GEOPHYSICAL LABORATORY. 141 



gether misleading; moreover, one may as well guess the final result as arbi- 

 trarily choose the data required in calculating it. From this we see that the 

 application of the above simple principles which determine rock meta- 

 morphism to the complicated rock systems will be no simple matter, but 

 will require extended experimental investigation and a long time. In such 

 investigation the first thing necessary is a definite conception of the general 

 processes of rock metamorphism ; this it was the purpose of the authors to 

 present. The choice of particular problems in this large field will doubtless 

 be aided greatly by a study of natural mineral associations from the physico- 

 chemical standpoint, a study which at the same time will certainly provide 

 us with information bearing directly on the problems at issue. 



(25) Eiiiige physilvalisch-chemische Prinzipien der Gesteinsmetamorphose. John 



Johnston and Paul NiggU. Neues Jalirb. Min. (In press.) 



A German translation of "The general principles underlying metamorphic 

 processes" (Jour. Geol., 21, 481-516, 588-624, 1913). Reviewed under 

 No. 24 above. 



(26) The physical chemistry of Seger cones. Robert B. Sosman. Trans. Am. Ceramic 



Soc, 15, 482-498. 1913. 



The relation of certain simple principles of physical chemistry to the 

 behavior of the Seger pyrometric cones, which are widely used in the ceramic 

 industry for the indication of heat effects in the kilns, is illustrated by 

 experiments and charts. The high-temperature cones Nos. 28 to 42 form 

 a simple two-component series composed of alumina and silica. Their 

 behavior agrees well with the known properties of this system, taking into 

 account the three retarding influences: (1) lack of initial homogeneity, 

 (2) slow rate of fusion of silica, and (3) high viscosity of the melt. Cones 5 

 to 27 are made up of four oxides. It is possible to discuss them, however, 

 as a three-component system of orthoclase, calcium silicate, and aluminum 

 silicate, with excess silica as a relatively inactive addition. In this system, 

 as in the foregoing, the control exercised by the low-melting eutectics upon 

 the indications of the cones is well brought out. 



(27) The phenomena of equiUbria between silica and the alkali carbonates. Paul 



NiggU. J. Am. Chem. Soc, 35, 1693-1727. 1913. 



This is a record of an experimental investigation of the equilibrium 

 between silica and melted alkali carbonate, at temperatures of 900° to 1000° 

 and under a pressure of 1 atm. carbon dioxide. A series of experiments 

 was 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. K2C03+K2Si206;=12K2Si03+CO, 



II. Na2C03-l-Na2Si03 7=lNa4Si04+C02 



III. (presumably) 2Li2C03+Li4Si04Z=lLi8Si()6+2COo 



The solid phases which separate from the melts consist of silicate or car- 

 bonate, but contain no free silica until the proportion of silica exceeds that 

 corresponding to the higher silicate. The amount of carbonate depends 

 only on the ratio R20/Si02, when external conditions are constant; when 



