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metallic cadmium, which had been rolled out to a very thin 
and long strip, with the same sulphurous acid, the reaction 
took place in a similar way to that with zinc. The fluid 
turned first yellow, but still remained clear, which required, 
however, a much longer time than with zinc, then darkened, 
separated a little white sulphur, and precipitated finally a 
large amount of sulphide of cadmium. This is insoluble in 
weak sulphurous acid, and therefore precipitated, while sul- 
phide of zinc, being soluble, is consequently prevented from 
forming. We havea clear case here of separating sulphur 
combining directly with a metal. But this separating 
sulphur seems to have even the power of depriving salts like 
sulphide or hyposulphite of cadmium of its metal, forming 
thereby sulphide of cadmium and sulphuric acid. For 
while in the liquid resulting from the action of sulphurous 
acid upon cadmium, and which has been in contact with the 
metal for only three or four hours, no sulphuric acid can be 
detected before boiling, its quantity will be perceptible 
after standing in contact three or four days, and will increase 
by standing several weeks. This sulphuric acid derives its 
origin from the oxidation of the sulphurous acid by the 
oxigen of the metallic oxide, which is decomposed by the 
separating sulphur. The experiment can be easily made by 
adding a solution of either nitrate or sulphate of cadmium to 
hyposulphite of soda. Upon boiling, a slight opalescence 
only will be observed, as cadmium salts are generally acid, 
but no precipitate of either sulphur or sulphide of cadmium. 
Upon adding, however, a little hydrochloric acid, a heavy 
precipitate of sulphide of cadmium will be obtained im- 
mediately. The sulphur, therefore, from the decomposition 
of the hyposulphurous acid, was decidedly active. 
The original fluid treated in the same way, viz., boiling 
with a little hydrochloric acid, immediately gave a precipitate 
of sulphide of cadmium. Before, however, any marked 
percipitate of CdS was observed, and after the fluid had 
remained in contact with the cadmium for about four hours, 
no sulphuric acid was found to be present, as has been 
already mentioned. Upon acidulating and boiling this 
