( 210 ) 



that of a wire uf' 1 lie same metal with a proportion of admixture x 

 at the same temperature, r x r ■ According to a theorem of Matthiessen ') 

 derived from observations between 0° and 100°, this difference (the 

 theorem refers to a difference that is about the same as that con- 

 sidered here) is constant for different temperatures. Fleming") found 

 this theorem about confirmed down to — 200°. As we have found, 

 this theorem "no longer holds for hydrogen temperatures. But the 

 deviation is not of such a nature as to affect our conclusions. So 

 if to form an idea of the influence of the admixtures, we put 

 ry = i'iT -\- px, further p constant and large, then it is clear that 

 — when r-,T becomes as small as is the case (see Table I Auy) 

 for pure metals and hydrogen temperatures — the resistance of a 

 metal for the case that x gets an appreciable amount, will be owing 

 almost exclusively to the admixture. The small amounts of admixture 

 obtain a remarkable influence '). 



Analogues are easily found in the important influence of small 

 amounts of admixture on the density in the neighbourhood of the 

 critical temperature of a substance, in a space becoming opaque by 

 a cloud depositing on a minimum quantity of dust. But for a further 

 discussion the systematic investigation of the influence of small 

 amounts of admixture should be more advanced. At all events the 

 changes of the resistance with temperature at hydrogen tempera- 

 tures proves to be a highly sensitive criterion to decide about the 

 nature of a metal. 



§ 2. Gold. The different samples of pure gold were all supplied 

 by Dr. C. Hoitsema. Wifh the exception of two the wires were all 

 treated in exactly the same way, drawn out by Heraeus to 0,1 mm. 

 diameter, and treated at every pull with diluted sulphuric acid and 

 nitric acid. The gold wire Auyi was drawn in a different way and 

 made strongly impure. The exact amount has not yet been ascertained. 



i) Pogg. Ann. Bd. GXXII. 



! ) Proc. Royal Institution June 1896 p. 9. 

 • s ) To a less degree of purity of the examined metal wires it is perhaps to be 

 ascribed that Niccolai, Att. Line. 10, 1 st sem. p. 906 finds a smaller decrease of resi- 

 stance at — 189° than we do, as appears by comparison with Tables I, 111, V 

 of this communication and V of Comm. N°. 96&. Indeed Niccolai finds : 



