362 Prof. W. Kamsay and N. Eumorfopoulos on the 



1892), and the other by Messrs. Heycock and Neville (J. C. S. 

 Trans. .1895, p. 160). By a somewhat violent extrapolation* 

 from a formula which, as far as we know, has been compared 

 with the air-thermometer only to about 625°, they obtain : — 



Heycock and 

 Callendar. Neville. 



Freezing- or melting-point of silver ... 982° 961° 



,, „ gold 1091° 1062° f 



Callendar then, taking the melting-point of silver as 945°, 

 makes the melting-point of gold 1037°. Now Violle's deter- 

 mination for silver is 954°, which, using Callendar's formula, 

 would give for gold 1049°. Holborn and Wien's value for 

 silver is 968°. In view of the variance between the numbers, 

 it was determined to take Violle's value, though the correct 

 value may be a few degrees higher (compare Le Chatelier, 

 C. JR. cxxi. p. 323, 1895). In any case, allowance can easily 

 be made, when further researches have determined the true 

 melting-point. 



The gold used by us was a very pure specimen obtained 

 from Messrs. Johnson and Matthey. The salts used, with the 

 exception of some of the iodides, were pure specimens, pre- 

 pared specially by ourselves. In a few cases the salts so 

 prepared were recrystallized, and melting-points were taken 

 both of the recrystallized salt and also that obtained from the 

 mother liquor. No difference could be detected, and hence 

 no further mention is made of these determinations. 



Gold on melting alloys with the platinum, and hence must 

 destroy to a certain extent the uniformity of the ribbon. A 



* In Holborn and Wien's last paper {he. cit.) the resistance of pure 

 platinum is determined at different temperatures with their thermo- 

 element, and their results cannot be expressed quite satisfactorily ("nur 

 ungeniigend") by means of Callendar's formula. The resistance of two 

 of their pure platinum wires began to differ beyond about 900°, while 

 agreeing below this temperature. They therefore consider this property 

 unsuited to extrapolation. 



t In a recent paper (J. C. S. Trans. 1895, p. 1025) Heycock and 

 Neville state that " Callendar did not rigidly follow the method of cali- 

 bration, which was afterwards developed by Griffiths and himself, and 

 which we have always adhered to. That method requires that the 

 resistance of the pyrometer should be determined at three standard tem- 

 peratures," viz., at 0°, 100°, and the boiling-point of sulphur, 444 c, 5. 

 And lower down they say, u If Callendar had standardized his thermo- 

 meter on the boiling-point of sulphur . . . . ; " hence they infer that Callen- 

 dar did not use the boiling-point of sulphur for this determination. But 

 the determination of this boiling-point is given in Phil. Trans. 1891, i. e., 

 it was published before the paper referred to, and the latter is also later 

 than another paper (Phil. Mag. July 1891, p. 109), in which the boiling- 

 point of sulphur is directly referred to. We do not quite see how to 

 reconcile the various statements. 



