126 



TRANSMISSIVITY IN PASSIVE IRON WIRES 



Fig. 3 represents graphically the relation between the complete 

 recovery time and the concentration of acid, as observed in the two 

 sets of experiments just described. The curve approximates a 

 straight line, indicating that the time is nearly proportional to the 

 excess of concentration above a critical value (of about 53 to 54 per 

 cent). 



Influence of Temperature on Recovery Process. 



Eight series of determinations in 65 per cent acid were made in the 

 manner described at the temperature of about 3°, the dish containing 

 the acid being kept cool during the experiment by immersion in snow. 

 The results are given in Table VI. 



TABLE VI. 



Concentration of HNO3, 65 Volumes Per Cent. Temperature 3°. 



It will be observed that recovery is four or five times slower at 3° 

 than at 20°, only three cases out of eight showing full transmission 

 after 16 minutes of recovery. There are also several other differences 

 in the behavior of the wires at the two temperatures. The speed of 

 transmission is several times slower at the low temperature; this re- 

 tardation is perfectly distinct to the eye, but as yet no exact measure- 

 ments of velocity have been made. The local reaction shows a less 



