308 



Mr. G. H. Martyn on the Discharge 



varied by means of a variable resistance in the circuit, and 

 so the temperature of the loop altered as desired. A volt- 

 meter was connected to the ends of the platinum loop, so that 

 from its readings and the current the resistance of the platinum 

 could be determined. 



The resistance of the loop was measured at 15° 0., at the 

 melting-point of pure K 2 S0 4 (1066° C.) and just at its own 

 melting-point (1710° C), and from its resistance its tempe- 

 rature on the platinum temperature-scale could be calculated. 

 The temperatures on the platinum scale were reduced to the 

 ordinary scale by means of the parabolic formula 



pt ~ A \l066 1 )l066 



whe 



re 



1066' 

 t = temperature on centigrade scale, 

 pt = temperature on platinum scale. 

 The constant A was obtained from the observed resistances 

 at 15° C. and 1710° C. 



The platinum loop and the brass cylinder were maintained 

 at a" difference of potential of 200 volts, and the current from 

 the brass cylinder to the wire was measured with a 

 galvanometer. 



The hydrogen was prepared from pure zinc and hydro- 

 chloric acid, and was dried by KOH and passed through 

 the glass tube for a considerable time. 



The calcium oxide was deposited on the platinum by 

 immersing it in a strong solution of calcium nitrate and 

 heating, 



It was found that the leak was considerably increased when 

 the platinum wire was in hydrogen, and also that a coat of 

 lime increases the leak, the two effects being added when the 

 lime-coated wire was heated in hydrogen. 



The following tables give the results obtained. 



V is the P.D. between the ends of the wire. 



A is the current through the wire in amperes. 



T° is the temperature of the platinum. 



C is the corresponding current from the brass cylinder to 

 the platinum wire. 



I. Platinum wire in Air. 



V. 



A. 



T°0. 



C (amperes). 



32 



4-2 



1570 



6xHT 8 



3-35 



4-3 



1621 



15 „ 



3-5 



437 



1690 



30 „ 



1 



