126 A. L. Day and E. B. Sosman — 



Zinc. — Two samples of " C. P. sticks " were used, both 

 from Eimer and Amend. No appreciable difference could be 

 observed between their melting points. Both melting and 

 freezing points were sharp and measurable to a fraction of a 

 microvolt. Successive readings did not differ by more than 

 one microvolt. The charge was about 200 grams. The analy- 

 sis has been published.* 



Antimony. — Two samples of metal were used, both from 

 Kahlbaum, and no appreciable difference was found between 

 their melting points. An analysis of the first sample is given 

 in section 6. The charge weighed about 150 grams. The 

 melting point is sharp and does not differ from the freezing 

 point by more than one microvolt, provided the undercooling 

 which always precedes solidification does not exceed 15°. If 

 the metal is undercooled too far to give an accurate freezing 

 point, the fact is easily recognized by observing that the 

 thermoelement does not return to a sustained constant tem- 

 perature, but merely rises to a maximum, then falls again. The 

 amount of undercooling is greater the higher the metal has 

 been heated above its melting point after the melting is com- 

 plete. 



Silver. — The charge weighed about 260 grams. Only one 

 supply was used, a specially purified sample obtained from the 

 Philadelphia Mint, of which an analysis is given in the previ- 

 ous paper.* The melting and freezing points were sharp and 

 agreed within one microvolt. 



Gold. — A new charge of gold was used, weighing 350 

 grams. This was obtained from Dr. Eckfeldt of the Phila- 

 delphia Mint. No analysis was deemed necessary.* 



Copper. — The copper was obtained in the form known as 

 " copper drops cooled in hydrogen " (Eimer and Amend). 

 Only one supply was used. The melting and freezing points 

 were not quite as sharp as was the case with silver, but always 

 agreed within 1 microvolt. The temperature is very suscepti- 

 ble to a trace of oxide, which not only lowers the temperature 

 appreciably but makes it more uncertain, so that if a little 

 oxidation has taken place it is recognizable at once. Waidner 

 and Burgessf found that the best commercial electrolytic cop- 

 per showed an average difference of 0*2° in the melting point 

 from the purified copper drops. Charge, about 210 granib. 



Diopside. — Two samples of diopside were used, one from 

 the preparation of Allen and White;}: and the other made up in 

 1909 by G. A. Pankin. No appreciable difference was found 



* E. T. Allen, in paper of Day and Clement, p. 454. 

 fLoc. cit., p. 469 (Phys. Eev.) ; p. 174 (Bull.). 

 X This Journal (4), xxvii, 1, 1909. 



