52 MERWIN : DETERMINING DENSITY OF SOLIDS 



ture of sodium metasilicate which crystallizes much more slowly 

 than the corresponding lithium salt and often shows undercooling 

 amounting to 150° C. This may be seen from the following data: 



Solidifying temperature of sodium metasilicate 

 1007° (Kultascheff) 1018° (Wallace) 1055° (Gaertler) 1056° (Van Klooster) 



A determination of the melting point of an analyzed specimen 

 of a rather pure sodium metasilicate (Si0 2 49.3 per cent, Na 2 

 50.6 per cent) made under the same conditions which obtained 

 in the preceding experiments, gave the following values with three 

 different rates of heating: 1086°, 1088° and 1088°. The true 

 temperature of change of state is therefore very nearly 1088° C. 

 (10,600 microvolts in terms of element G, Day and Sosman). 



Cooling this particular charge for an observation of the solidi- 

 fying temperature gave, upon the first trial, 1046°, following 

 undercooling to 1017°; upon the second trial, 1050°. In the third 

 trial, a particle of solid substance was introduced which precip- 

 itated crystallization suddenly at 1057°. The solidifying tem- 

 perature was therefore much below the melting temperature, even 

 under the most favorable conditions of work. It appears to fol- 

 low from this that the solidifying temperatures of sodium meta- 

 silicate given in the literature have little or no significance as 

 determinations of real equilibria. The true melting point is 

 1088° C. 



The refractive indices of the sodium salt are about 1.527 and 

 1.518 and the birefringence about 0.01. 



PHYSICS. — A method for determining the density of certain solids 

 by means of Rohrbach , s solution having a standard refractive 

 index. H. E. Merwin, Geophysical Laboratory. Com- 

 municated by A. L. Day. To appear in the American 

 Journal of Science. 



By means of Rohrbach's solution so prepared that the relation 

 of its density to its refractive index is known, the density of suit- 

 able solids between 2 and 3.5 can be determined rapidly and accu- 

 rately on the total refractometer by finding the refractive index 

 of the solution while fragments of the solid are suspended in it. 



