56 Sheparcl — New Solution for the Copper Voltameter. 



It is also proper to observe that although the current density 

 was widely varied there is no loss of accuracy, as is shown by the 

 probable errors of a single observation in the different series. 



For current densities of *05 _ or greater the solution was 



cm 5 & 



found to heat a little during the first experiment. Results 

 which were obtained during the rise in temperature of the 

 solution were always slightly greater than those obtained after 

 the solution had become warm and at a uniform temperature 

 throughout. The unequal temperature of the solution may be 

 avoided by stirring or by making a preliminary experiment to 

 warm up the solution. The best way was found to heat the 

 solution by means of a flame to a temperature of about 35 or 

 40° C. before making an experiment. The deposits were then 

 found to be very satisfactory even up to a current density of 



over *07 — ^ and the resulting values of the equivalent to 



agree closely with those obtained with the low current densities. 



The results given in series III, IY, Y and YI were obtained 

 with the solution at a temperature from 35° to 40° C, while 

 series I and II were obtained with the solution at the tempera- 

 ture of the room, about 20° C. We see therefore that the 

 temperature from 20° to 40° C. has practically no influence 

 upon the results given by the solution; but that any inequal- 

 ity in the temperature of the solution will cause slight errors 

 and therefore should be carefully avoided. 



The same solution was used throughout the second part of 

 this investigation. Perhaps fresh solutions would have given 

 more consistent results, but certainly no large error is intro- 

 duced by the repeated use of the solution. 



We may collect the results with this solution as follows : 



The weight of copper deposited is practically independent 

 of the temperature between 20° and 40° C. 



The results are independent of the current density within 

 the limits given. 



The solution may be used a large number of times. 



The solution may be used with a current density two or 

 three times as great as that permissible with others commonly 

 in use, so that to measure a given current a considerably 

 smaller voltameter may be employed than with the older 

 solutions. 



Current-measuring instruments may be calibrated by its 

 means with an error of only about one-tenth of one per cent. 



Sheffield Scientific School, New Haven, Conn. 



