136 CARNEGIE INSTITUTION OF WASHINGTON. 



(417) On some natural and synthetic melilites. A. F. Buddington. Am. J. Sci., 3, 35-87. 

 1922. 



Over 100 synthetic crystalline mixtures of 2CaO.Mg0.2Si0 2 , 2CaO.Al 2 3 . 

 Si0 2 , and 3RO.R20 3 .3Si0 2 compounds were prepared from appropriate glasses 

 at temperatures above 1000° (the approximate lower limit of experiments); 

 and their homogeneity, the optical characters of those forming homogeneous 

 mixtures and of the dominant phase of some of those forming inhomogeneous 

 mixtures and the temperatures of complete melting were determined. 



The compounds 2CaO.Mg0.2Si0 2 and 2CaO.Al 2 3 .Si0 2 have previously 

 been shown to form a complete series of solid solutions at the solidus and are 

 here shown to agree very closely in their properties with the akermanite- 

 gehlenite series of minerals. 



In certain homogeneous solid solutions with the other compounds at certain 

 temperatures, 3CaO.Al 2 3 .3Si0 2 is shown to have the properties of a negative, 

 uniaxial, moderately birefringent, crystalline compound. 



Mixtures of 2CaO.Mg0.2Si0 2 , 2CaO.Al 2 3 .Si0 2 , and a third constituent 

 consisting of a mixture of 90 per cent 3CaO.Al 2 O 3 .3SiO 2 +10 per cent SNa^O. 

 Al 2 3 .3Si0 2 form a complete series of solid solutions, except for a trace of 

 inhomogeneity in some preparations high in 2CaO.Mg0.2Si0 2 . Mixtures of 

 these compounds yield crystallized products essentially similar in composition 

 and properties to the minerals of the humboldtilite series, varietal members of 

 the melilite group relatively poor in ferric iron. 



The humboldtilites are interpreted as essentially isomorphous mixtures of 

 positive uniaxial akermanite (2CaO.Mg0.2Si0 2 ) and a negative, tetragonal, 

 uniaxial, moderately birefringent form of 3CaO.Al 2 3 .3Si0 2 with minor 

 amounts of gehlenite, a ferrous iron compound, and 3RO.R 2 3 .3Si0 2 com- 

 pounds. The compositions of the humboldtilites lie in a zone which exhibits 

 the lowest temperatures of complete melting for the components involved. 



Mixtures of 3CaO.Fe 2 3 .3Si0 2 , 2CaO.Mg0.2Si0 2 , 3Na 2 O.Al 2 3 .3Si0 2 , 

 2CaO.Al 2 3 .Si0 2 , and 3CaO.Al 2 3 .3Si0 2 , similar in composition to some of 

 the melilites rich in ferric iron, were studied, and the properties of the crystal- 

 line material were found to be quite different from those of natural minerals of 

 similar composition. 



The natural melilites rich in ferric iron probably form at temperatures lower 

 than those of the present experiments, since some of such melilites investi- 

 gated decompose or invert at temperatures at least as low as 850°. 



Three new analyses of humboldtilites and one of ferric-iron-rich melilite, 

 by Dr. H. S. Washington, are given. The ferric-iron-rich melilite differs from 

 any hitherto analyzed. 



This study serves to emphasize the great complexity of this group of 

 minerals and the necessity for further data on their composition and properties 

 and for further experiments in synthesis. The extent to which such known 

 and hypothetical compounds as 3MgO.Al 2 3 .3Si0 2 , 3FeO.Al 2 3 .3Si0 2 , 3K 2 0. 

 Al 2 3 .3Si0 2 , 2CaO.Fe0.2Si0 2 , 2CaO.Fe 2 3 .Si0 2 , etc., may enter into the 

 melilite minerals, and their corresponding effect, are yet to be studied. 



(428) A furnace temperature regulator. Howard S. Roberts. J. Wash. Acad. Sci., 11, 

 401-409. 1921. 



This temperature regulator is a modification of the regulator described by 

 White and Adams (Phys. Rev., 14, 44-48, 1919). The specially made relay 

 in the air apparatus is replaced by stock apparatus which is equally effective and 

 removes the tendency in their apparatus to bring about slow, cyclic variations 

 in the temperature of the furnace. An attachment for the regulator is described, 

 by means of which the temperature of the furnace may be raised or lowered at 

 a nearly linear rate. This is of use in determining melting-points, transition- 

 points, etc. 



