THE ELECTRIC CONDUCTIVITY OF NITRIC ACID. 



375 



compared with the standards in the possession of the Cavendish Laboratory, 

 Cambridge. We desire to express our appreciation of Mr. GKIFFITHS' courtesy and 

 kindness in this matter. Two sets of determinations were made at different times 

 and at slightly different temperatures. The results are given as true ohms, when the 

 thermometer used always for the box registered a temperature of 16. 



TABLE III. 



With the exception of the 50-ohtn coil the results are concordant to within 

 '001 ohm, and in the majority of cases to '0005 ohm, which is within the limit of 

 experimental error. 



The values of the higher coils were referred to the 50-ohm coil by reducing the 

 bridge arm to y^y ; they are not, therefore, of such a high degree of accuracy, but 

 these coils were seldom required. 



TEMPERATURE COEFFICIENT OF BRIDGE WIRE. 



The bridge wire, supplied by Messrs. JOHXSON and MATTHEY, was of platinum- 

 (90 per cent.) iridium (10 per cent.) alloy ; its mean diameter was 1*5 millim. 



In order to determine its temperature coefficient, a small portion was drawn out to 

 005 millim. diameter, and the wire introduced into a Call endar- Griffiths pyrometer. 

 Its resistance at the three temperatures of steam, ice, and 20' 15 was determined 

 by one of their platinum resistance boxes, in which the compensating leads are 



