Effect of Temperature, Acidity, etc. 



417- 



2. Zinc concentration. — The experiments which were made 

 on this point were all carried out at 300° and lasted 24 hours. 

 The products from the more concentrated zinc solutions usually 

 contained considerable amorphous material while the crystal- 

 line portion was generally poorly developed. The microscopic 

 analyses are therefore more difficult and presumably less trust- 

 worthy. Nevertheless the study of the analyses of products 



Table VII. 



Influence of zinc concentration on the crystal form of zinc sulphide 

 at 300°. Time 2J+ hours. 











Per cent 



Per cent wurtzite 











wurtzite 



in products from 



Initial 



Final 







in crystal- 



2% ZnS0 4 .7H 2 



H 2 S0 4 



H 2 S0 4 



ZnS0 4 .7H 2 



Percent 



line 



solutions and the 



in wt. % 



inwt. % 



in wt. % 



amorphous 



portion 



same final H s S0 4 . 



2 



2-0 



5 



50 







40 



2 



2-9 



5 



25 



65 



90 



2 



1-6 



5 



5-10 



5 



15 



2 



1-5 



5 



40 



15-20 



10 



2 



2-5 



10 



? 



50 



70 



2 



3-7 



10 



? 



50. 



100 



2 



2-7 



10 



considerable 



50-75 



70 



2 



3-0 



15 



50 



100 



100 



2 



3-1 



15 



25 



100 



100 



2 



5-6 



15 



5-10 







100 



2 



8-0 



20 



25 



100 



100 



2 



6-7 



20 



35 



100 



100 



2 



6-7 



20 



25 



100 



100 



2 



2-9 



20 



90 



50 



100 



precipitated from solutions containing 5 per cent to 20 per cent 

 of hydrous zinc sulphate (Table VII) brings out a number of 

 interesting points. First, an increase in the zinc concentration 

 increases the percentage of wurtzite in the product, as is shown 

 by a comparison of the results in Table YII, with the product 

 obtained from the same initial acid (2 per cent) and a dilute zinc 

 sulphate solution (2 per cent) (Table XI). In the latter, 

 indeed, only sphalerite was obtained. The observer might at 

 first attribute this effect to the influence of the varying zinc 

 concentration. There is a simpler explanation, however. The 

 action of hydrogen sulphide on the zinc salts results in the 

 formation of sulphuric acid as well as zinc sulphide, and, 

 since the sulphide precipitate naturally increases with the zinc 

 concentration, so also does the acidity increase. 



