1903.] Heat and of Solvents on Thin Films of Metal. 229 



Tests of the electrical conductivity of films of gold and silver, 

 before and after annealing, have been made for me at the National 

 Physical Laboratory, the following is quoted from the report of the 

 Director : 



" The tests were made on three kinds of films, viz. : 



" (A) Silver leaf on glass or mica. 



" (B) Chemically deposited silver on glass. 



" (C) Gold on glass or mica (applied in oil and reduced by heat). 



" The general result of heating these films to temperatures above 

 300 C. was ultimately to increase their resistance from relatively 

 small values (of the order of 0'2 to 50 ohms) up to very high values 

 (thousands of megohms). 



" It was also noticed, in the case of the chemically deposited silver, 

 that the first heating seemed to produce a considerable fall of 

 resistance (e.g., from 14 ohms down to 2 ohms). Part of this change 

 may have been due to the possibility of making better contacts after 

 the heating. 



"The following description of the specimens sent herewith will 

 illustrate this general result. 



"(A) Silver Leaf. 



R 2 



