400 Prof. R. Weber on a new Oxide of Sulphur and an 



W. Stein* agreed with Berzelius in regarding the blue 

 substance produced from sulphur and anhydride as a solution 

 of the former in the latter. The blue colour he believed to 

 be due to the extremely finely divided state in which he sup- 

 posed the sulphur to be present. 



Preparation of the Blue Sulphur Compound. 



The isolation of this compound is rendered possible by the 

 fact that it is not soluble in perfectly pure sulphuric anhy- 

 dride (prepared by careful distillation of the liquid which is 

 obtained by gently warming oil of vitriol), and that any excess 

 of anhydride may therefore be removed. Inasmuch as the 

 compound is stable for some time at a temperature of 10° or 

 15°, exact quantities of it may be weighed out for analysis. 

 It is only by using pure anhydride that the blue sulphur 

 compound can be obtained in definite shape ; ordinary sul- 

 phuric anhydride (as will be shown in a subsequent commu- 

 nication) is not pure. 



When sulphuric anhydride, prepared without especial 

 precaution, and therefore containing a small quantity of the 

 hydrate, is brought into contact with sulphur, the blue com- 

 pound is dissolved as quickly as it is formed in the excess of 

 (impure) anhydride, from which it cannot be separated. A 

 portion of the blue substance solidifies along with the anhy- 

 dride, which is thereby more or less deeply coloured. 



If perfectly dry powdered sulphur be added in successive 

 small quantities to pure anhydride, the blue compound sepa- 

 rates in the form of small drops, which, being heavier than 

 the anhydride, settle to the bottom of the vessel and there 

 solidify. For the proper carrying out of this operation it is 

 essential that the temperature be about 15°, inasmuch as 

 decomposition of the compound readily takes place at higher 

 temperatures, while at temperatures under 15° the anhydride 

 solidifies. In the solidification of the blue compound heat is 

 evolved sufficient to bring about partial decomposition, unless 

 the temperature be maintained at a sufficiently low point. 



In order to prepare pure sulphuric anhydride, the substance 

 obtained by heating fuming oil of vitriol is carefully distilled 

 at as low a temperature as possible ; the first portions of the 

 distillate are rejected, and those which succeed are collected 

 in a receiver which fits closely to the neck of the retort, and 

 which is maintained at a temperature of about 15° ; care being 

 taken that the distillate does not solidify. 



In order to prepare the blue compound, small quantities of 



* J. fur prakt. Chem, vol. vi. p. 172. 



