IOWA ACADEMY OF SCIENCES. 



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reach an equilibriuiii in this reaction. To this end the fol- 

 lowing series of determinations was made. As may be 

 seen from the table the precipitation is most rapid about 

 an hour after the beginning, then falls slightly and soon 

 becomes nearly uniform. In general it may be said, that 

 within the total period, the amount of precipitation is 

 nearly proportional to the time, and at the end of seven 

 and a half hours the reaction is yet far from a state of 

 equilibrium. The result is plotted in curve "M," and 

 from it one might easily infer that with sufficient time the 

 precipitation of zinc even in this strength of acid might be 

 complete. 



Experiments were now undertaken to ascertain the 

 influence of time alone. The results are given in the 

 table below, in which X represents the time during which 

 the gas was passed through the solution, and Y gives the 

 time during which the solution was allowed to stand in 

 contact with the precipitated zinc sulphide before it was 

 filtered and the zinc determined. The results evidently 

 point to a three-sided equilibrium between hydrogen 

 sulphide, zinc chloride and hydrochloric acid: 



