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 2 + H 2 S 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. 
