SOME CONTEMPORAKY .IDf.l.XCr.S IX rilVSlCS—l' biS 



.inythin^; whii-li is clone to the substance alters its constitution cnouKli 

 to affect its resistance. (We shall later see that the situation wi'h 

 many of the metals is almost as bad.) Most of the experiments 

 reveal a steady decline of resistance as the temperature is raised, 

 whether the sample usetl be amorphous or crystalline (graphitic) 

 and whatever its history; but Noyes recently traced several very 

 concordant curves for several samples of graphite (all however of 

 the same provenience) showing a minimum of resistance near 8(K)° C 

 Diamonds have exceedingly high resistances, wiiich f.ill wlicn tlicy 

 are heated. 



Passing over four gases and three metals, we come next to silicon; 

 the curve traced by Koenigsberger shows the resistance descending 

 as the temperature is increased, until at a certain critical temperature 

 it leaps sharply upward; from the new high value it descends again 

 as the silicon is further warmed, only to make a second upward jump; 

 from this second maximum it drops steadily away, at least as far as 

 the highest temperature attained in the experiment. This illustrates 

 another perplexing property of some elements; they have several 

 distinct "allotropic" forms, each of them more or less stable over a 

 distinct range of temperature which may or may not overlap with the 

 ranges of the others; each must be regarded, so far as its conducting- 

 jKJwer is concerned, as a distinct element. In some instances the 

 several forms of an element are vividly contrasted in appearance and 

 in general behavior; such is the case with phosphorus, all of the forms 

 of which have high resistances, but little is known about their trends 

 with temperature. In other cases the anomalous changes of temper- 

 ature with resistance are not accompanied by other striking changes; 

 and there is a tendency to explain any deviation from an expected 

 trend — such as, for example, a maximum in a resistance-temperature 

 curve — by saying that the substance is gradually changing from one 

 form into another. 



Sulphur is the extreme case of high resistance. I know of no data 

 for scandium, which is to be regretted, as there is some reason from 

 general atomic theory for supposing that this element stands at a 

 turning-point of the Periodic Table. Titanium, like silicon, has 

 several modifications, in some of which the characteristic rises while 

 in others it descends. Germanium has been studied lately by Bidwell; 

 it is the element mentioned above which displays a minimum of 

 resistance at — 116°C. Arsenic resembles the metals. Selenium in 

 the dark has an extremely high resistance; its character when il- 

 luminated is too much of a subject to be discussed in this place. 

 Zirconium was found, at least by one observer, to displa>' a minimum 



