184 Prof. Magims on Red and Black Sulphur. 



dently depends upon the state of aggregation, for even i*ed sul- 

 phur, when finely powdered, appears yellow-red. 



But this yellow-red powder, even should it appear quite yel- 

 low, raay be easily distinguished from the yellow insoluble sul- 

 phur by fusing at 110° to 130° C, when, on cooling, it will 

 form quite red masses; or by fusing at 300° C. and cooling 

 quickly, when it will be converted into* black sulphur ; in short, 

 it will possess all the properties of red sulphur. 



Insoluble red sulphur, whether it be quite red or yellowish, 

 remains unchanged on keeping. At least I have preserved spe- 

 cimens of it, of several different tints, for many months without 

 observing any change. A mixture of much red and little yellow 

 sulphur, however, changes its colour gradually from red to yellow. 



Even in solution red sulphur suffers this change. A deep red 

 solution was preseiTed in a well-closed flask ; its redness conti- 

 nually decreased in intensity until, in two months, it appeared 

 orange. Whether this change was caused by the heat of the 

 sun, to which the solution was sometimes exposed, or whether it 

 proceeded in darkness also, I must leave undecided. 



As Pasteur and Deville have already shown*, prismatic crystals 

 are formed in a concentrated solution of red sulphur with 

 little yellow, which at first are red, but after some time yellow 

 and opake. I have found that of these, many are only partially 

 soluble in bisulphide of carbon. The insoluble yellow residue 

 often retains a prismatic form, but deports itself like red sulphur. 



But, inasmuch as red sulphur possesses no crystalline struc- 

 ture, the prismatic form evidently belongs to the yellow sulphur, 

 which, as Deville has already shown f, can assume that form at 

 the usual temperature if crystallized from certain solvents, and 

 which, when crystallized from bisulphide of carbon, apparently 

 assumes that form only because red sulphur is at the same time 

 present in the solution. It is certainly remarkable that a body 

 at the same temperature crystallizes in two different systems, 

 though we know that with certain salts, e. g. alum, certain sur- 

 faces are principally formed when the solution is acid, and others 

 when it is basic. But when, by the presence of a foreign sub- 

 stance which does not at all enter into the crystals, the relations 

 of cohesion become altogether changed, it is possible that this 

 change may be so great that the crystals form themselves accord- 

 ing to a quite different system. This is especially conceivable in 

 sulphur, which in every case passes so easily from one system 

 to another. 



When red sulphur is exposed for some time to a temperature 

 of 100° C, it becomes converted into soluble yellow sulphur. 



* Comptes Rejidus de V Academic des Sciences, vol. xxvi. pp.48, 117. 

 t Ibid. vol. xxxiv. p. 634. 



