356 



Allen and Crenshaw — Sulphides of Zinc, 



Table VI. 

 The actios of hydrogen sulphide on - 2NZnSO 4 , with varying concentration 



of H..SO4. 



No. 



B a S0 4 



Normality 



Per cent 

 0-49 



o-i 



(V2 



0-98 



0-5 



2-45 



1-0 



4-90 



15 



7-36 



1-5 



7-36 



Approx. time 



before 



ppt. began 



1 niin. 

 5 min. 

 25 min. 

 a few hours 

 no ppt. after 



2 days 

 3 days 



Zn in solution after 

 10 days 



Normality Per cent 



o-oooo 



0-0031 

 0-0089 

 0-0338 



0-0923 



0-000 

 0-010 

 0-029 

 0-111 



0-302 



H 2 SO., after ppt. 



Normality Per cent 



0-300 

 0-398 

 0-691 

 1-183 



1-609 



1-47 

 1-95 

 3-39 

 5-80 



7-89 



* Concentration of ZnSO, in No. 6 was increased to 214 N after 2 days. 



tube* in each case contained 10-15" of 10 per cent ZnS0 4 .7H a O. 

 The time in all cases was 2 to 3 days. The concentration 

 of the sulphuric acid in the latter solutions and the temperature 

 to which the tubes were heated varied in the different experi- 

 ments. 



Exp. 1. Temperature 300°-10^H 2 SO 4 used. The product 

 consisted of spherulitic aggregates, all doubly refracting and 

 having the refractive index of wurtzite. 



Exp. 2. Temperature 300° — 7 - 5^ H 2 S0 4 . Crusts and spher- 

 ules consisting of felted fibers which were unquestionably 

 wurtzite sometimes surrounded by amorphous sulphide, indi- 

 cating that the precipitate first formed was amorphous. 5-10 

 per cent of more transparent irregular masses of isotropic sub- 

 stance having the refractive index of sphalerite. 



Exp. 3. Temperature 300°- 5% H 2 S0 4 . The product con- 

 sisted of globules witli crystal faces growing out of them. 

 Nearly all were isotropic and showed the refractive index of 

 sphalerite, though there was perhaj)s 5 per cent of doubly 

 refracting wurtzite. 



Exp. 4. Temperature 300°-4:^H 2 SO 4 . About 30 per cent 

 amorphous sulphide, the rest wurtzite. 



Exp. 5. Temperature 300° — 1% H 2 S0 4 . The product 

 showed crystalline faces and was apparently isotropic. Prac- 

 tically all of it had the index of sphalerite, though there were 

 a few pieces of amorphous material. 



Exp. 6. Temperature 250° — 5^H 2 S0 4 . The product con- 

 sisted almost entirely of large spherules showing both radial 

 * A platinum tube was used. 



