HOLMAN, LAWRENCE, BARE. — MELTING POINTS. 225 



in the circuit. Tlie last was found to be negligible throughout the 

 work. 



To observe the melting point, the furnace containing the metal is 

 heated more or less rapidly until the meltiug point is approached. 

 The blast lamp is then adjusted to give a slowly rising temperature. 

 The thermal circuit, with the couple previously fused into the metal, 

 is connected to a suitable section of a, h, c, d. The rheostats are con- 

 tinually adjusted for zero deflections of the galvanometer, G, and the 

 corresponding readings of A are taken. These will show gradually 

 increasing values, but the rise will presently be interrupted by a 

 series of constant readings, after which the readings, will again steadily 

 increase. This period of constant, or nearly constant, readings of A is 

 that in which the latent heat of fusion is being absorbed, and its dura- 

 tion is frequently several minutes. The temperature at that time is, 

 of course, that of the melting point. The reverse process, starting 

 with the metal in a molten state and cooling it gradually, shows a 

 similar period of solidification. 



No difference was discovered between the ascending and descending 

 readings when a sufficient amount of the metal and a slow rate of 

 heating and cooling were employed. With small amounts the steady 

 reading was more or less masked by phenomena which were clearly 

 due to inequality in distribution of temperature throughout the mass 

 of mixed liquid and solid metal. In the case of aluminum, however, 

 something more than this irregularity was observed, as elsewhere 

 stated, but the time at command did not permit a study beyond the 

 point of satisfying ourselves that the point observed was unquestion- 

 ably the true melting point. 



This work was done chiefly as the thesis work of Messrs. Lawrence 

 and Barr. The efficient assistance of Mr. C. L. Norton contributed 

 materially to its progress and success. 



The computation of temperatures t from the observed electro-motive 

 forces 2 6 involves a knowledge of the function connecting the two, 

 i. e. of the function 



ne=f(t) or t = F(lU)' 



This problem has been elsewhere discussed by one of the authors of 

 this paper.* 



In that article two interpolation formulae were developed. They 

 were respectively of the following forms, applying to the case where 



* Holman, These Proceedings, ante, p. 193. 

 VOL. XXXI. (n. s. xxiii.) 15 



