P. Eskola — Silicates of Strontium and Barium. 333 



Methods of Working. 



The mixtures were made up of pure quartz, specially 

 prepared calcium carbonate, barium carbonate " Squibb \s 

 reagent" and strontium carbonate from "Baker's 

 analyzed chemicals." These substances were dried at 

 150 : C before weighing, and mixed together, melted if 

 possible, chilled and crushed, then reheated and ground 

 twice more. 



The equilibrium relations were ascertained almost 

 exclusively by the quenching method. Heating curves 

 were run in some cases for the purpose of checking the 

 temperature measurements. 



The temperatures were determined by potentiometer 

 and a Pt-PtRh thermoelement calibrated against the 

 melting points of diopside and anorthite. The tempera- 

 tures, for the most part, are not far from the diopside- 

 point, so that the calibration against diopside, together 

 with the temperature limits taken in the quenchings, show 

 the actual degree of accuracy of the work. Therefore 

 those calibrations are stated below. 



Diopside, melting point 1391.5°, in the standard scale 

 corresponds to 14230 microvolts. 



Date (1921) Crystals Melt Correction The systems under 



ix v fi v investigation 



6 April 11100 11150 -4- 105 ") q n ~ n 



28 April 11110 11130 + 105 ) foru-biU 2 



11 Mar 14120 11130 -f 105 BaO-SiO, and SrSiO s -CaSi0 3 



17 June 11090 11110 -f 130 ] 



26 Junea 11310 11330 — 90 



30 June 11310 11330 — 90 ]■ BaSiO-CaSiO, 



5 August 11290 11310 — 70 1 



22 August 11270 14290 . — 50 J 



a Xew thermoelement. 



Iii the determination of the refractive indices I had the 

 advantage of using the improved immersion method as 

 worked out by Merwin. 6 This method involves an 

 improvement in accuracy as well as in completeness, 

 making it possible to determine at the same time disper- 

 sion as well as refractive indices. One determines 

 directly, using a monochromatic illuminator, the wave- 

 lengths for which the refractive indices to be measured 



8 E. Posnjak and H. E. Merwin, The ternary system Fe.O-SO-H.O, J. Am. 

 Chem. Soc, 44, 1965, 1922. 



