i9o6.] SULPHURIC ACID ON DEPOSITION OF METALS. 257 



When four cubic centimeters of acid were present, considerable 

 retardation in the decomposition was observed ; for at the end of 

 the fifteen minute period, there was still some undeposited zinc. The 

 test at the end of eighteen minutes showed that no zinc was present 

 in the solution. The rate of precipitation was as follows : 



In 2.5 minutes, 0.0668 gram of zinc was deposited. 



That the presence of five cubic centimeters of acid greatly re- 

 tards the precipitation was shown when a solution, containing 

 0.21 10 gram of zinc, was electrolyzed. It was thirty minutes before 

 the last traces of metal were thrown out. 



In 2.5 minutes. 0.0668 gram of zinc was deposited. 

 " 5 " 0.1306 " 



"10 " 0.1980 " 



"20 " 0.2077 " 



"30 " 0.21 10 " 



(Figure i, Curve 5.) 



In these experiments the volume of the solution was increased, 

 in each case, by the addition of the acid. Thinking that, perhaps, 

 the increased period of time might be due to the greater volume of 

 solution, it was observed that the retardation was due principally to 

 the acid present. From a solution of fourteen cubic centimeters 

 volume, containing one cubic centimeter of sulphuric acid, all the 

 zinc was deposited in twelve minutes. In the same volume of 

 solution, containing four cubic centimeters of acid, eighteen minutes 

 were necessary for complete precipitation. 



Copper. 



The volume of the copper sulphate solution in these experiments, 

 as well as in the solutions of the sulphates of the succeeding metals, 

 was ten cubic centimeters, including the volume of the acid added. 



The amount of copper present in the solution was 0.2485 gram. 



