Prof. Magnus on Red and Black Sulphur. 1 81 



comes insoluble, and that it may be sublimated without residue, 

 we may conclude that it does not owe its colour to the quantity 

 of carbon it contains. In order to render this certain in another 

 manner, chlorine was conducted over black sulphur which had 

 been prepared from red. After distilling over the chloride of 

 sulphur, a residue remained which amounted to scarcely one- 

 tenth per cent., and this arose evidently from dust which had 

 become mixed with the red sulphur. 



The manner in which black sulphur is obtained is very remark- 

 able, for it is apparently formed only by repeated sudden cool- 

 ings of common sulphur. By heating for a long time at several 

 different temperatures it was not possible to obtain it, even 

 when the temperature of fusion was raised to near the boiling- 

 point of sulphur*. Once or twice only, and that in a manner 

 scarcely explicable, I obtained red-brown sulphur, quite similar 

 to remelted sulphur, at the first cooling after the common sul- 

 phur had been heated for a short time. 



It would appear as if, sometimes, the sulphur of commerce, 

 having been several times fused at high temperatures, assumed, 

 on that account, a red-brown colour when first melted. That 

 such sulphur may still appear yellow is evident from the deport- 

 ment of red sulphur (see p. 184). 



In all probability black sulphur is formed at a certain tempe- 

 rature, and the whole sulphur used might be obtained as black, 

 if it were possible to cool every particle suddenly from that tem- 

 perature down to the point of crystallization. As, however, by 

 pouring into water, or in any other manner, all parts are not 

 cooled equally quickly, only a small portion of black sulphur can 

 in general be obtained. 



In order to study the influence of repeated cooling more pre- 

 cisely, a quantity of common sulphur was retained for eight 

 hours at a temperature of 300° C. and then suddenly cooled. It 

 assumed the colour of common sulphur with a slight trace- of 

 green. For the sake of comparison, a similar quantity of the 

 same sulphur was, during these eight hours, heated ten times to 

 300° C, and every time quickly cooled by pouring it on a moist- 

 ened glazed earthenware plate. The one which was fused ten 

 times became more red-brown after each cooling ; and although, 

 on the whole, it had been kept a much shorter time at a high 

 temperature it appeared deep red-brown after the last cooling, 

 and deported itself in the same manner as above described in the 

 case of remelted sulphur ; that is, it was soluble in, and gave a 

 red solution with bisulphide of carbon, and the insoluble part 

 gave black sulphur. On the contrary, the quantity of sulphur 



* In determining these high temperatures, I used the air thermometei 

 which I described in Poggendorff's AnrMlen, vol. Iv. p. 1. 



