128 



Dr. J. Erskine-Murray. 



Table II. Permanent Changes produced in Contact-potential of 

 Metals by washing with Alcohol and drying in Air. 



sufficient to retain it if its depth were not more than 0'3 or 0'4 cm. 

 In other cases a shallow metal dish was used. The behaviour of 

 water puzzled me for some time, and made me realize the extreme 

 difficulty of obtaining a clean liquid surface. After some preliminary 

 experiments I found that distilled water which has not been exposed 

 to the atmosphere gives fairly constant results when lying to a depth 

 of 0'2 cm. on one of the standard gold plates. When water on gold 

 formed the one plate and a dry standard gold plate (see 8) the 

 other, the value found was O'lO volt, the water being negative. Thus 

 clean water in contact with gold is about O'lO volt negative to it. 

 The value found is quite different if the water has been exposed to the 

 air for some time, and is usually positive instead of negative to the 

 standard plate. 



46. Air expelled from the lungs produces a very marked change 

 in the contact-potential of water. By blowing through a fine glass 



