522 abstracts: chemistry 



which have been widely quoted. A recalculation of his data on the 

 basis of redetermination of his fundamental volume show them to be in 

 good agreement with the new measurements. The bearing of these 

 data upon the occurrence of "floated" slabs of rock in the Palisade 

 diabase is discussed. * A. L. D. 



CHEMIS'SRY.^— A method for the determination of magnesium in cal- 

 cium salts. J. C. HosTETTER. J. Am. Chem. Soc. 1913. 

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

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

 as much as 1000 times that of the magnesium. The essential feature of 

 the method here presented is the concentration of the magnesium into 

 a precipitate containing but a small amount of calcium. This concen- 

 tration is effected by precipitating Mg (0H)2 with a slight excess of 

 solid Ca (0H)2. The magnesium in this precipitate is determined as 

 pyrophosphate after removal of the calcium by two oxalate precipita- 

 tions. Determinations in some 30 highest-grade calcium salts show, 

 generally, far more magnesium than reported by the makers. 



J. C. H. 



PHYSICAL CHEMISTRY.— T'/ie phenomena of equilibrium between 

 silica and the alkali carbonates. Paul Niggli. J. Am. Chem. Soc, 

 35:1692-1727. 1913. 

 This is a record of an experimental investigation of the equilibrium 

 between silica and melted alkali carbonate, at temperatures of 900- 

 1000° and under a pressure of 1 atm. carbon dioxide. A series of ex- 

 periments were made with the carbonates of potassium and sodium, and 

 a few with lithium carbonate. The systems R20-Si02-C02 (R = K, 

 Na, Li), under the above-mentioned conditions behave similarly on the 

 whole, and differ only in details. Silica added to alkali carbonate is 

 transformed into silicate as long as any carbonate remains. In the 

 melts there is equilibrium between carbonate and pairs of silicates, as 

 follows : 



I K2CO3 + KaSisOs ^ 2K2Si03 + CO2 

 II NazCOs + Na2Si03 ^ Na4Si04 + CO2 

 III (presumably) 2Li2C03 + Li4Si04 <^ LigSiOg + 2CO2 

 The solid phases, which separate from the melts, consist of silicate 

 or carbonate, but contain no free silica until the proportion of silica 

 exceeds that corresponding to the higher silicate. The amount of car- 

 bonate depends only on the ratio R20/Si02, when external conditions 

 arc constant ; when this ratio becomes identical with that of the silicate 



