Cadmium, and Mercury. 



355 



More work on this subject is under consideration, but the 

 results given show well enough that hydrogen sulphide will 

 in time precipitate zinc from solutions which are quite strongly- 

 acid. 



Fig. 4. 



o 































































































































































0-3 





































































/ 







































/ 





































/ 



/ 





































/ 









0-2 































/ 



















































































































































/ 













n-1 

























/ 













































































































































































































12 3 4 5 6 7 8 



Percentage of sulphuric acid. 

 Fig. 4. Influence of free acid on the precipitation of zinc sulphide. 



Crystalline zinc sulphide from acid solutions. 



A great number of experiments have been made with the 

 purpose of preparing crystalline zinc sulphide from acid solu- 

 tions at low temperatures, yet so far without success. This 

 seems very remarkable when we consider how slowly the sul- 

 phide forms in strong acid solutions (see Table VI), and we 

 have as yet no explanation for it. At temperatures of 250° 

 and upward, by the use of the double-tube method* crystalline 

 products can be obtained. The results are sufficiently interest- 

 ing to be stated in detail. In all the experiments the source 

 of hydrogen sulphide was about 6 g. Na s S a O, . 5H„0 in 15- 

 20 cc water, which was placed in the outside" tube. The inside 

 * Allen, Crenshaw and Johnston, this Journal, xxxiii, 174, 1912. 



