110 IOWA ACADEMY OF SCIENCES. 



CONTRIBUTION TO THE STUDY OF REVERSIBLE 

 REACTIONS. 



W. N. STULL. 



The object of this investigation has been to determine 

 the points of equilibrium in the reactions resulting when 

 solutions of metals are treated with hydrogen sulphide, 

 and to determine the changes of those points with regard 

 to changes of temperature. As the work advanced the 

 importance of the question of the rate of the reactions 

 became more and more apparent, and as a result I have 

 dealt at considerable length with this factor and with the 

 effects of temperature and agitation upon it. 



The two metals first employed are zinc and cadmium, 

 chiefly because an investigation of the action of hydrogen 

 sulphide upon these would not only serve the original pur- 

 pose of the study, but, it was thought, might throw consid- 

 erable light upon their quantitative separation. The present 

 paper, which is to be considered as merely preliminary, 

 deals with the rate of the reactions in solutions of zinc 

 and cadmium. 



Of course when hydrogen sulphide acts upon zinc chlo- 

 ride we have a reversible reaction represented as follows: 



ZnCl. i H,S :irr^ 2HC1 + ZnS, 

 which in the beginning runs rapidly from left to right, but 

 diminishing as zinc sulphide and free hydrochloric acid are 

 formed and react upon each other in the direction from 

 right to left. By "diminishing" is here meant the dimin- 

 ishing effect, and not the rate of interaction between the 

 molecules. This is dependent only upon the concentra- 

 tion of the reacting substances, and a specific rate of the 

 reaction which is independent of the concentration. 



