132 CARNEGIE INSTITUTION OF WASHINGTON. 



The unusual number of papers published during the current year by 

 members of the Laboratory staff, which will be reviewed individually in the 

 following pages, precludes further discussion of their more general aspects 

 in this place. 



PUBLICATIONS. 



(466) Summary of the literature relative to the formation of film on polished glass surfaces. 



George W. Morey. J. Opt. Soc. Amer., 6, 688-693. 1922. 



The stability of polished glass surfaces is of prime importance in the design 

 and manufacture of optical instruments, and all factors aJEf ecting their stability 

 are worthy of careful consideration. Some glasses are inherently inferior in 

 their resistance to the corrosive action of water and weak acids; other glasses, 

 possessing a high degree of resistance to such "weathering" action, often give 

 trouble by becoming covered with a coating resembling that produced by the 

 weathering of an inferior glass, but actually due to entirely different causes. 

 This particular type of coating has been called "film," and this report sum- 

 marizes the information contained in the literature on the formation, appear- 

 ance, cause, and prevention of film on polished glass surfaces. 



(467) The silicates of strontium and barium. Pentti Eskola. Am. J. Sci., 4, 331-375. 



1922. 



This paper contains investigations of the binary systems SrO-Si02, 

 BaO-SiOz, SrO.SiO2-CaO.SiO2, and BaO.SiO2-CaO.SiO2, and of certain more 

 complicated strontium and barium silicates. For the system SrO-SiOz 

 there occur the following compounds: SrO, 2SrO.Si02 SrO.Si02, and Si02. 

 The strontium metasilicate, SrO.Si02, was obtained as crystals which are 

 clearly hemimorphic, apparently hexagonal, but really probably monoclinic. 

 Optically they are closely similar to those of CaO.Si02 with which they form a 

 continuous series of mix crystals with a minimum in the melting curve. 

 In the system BaO-Si02 the compounds BaO, 2BaO.Si02, BaO.Si02, 

 2Ba0.3Si02, Ba0.2Si02, and Si02 were found. Of these the dibarium tri- 

 silicate, 2Ba0.3Si02, and barium disilicate, Ba0.2Si02, showed remarkable 

 behavior, being isomorphous, of orthorhombic symmetry, and forming a 

 complete series of solid solutions without maximum or minimum in the 

 melting diagram. The indices of refraction show continuous though not 

 linear variation with the composition. The barium metasilicate is not iso- 

 morphous with calcium and strontium metasilicates, being probably ortho- 

 rhombic. It forms, with CaO.Si02, a double compound, 2CaO.Ba0.3Si02, 

 which melts incongruently, breaking up into a-Ca0.Si02 and liquid. It is 

 optically uniaxial and negative. 



Neither strontium nor barium metasilicate forms, with magnesium metasili- 

 cate, a double compound analogous to diopside, CaO.Mg0.2Si02. This is 

 considered as a special case of the more general rule that calcium, in those 

 compounds in which it can be replaced by magnesia and ferrous oxide, can 

 not be replaced by strontia or baryta, while the isomorphous series including 

 strontium or barium compounds may have isomorphous and miscible analogs 

 among sodium, potassium, or lead compounds. 



Both strontium and barium form feldspars. The strontium feldspar, 

 SrO.Al203.2Si02, has indices of refraction exactly hke those of anorthite, 

 and the two seem to be completely miscible. The barium feldspar, 

 BaO.Al203.2Si02, is monoclinic and like the natural celsian, which is known 

 to be isomorphous and miscible with orthoclase. 



Calcium, having the lowest atomic weight among the so-called alkaline 

 earth elements, forms the basic silicates 3CaO.Si02 and 3Ca0.2Si02, the 

 analogs of which were not found among the silicates of strontium or barium. 



