172 DR CARGILL G. KNOTT ON THE 



being added in small successive doses. Not till the maximum saturation was 

 reached was the wire subjected to any excessive heating, such as is generally 

 supposed to be necessary to drive the hydrogen out. The temperature was 

 regulated by means of an oil-bath, into which the wire, firmly bound to 

 the ends of stout copper rods, dipped along with the thermometer which 

 measured the temperature. The heating was applied gently by means of a 

 spirit-lamp. 



In the first series of experiments the temperature was raised gradually to 

 about 300° C. ; and in these experiments the loss of hydrogen was beautifully 

 shown in the manner by which the resistance began to decrease at a temperature 

 of about 260° C. A detailed description of two of the dozen experiments made 

 will suffice, as all have almost exactly the same characteristics. I quote ver- 

 batim from my experimental book, just as the entries were made after the 

 completion of the experiment. 



Experiment made on January 27, 1886. 



Resistance of hydrogenium at 10°*2 C. = 93*6 (10~ 2 ohm) 

 (the numbers observed are omitted). 



Description of Results. — Up to temperature 175° C, the resistance of hydro- 

 genium grows at a steady constant rate = - 203 per degree centigrade; or to that 

 temperature 



E=91 ; 4+-203i 



for this particular specimen ; or, more generally, the resistance of a specimen 

 of hydrogenium, whose resistance is 1 ohm at 0° C, is given by the formula 



r = l + -00222£. 



The rate of increase then begins to increase slowly till 220° C. is reached. 



From 220° to 260° the resistance remains practically steady, varying 

 through a range of 1 in 140 — that is, 07 per cent. 



From 260° to 280° the resistance falls off very rapidly, attaining its maximum 

 rate of decrease at 274°. The rate is then -96 approximately. 



At 280° the rate of decrease markedly diminishes, and seems to tend to 

 evanescence till the highest temperature (295°) is reached. 



From this temperature down again to the ordinary atmospheric temperature 

 the resistance diminishes at a steady and almost constant rate, namely, 202 per 

 degree centigrade ; or 



E= 63-56 + -202 1 

 or, reduced as above, 



r=l+-00318*. 



