 



In what are called abnormal vapour-densities it is assumed 

 that a decomposition of the bodies takes place ; and Deville has 

 endeavoured to effect this decomposition in a visible manner*. 

 If pentachloride of phosphorus is heated in a closed tube in the 

 oil -bath, and is thereby decomposed into PCI 3 and CI 2 , the green 

 colour of the gas must become visible. In order to show this, 

 Deville filled two perfectly equal glass tubes, one with a mixture 

 of equal volumes of chlorine and air, and the other with some 

 pentachloride of phosphorus. Both were heated in the oil-bath ; 

 the tubes only projected to a small extent from the bath, so that 

 a layer of gas 3 to 4 decimetres in thickness could be perceived. 

 Prom a certain range of temperature onwards, the tube with the 

 PCI 5 is seen to be continually greener until it exhibits the same 

 colour as the tube containing air and chlorine; but as long as 

 the perchloride remains colourless, no decomposition takes place. 

 Only then does dissociation occur ; and from the known vapour- 

 densities the tension of dissociation can be calculated. 



A similar deportment is exhibited by the vapour of iodide of 

 mercury. If this body be heated in a flask or retort above its 

 melting-point, at a certain stage violet vapours are observed on 

 the sides of the flask, which disappear in the interior of the ves- 

 sel — that is, in the colder part. Here occurs, therefore, a recom- 

 bination of the separated iodide. As a volume of iodine vapour 

 and air equal in volume to this vapour exhibits a far more in- 

 tense colour, the author assumes that at this temperature iodide- 

 * Comptes Rendus, vol. lxii. p. 1157. 



2C2 



