114 



IOWA ACADEMY OF SCIENCES. 



Four other experiments were performed consecutively 

 upon the same solution with the results given below. In 

 experiment (3) the solution after standing twelve hours 

 was shaken for one and one-half hours, and a portion fil- 

 tered off and the zinc determined. It should be mentioned 

 that all the solutions after long standing smelled strongly 

 of hydrogen sulphide. 



Series III and IV are not comparable since the precipi- 

 tation vessels and the volumes of the solutions were not 

 the same. 



Even though the agitation seemed to have little effect 

 as shown in Series IV, it seemed desirable to try a series 

 of experiments to determine the effect of agitation while 

 hydrogen sulphide is passing through the solution. To 

 this end two solutions at the same temperature were sim- 

 ultaneously treated with hydrogen sulphide flowing from 

 two generators and at very nearly the same rate. In one 

 of the tubes was a small stirrer. The effect seems to be a 

 slight acceleration of the reaction. 



The effect of temperature was next considered. A new 

 solution of zinc containing 3.94 per cent of hydrochloric 

 acid and 3.49 per cent of zinc was used, with the results 

 given in Series VI. 



