L89L] Properties of Metals in relation to the Periodic Law. 349 



FIG. 2. 



hotographic record of the cooling of pure gold is represented 

 by the thicker of the dotted lines in fig. 3. The mass of gold had in 

 this case an initial temperature of about 1250 C., which fell to 

 1045 C. when the mass began to solidify. The curve is approxi- 

 mately horizontal during solidification, and throughout its entire 

 course appears to be a perfectly normal curve of a cooling mass of 

 metal, no points of exceptional absorption or evolution of heat, such 

 as would occur in iron, being observable. 



A curve obtained in a similar way, and representing the cooling of 

 gold with 0'5 per cent, of lead, is shown by the thin dotted line 

 in the same figure. It is similar to the one representing the cooling 

 of pure gold, but it will be evident that the presence of lead lowers 

 the freezing point of gold by an amount which is found by measure- 



Iment to be about 7'5 C. 

 A very different molecular condition is, however, established by the 

 presence of aluminium. With 0*47 per cent, of this element the 

 true freezing point can be detected, but is nearly obliterated 

 (fig. 3), and the mass does not become truly solid until the point 

 marked a is reached when the temperature has fallen to 900 6 C. 



It is of interest to ascertain how far the lowering of the freezing 

 point of gold is in accordance with the results of Baoult's investiga- 

 tions on the lowering of the freezing point of solutions. His generali- 

 sations have been tested in the case of solutions of metals in metals 

 with low melting points (tin, lead, and bismuth), in an admirable 

 series of experiments by Heycock and Neville.* In order to calculate 

 the lowering of the freezing point of gold produced by one atom of 

 the added element to 100 atoms of the solvent, which has been the 

 usual method of stating such results, it is necessary to know the latent 



* ' Journ. Chem. Soc.,' vol. 55, 1889, p. 666 ; vol. 57, 1890, pp. 376 and 656. 

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