abstracts: chemistry 



91 



of the olivine forsterite, by reaction with the Hquid to give the pyrox- 

 ene cKno-enstatite. 



Summary of invariant points^ 



SOLID PHASE 



Periclase (MgO) 



Periclase (MgO) 



Forsterite (Mg2Si04) 



Forsterite (Mg2Si04) 



Forsterite (Mg2Si04) 



Clino-enstatite (MgSiOs). 

 Clino-enstatite (MgSiOa). 



Cristobalite (Si02) 



Cristobalite (SiOa) 



LIQUID PHASE 



MgO, 100% 



MgO, 14%Mg2SiO,, 86%..., 



MgaSiO^, 100% ■., 



MgSiOa, 97.5%; Si02, 2.5%. 



MgSiOs, 87.5%; SiOo, 12.5%. 

 SiOo, 100% 



TEMPERATURE 



2800° (Kanolt) 

 1850° ± 20° 

 1890° ± 20° 

 1557° ± 2° 



1543° ± 2° 

 1625° (Fenner) 



1 These points are, of course, invariant only when the system is considered as a condensed system. 



N. L. B. 



CHEMISTRY. — Determination of cuprous and cupric sulphide in mix- 

 tures of one another-. Eugen Posnjak. J. Am. Chem. Soc, 36: 

 2475-2479. 1914. 

 The reaction between cuprous sulphide and silver nitrate was con- 

 firmed in accordance with the equation 



CuaS + 4AgN03 = AgoS + 2Ag + 2Cu(N03)2 

 It was found that silver sulphide only, and no metallic silver, is formed 

 by the reaction between cupric sulphide and silver nitrate, the equation 

 for this reaction being 



CuS + 2AgT^03 = Ago + Cu(N03)2 

 Based on the difference between these reactions, a method is given 

 in this paper for the determination of cuprous and cupric sulphide in 

 mixtures of the two. The mixture is treated with silver nitrate and 

 from the product the metallic silver is extracted by means of ferric 

 nitrate. The amount of cuprous sulphide is calculated from the metal- 

 lic silver, while the cupric sulphide is calculated from the difference be- 

 tween the sUver in the silver sulphide and the metallic silver. 



In mixtures containing the constituents in any proportion whatever, 

 the method was shown to be accurate within 1.5 per cent. E. P. 



CHEMISTRY.- — A method for determining magnesium, in calcium salts. 

 J. C. HosTETTEE. Jour. Ind. Eng. Chem., 6: 392-396. 1914. 

 The usual methods for the determination of magnesium in the pres- 

 ence of calcium are not applicable when the latter element amounts to 



