1892.] on Metds at High Temperatures. 507 



point of gold. Beneath this little mass of pure gold, A (Fig. 2), a 

 thermo-j unction, B, is protected by a very thin layer of clay from the 

 metal. The oxy hydrogen flame is made to play on the gold, there is 

 a rapid movement of the spot of light over almost 25 feet of the 

 scale, there is a diminution in the 

 rate of rise near the poiut marked Fig. 2. 



1045°, the melting-point of gold, and a 



then, when the metal becomes fluid, 

 the temperature rapidly rises as 

 more heat is given to the little 

 mass. The source of heat is now 

 removed, the temperature falls, there 



is an arrest just at 1045° C, the freezing-point of gold, and 

 then the spot of light resumes its course as the gold cools down 

 to the temperature of the room. The melting-point and freezing- 

 point of palladium, 1500° C, were then shown in the same way. It 

 should be observed, however, that when a small fragment of palladium 

 is fused in the naked flame of the oxyhydrogen blow-pipe, hydrogen 



Fig. 3. 



appears to be absorbed by the metal ; and this absorption of gas 

 lowers the freezing-point materially, and makes it far less steady 

 than when a fresh piece of metal, cut from a large mass, is fused for 

 the first time. 



When the spot of light is allowed to fall on a sensitised plate ir 

 a suitable camera,* the time-temperature curve, of the cooling metal, 

 traced on a moving plate will be of the form shown in Fig. 3. 



It may be useful to show the method by which these autographic curves are 

 obtained : the following diagram, Fig. 4, is therefore added. 



* Proc. Roy. Soc. vol. xlix. 1891, p. 347. 



2 M 2 



