304 ILLINOIS STATE ACADEMY OF SCIENCE 



ally from a bath of forty parts of saturated copper sul- 

 fate solution, one part of concentrated sulfuric acid, 

 ten parts of distilled water and a few drops of a thin so- 

 lution of gelatine in water. After the copper plate is de- 

 posited the copper wire is cut off close to the tube, and 

 a new piece attached at the constriction with a small drop 

 of solder. After thoroughly cleaning the central por- 

 tion of the tube, the carbon soot is deposited from the 

 flame of burning camphor. The resistance after under- 

 going the treatment prescribed below is mounted inside 

 of a larger protective tube. A small wooden terminal 

 block is clamped to each end of this larger tube, and the 

 terminal wires soldered to a binding post on each block. 

 The results of Longden's investigation of carbon film 

 resistances showed, and the data obtained in the present 

 work confirms the fact that the resistance of such a car- 

 bon film increases with age, very rapidly at first and later 

 more slowly. Fig. 2 shows a curve in which the resist- 

 ance of such a film is plotted on the ordinate against its 

 age on the abscissa. The irregularity of the points plot- 

 ted is due to the diff erence in temperature conditions un- 

 der which the measurements were made. If this curve 

 were continued over a period of several hundred days, it 

 would become almost but not quite parallel to the time 

 axis, indicating that the resistance had become almost 

 constant. It has been the purpose of the present in- 

 vestigation to try by processes of artificial aging (arti- 

 ficial aging referring to any process which produces a 

 definite change of resistance) to hasten the natural 

 changes in resistance, in order that a film might be made 

 to assume a practically constant magnitude in a short 

 interval of time. To do this it has been necessary to 

 study the effects of different aging processes. The re- 

 sults obtained in this study are listed below. Since these 

 results have been obtained from work on not a very 

 great number of films, they can not be stated as positive 

 scientific facts, but they do suggest the probable effects 

 of the different treatments applied. Furthermore, the 

 results can be interpreted on a qualitative basis only, 

 since there are a number of indeterminable factors in- 

 volved in the procedure, such as the exact amount of 



