g22 MR CONNELL ON SULPHURET OF CADMIUM. 



We have thus, in the 3.71 grains of the mineral under analysis. 



Sulphur, 837 22.66 



Cadmium, 2,868 77.30 



Iron, traces, 



3.705 99.86 



which agrees completely with the theoretical composition of 



1 atom Sulphur, 201.16 22.40 



1 atom Cadmium, 696.76 77.59 



897.92 99.99 



The mineral is thus a protosulphuret of cadmium, and its formula Cd S. 



It is thus evidently, both physically and chemically, a perfectly well charac- 

 terized and distinct species. The mineral which it ranks nearest in the system 

 is zinc-blende, but from this it differs essentially, not only in its chemical 

 nature, but in its external characters, such as specific gravit}^ and form of 

 crystallization. I believe a ready mode of distinguishing it from the transparent 

 yellow blende, which it resembles a good deal, and with which it was long con- 

 founded, is afforded by the streak, that of the latter being white, whilst that of 

 sulphuret of cadmium is orange-red. The property of becoming red by heat, and 

 returning to yellow on cooling, is possessed in a slight degree by yellow zinc- 

 blende ; but the colour which this latter mineral acquires is not carmine, but a 

 sombre rose tint, and never becomes very deep ; and by a repetition of the heat- 

 ing process, when carried to redness, it gradually loses the property altogether, 

 along with its transparency ; whereas the sulphuret of cadmium may be ignited 

 as often as thought proper, without losing the property or its transparency. 

 This quality, to the extent in which zinc-blende possesses it, does not appear to 

 depend in that mineral on the presence of cadmium, for I was unable to detect 

 that metal in a crystallized and transparent yellow zinc-blende from the Hartz, 

 belonging to Mr Rose of this city, which acquired a rose tint by heat ; and it is 

 scarce necessary to say, that the quality is not possessed by the artificial white 

 sulphuret of zinc thrown down by sulphuretted hydrogen. It therefore appears 

 to depend, in zinc-blende, on the arrangement of particles in crystallization ; 

 whilst, in sulphuret of cadmium, it is an inherent quality of the substance, being 

 possessed in perfection by the artificial sulphuret of cadmium, got by sulphuretted 

 hydrogen. 



The reactions before the blowpipe may also serve to distinguish the two 

 minerals. It is difficult to act on sulphuret of cadmium, per se, from its decre- 

 pitating property ; but when this can be accomplished on charcoal, the usual 

 yellowish-red ring, arising from the oxidation of sublimated cadmium, is formed 

 around the fragment. When mixed with soda, and acted on, on charcoal, this 



