A. L. Day and J. K. Clement — Gas Thermometer. 437 



much larger one, on account of the unexpected values obtained. 

 The expansion of pure platinum as determined by Holborn 

 and Day* is given by the equation, 



\= (8868 t + 1-329 f) 10" 9 



while that of platinum, containing 20 per cent iridium, made 

 in the same furnace at the same time, gave 



A.= (8198 t + 1-418 f) 10-°. 



We had expected, as Holborn and Day assumed in their cal- 

 culations in 1900, that the expansion of the 10 per cent alloy 

 ought to fall approximately between the two. When it there- 

 fore became apparent that our observations were leading to a 

 value for the 10 per cent alloy which was of the same order 

 of magnitude as that hitherto found for pure platinum, we 

 were for a long time quite unwilling to accept the result. 

 After the close scrutiny of the apparatus and its limitations 

 described above, all of which, either singly or in combination, 

 appeared totally inadequate to account for the unexpected 

 expansion coefficient obtained, there remained the single pos- 

 sibility that some confusion had arisen in the preparation of 

 the bar ; but Doctor Herseus, who made the bar, would not 

 admit this possibility. Even then, it was deemed wise to 

 make a chemical analysis of the bar itself, and this was done 

 by E. T. Allen of this laboratory, with the result that the 

 iridium content was found to be 10*6 per cent. There appears 

 therefore no further alternative but to accept the irregular 

 variation of the expansion with the percentage composition as 

 characteristic of platin-iridium, following the well-known 

 example of the iron-nickel alloys. 

 The observations follow : 



In Furnace I. 

 Temperature Distribution along the Bar. 



Left 



Middle 



(Corrected 



Eight 















12 cm 



10 cm 



5 cm 



Temperature) 



5 cm 



10 cm 



l 2 cm 



+ 10° 



+ 11° 



+ 7° 



287-7° 



- 4° 



-13° 



-15° 



+ 12 



+ 13 



+ 7 



511-2 



— 2 



— 15 



— 24 



+ 10 



+ 23 



+ 13 



700- 



— 5 



— 21 



— 30 



+ 28 



+ 33 



+ 17 



1044-1 



— 11 



— 31 



-46 



* On the Expansion of Certain Metals at High Temperature, this Journal 

 (4), xi, p. 374, 1901. 



Am. Jour. Sci. — Fourth Series, Vol. XXVI, No. 155. — November, 1908 



ol 



