228 Mr. A. T. Waterman on the Positive 



The graph was a perfect straight line as nearly as could 

 be seen. Knowing the resistance at room temperature of 

 the strip actually used in the experiment, the same fiducial 

 points could be calculated for it and a similar temperature- 

 resistance curve obtained. From these the temperature of 

 the strip could be inferred from its resistance with a fair 

 degree of approximation. The actual resistance of the strips 

 used when cold varied from *3 to *8 ohm. 



The method of measurement was chiefly the " balance.'^ 

 method as defined by Richardson *, but readings by [the 

 " slit " method were taken whenever feasible. 



The pressure in the tube in which the strip and connexions 

 were enclosed was always less than 10~ 4 mm. of mercury. 



In the tables that follow, m/H is the ratio of the mass of 

 the ion to that of an H-ion in electrolysis on the supposition 

 that it carries an equal charge. The charge of an H-ion 

 was taken to be 9649 electromagnetic units. B and S refer 

 to the " balance" and "slit" methods of measurement 

 respectively. 



1. Silver Chloride. 



(a) The first specimen used was probably fairly pure, but 

 it was considerably darkened by exposure. A very small 

 amount was moistened with distilled water and placed on 

 the strip, mounted by method (a). The emission from the 

 strip had been driven out for all temperatures below 1000° G. 

 Above this point considerable emission from the Pt would 

 certainly be present. 



The melting point of AgCl is given as 450° C. Permanent 

 emission was first detected at about 400°, but was at that 

 point too small to admit of measurement. 



Mean values. 

 V. H. Method. Temperature. ejm. m/H. 



460° 

 160 1487 B & S to 254-4 37-9 



1100° 



The values for ejm were quite consistent — within about 

 3 per cent, variation from mean — and some forty readings 

 were taken. 



(b) Another specimen of the same salt was placed on 

 the strip under the same conditions, giving the following 

 results : — 



V. H. M. T. e/m. m/H. 



465° 

 140 2030 B & S to 259-8 37*1 



940° 



* Phil. Mag., Sept. 1913, p. 453. 



