GEOPHYSICAL LABORATORY. 141 



PUBLICATIONS. 



Brief reviews of the papers published by members of the Laboratory 

 staff during the current year follow. 



(1) The utilization of diffusion processes in the preparation of pure substances. John 



Johnston. J. Am. Chem. Soc, 36, 16-19 (1914). 



Many slightly soluble substances, when formed by precipitation in the 

 ordinary way, are very fine-grained, and consequently contain occluded 

 impurities which are not easy to get rid of; but by taking advantage of the 

 slowness of diffusion in liquids, one can secure very slow precipitation, and in 

 this way prepare such substances in relatively large crystals free from impurity. 

 By this means, for instance, one can readily obtain crystals of calcium hydrox- 

 ide (Ca(0H)2) in the form of hexagonal prisms 3 mm. long with the base 1 mm. 

 thick, or crystals of barium sulphate as much as 2 mm. long. 



(2) A method for determining magnesium in calcium salts. J. C. Hostetter. Jour. Ind. 



Eng. Chem., 6, 392-396 (1914). 



The usual methods for the determination of magnesium in the presence of 

 calcium are not applicable when the latter element amounts to as much as 

 1,000 times that of the magnesium. The essential feature of the method here 

 presented is the concentrating of the magnesium into a precipitate containing 

 but a small amount of calcium. This concentrating is effected by precipitating 

 Mg(0H)2 with a slight excess of solid Ca(0H)2. The magnesium in this pre- 

 cipitate is determined as pyrophosphate after removal of the calcium by two 

 oxalate precipitations. Determinations in some 30 highest-grade calcium salts 

 show, generally, far more magnesium than reported by the makers. 



(3) Calibration tables for copper-constantan and platinum-plantinrhodium thermo-elementa. 



L. H. Adams. J. Am. Chem. Soc, 36, 65-72 (1914). 



Thermo-elements, if they are to yield accurate readings of temperature, 

 must frequently be recalibrated by determination of their electromotive force 

 at a series of fixed points and subsequent interpolation. The labor of inter- 

 polation is minimized by the aid of the tables presented in this paper, which 

 give temperatures and temperature differences for each 100 microvolts up to 

 the limit of usefulness of each thermo-element, and are used in combination 

 with the appropriate derivation curve deduced for each element from the 

 observations at the fixed points. 



(4) The occurrence of molybdenum in rocks, with special reference to those of Hawaii. 



John B. Ferguson. Am. Jour. Sci. (4), 37, 399-402 (1914). 



This article deals with the unexpected discovery of traces of molybdenum in 

 two basaltic lavas from Hawaii and the question of the distribution of this ele- 

 ment in igneous rocks. Its presence in the two basalts reopens the question 

 of its occurrence, since it was thought to be confined entirely to the more 

 siliceous rocks. Tests were accordingly made on a trachyte obsidian from 

 Hawaii, on some sodic, and especially on some nephelite-bearing igneous rocks 

 from other localities. From these it would appear that the presence of molyb- 

 denum is not correlated with high soda or potash content. Except for its 

 well-known tendency to occur in the more siliceous rocks, it therefore seems to 

 be influenced by regional rather than by general chemical characters. 



(5) The optical properties of azurite and alamosite. H. E. Merwin. J. Wash. Acad. Sci., 



4, 253-254 (1914). 



For sodium light, the optical constants of the two minerals are as follows: 

 Azurit6, a = L730, /3 = 1 .758, 7 = 1 .838, 2 7 = 68° ; alamosite, a = 1 .947, iS = 1 .961 , 

 7 = 1.968,27 = 65°. 



