8 Cornwall — Greenockite on Calcite from Joplin, Mo. 



cubic centimeters of water. Tlie whole was then saturated with 

 hydrogen sulphide gas, giving very quickly a yellow precipitate, 

 and this, after letting the gas act long enough, was filtered off, 

 dissolved in strong hydrochloric acid, evaporated with sulphuric 

 acid, ignited and weighed as sulphate. By this means the 

 coating tested was found to contain 23'07 per cent of cadmium, 

 or 29*66 of cadmium sulphide. It should be said that the 

 coating yields sulphur dioxide when roasted. 



By comparing the liquid holding in suspension this cad- 

 mium sulphide with another in which a known amount of cad- 

 mium sulphide had been precipitated, it had already been 

 estimated that the yellow coating on the calcite contained not 

 less than 15 per cent of cadmium. 



Finally, although the Joplin sphalerite on which greenockite 

 occurs will give a distinct reaction for cadmium when roasted 

 and reduced with charcoal in the closed tube, in the manner 

 already described, yet it was found that no precipitate could 

 be obtained from it by hydrogen sulphide, even after thirty 

 minutes action, the treatment being quantitatively, and in 

 every other respect, exactly the same as described for the 

 yellow coating on the calcite. A mixture corresponding to a 

 sphalerite containing 5 per cent of cadmium yielded a precipi- 

 tate of cadmium sulphide, under identical conditions, in a few 

 minutes. Dana (System of Mineralogy, 6th ed.) states that 

 the amount of cadmium present in any sphalerite thus far ana- 

 lyzed is less than 5 per cent. 



It therefore appears certain that this yellow coating on the 

 calcite, like that on the Joplin sphalerite, is greenockite. 



John C. Green School of Science, 

 Princeton University. 



