GEOPHYSICAL LABORATORY. 141 



Many physico-chemical determinations may now be made with just as 

 great accuracy at high pressures as under ordinary conditions. Apparatus 

 suitable for this purpose has now been developed in several laboratories; 

 some of the apparatus Avhich we have used is illustrated and briefly described. 



(2) A table for linear and certain other interpolations on spectrograms. H. E. Merwin. 



Am. J. Sci. (4), 43, 49-56 (1917). 



The usual formulas for interpolating spectrograms make distance a function 

 of wave-length and require the solution of at least a second-degree equation. 

 If, however, distance is made a function of the dispersion of a prism inter- 

 mediate between glass and quartz, then by means of a table and a linear equa- 

 tion distance can be obtained as a function of wave-length. 



(3) Crystallographic and optic properties of mannoketoheptose and of the osazones 



of mannoketoheptose and mannoaldoheptose. F. E. Wright. .J. Biol. Chem., 

 28, 523-526 (1917). 



Measurements of the crystallographic and optic constants of crystals of 

 mannoketoheptose prove that they are monochnic-hemimorphic in character 

 (digonal polar type) ; etch figures produced by immersing the crystals for 10 

 seconds in alcohol are in accord with this type of symmetry. The osazones of 

 mannoketoheptose and of mannoaldoheptose were prepared and yielded, so 

 far as could be detennined, the same crystal substance which appears in yellow 

 needles and radial aggregates of fairly high refractive index and of medium 

 birefringence. Characteristic of this substance are its abnormal interference 

 colors which range from orange-yellow to blue-green and are the result of 

 remarkably strong dispersion of the bisectrices and of strong spectral absorp- 

 tion of the blue end of the spectrum. 



(4) The sodium-potassiiim nepheUtes. N. L. Bowen. Am. J. Sci. (4), 43, 115-132 (1917). 



This paper gives the results of an experimental investigation of the binary 

 system NaAlSi04— KAlSi04. The soda compound occurs in two enantio- 

 tropic forms, nephelite and carnegieite, with an inversion point at 1248". 

 The high-temperature form, carnegieite, melts at 1526°. The potash com- 

 pound shows two forms, kaliophilite, isomorphous with nephelite, and an 

 orthorhombic form with twinning analogous to that in aragonite. The ortho- 

 rhombic form is apparently stable at temperatures above 1540° and melts in 

 the neighborhood of 1800°. 



The potash compound has a eutectic with carnegieite at 1404°. With 

 nephelite it forms an unbroken series of solid solutions. It is concluded there- 

 fore that NaAlSi04 and KAlSi04 are the fundamental molecules of natural 

 nephelites. But, in addition to these, nephelites contain variable amounts 

 of plagioclase in solid solution, the plagioclase varying from albite to anor- 

 thite, the latter accounting for the lime content and the former for the excess 

 silica of the natural mineral. The composition of nephelite should there- 

 fore be expressed in terms of the four molecules NaAlSi04, KAlSi04, 

 NaAlSisOg, and CaAl2Si208. Reference is made to the petrogenetic importance 

 of the occurrence of the last two (plagioclase) molecules in nephelites. 



(5) Some problems of the oxides of iron. Robert B. Sosman. J. Wash. Acad. Sci., 7, 



55-72 (1917). 



The oxides of iron present problems of great importance to chemistry, 

 physics, geology, and biology. Among the chemical problems are: The solu- 

 bility of oxygen in iron, the relations of FeO to ii'on and to Fe304, the internal 

 structure of the solid solution system Fe203-Fe304, the cause of the peculiar 



