Day and Sosman — Melting Points of Minerals. 345 



The solidifying points and intervals of silicates, unlike those 

 of most metals, are not as accurately determinable as the melt- 

 ing points and intervals, because of the tendency to under- 

 cooling. The extent of the undercooling varies widely, and is 

 affected by numerous incidental conditions. It may amount 

 to only one or two degrees under one set of conditions ; and 

 for the same substance may become so great under other con- 

 ditions that the material is obtained at ordinary temperatures 

 in the form of glass, which will remain amorphous indefinitely. 



3. Principal Temperature Determinations at the Geophysical 

 Laboratory, 1905-1910. 



In Table I the principal fixed temperatures that have 

 been determined during the past five years in this labora- 

 tory are summarized, and restated in terms of the revised 

 temperature scale. These are not neta determinations. The 

 original thermoelement or optical data have simply been inter- 

 preted in terms of the Day and Sosman scale of 1910. 



All of the early thermoelectric measurements of this labora- 

 tory were interpreted by calculating a curve of the form : 

 e=a + bt + ct 2 from the melting points of zinc, silver, and 

 copper, and using this curve for extrapolation, as has been the 

 general custom since the publication of the work of Holborn 

 and Day in 1899. Occasionally a function of the form 

 t = a + he + ce 2 has also been employed. 



The curve e =f(t) gives temperature values that are about 

 16° low at 1500°, and the curve t = f{e) gives values that are 

 about 33° low at 1500°. At 1100° the correction is only 1-5°, 

 so that temperatures up to 1100° remain practically unchanged. 



The data of Shepherd and Rankin on Binary Systems of 

 Alumina with Silica, Lime, and Magnesia, have already been 

 revised and published in the German translation of that article.* 

 The revision of the other data is here published for the first 

 time. 



The melting points which form the basis of reproduction of 

 the present scale are as follows : f 



Zinc 418-2 



Antimony 6292 



Silver 960-0 



Gold 1062-4 



Copper 1082-6 



Diopside ... .. 1391- 



Palladium 1549- 



Anorthite . 1550- 



Platinum 1755- 



* Zts. anorg. Chem., lxviii, 370-420, 1910. 

 f Day and Sosman, loc. cit., p. 161. 



