]04 REPORTS OF inve;stigations and projects. 



temperature at 575 ± 2°. Proofs that these represent an energy change 

 were obtained by the perceptible variation in heat capacity in this region by 

 the Frankenheim method of heating and coohng curves, and also by direct 

 determination of the specific and latent heats in this region. 



Crystallographic proof of the change has been studied in detail by O. 

 Miigge, who finds the high temperature phase, /S-quartz, to be in all proba- 

 bility hexagonal and trapezohedral-hemihedral, while the low-temperature 

 a-quartz is hexagonal and trapezohedral-tetartohedral. This particular rela- 

 tion between the two phases entails certain consequences which can be used 

 as criteria to distinguish quartz which has been heated above 575° from 

 quartz which has never reached that temperature. 



These criteria were in large part indicated by O. Miigge and have been 

 applied here to a number of natural quartzes occurring in dififerent kinds of 

 rocks, the net result of the investigation being that vein and geode quartzes 

 and certain large pegmatite quartz-masses and pegmatite veins were formed 

 below 575°, while graphic and granite pegmatites and granites and porphyry 

 quartzes were in all probability formed above 575°. With the quartzes thus 

 examined were associated other minerals, the order of precipitation of which 

 relative to that of the quartz could be determined in certain instances, and 

 thus temperature limits for the formation of these in turn ascertained. 



(8) The relation between the refractive index and the density of some crystallized 



silicates and their glasses. Esper S. Larsen. Am. Journ. Sci. (4), vol. 28, 

 263. 1909. 



An experimental study of the refractive indices and densities of silicate 

 glasses and of artificial minerals to test the formulae of Gladstone and Dale 

 and of Lorentz and Lorenz. Neither the refractive indices nor the specific 

 volumes of the glasses are strictly additive functions, but there may be an 

 increase or a decrease of volume and a corresponding decrease or increase of 

 the refractive index. The specific refractivity computed from either formula 

 is sensibly additive for the glasses and nearly so for the isomorphous series 

 of soda-lime feldspars, but when crystals are compared with glasses of the 

 same composition, or with other crystals, the values of the specific refractiv- 

 ity, computed from either formula, may dififer by as much as 11 per cent. 

 They are usually higher for the glasses. One formula appears to hold as 

 well as the other, but the formula of Gladstone and Dale has the advantage of 

 simplicity. 



(9) The binary systems of alumina with silica, lime, and magnesia. E. S. Shepherd 



and G. A. Rankin. With optical study by Fred. Eugene Wright and E. S. 

 Larsen. Am. Journ. Sci. (4), vol. 28, 293. 1909. 



This paper contains a large body of experimental data and descriptions of 

 a number of methods which have been developed in the course of the study 

 of the three 2-component systems mentioned, which do not admit of brief re- 

 view. The fact that it has proved practicable to make reasonably accurate 

 determinations of mineral relations at a temperature as high as 2100° C. is 

 by no means the least important result of the experimental work. The most 

 important relations found to exist between the above components are these : 



(i) There is but one compound (ALSiOj) of alumina and silica stable in 

 contact with the melt. This is the mineral sillimanite. The two minerals 



