138 CARNEGIE INSTITUTION OF WASHINGTON. 



in alumina. The obsidian is much like pantellerites of Italian volcanoes. The 

 result was quite unexpected and is of interest, as it points to the existence of 

 an occurrence of such highly sodic lavas at some point in southern Mexico or 

 northern Central America which is as yet unknown. The occurrence of this 

 rock type emphasizes the need for fuller study of the igneous rocks of Mexico 

 and Central America, about which little is known. 



The refractive indices of the two obsidians were determined by Dr. H. E. 

 Merwin. They conform to the general rule observed by Merwin and the 

 author in the study of other obsidians at Lipari, Milos, and elsewhere. 



(433) Note on the dissociation of ferric oxide dissolved in glass and its relation to the color 



of iron-bearing glasses. J. C. Hostetter and H. S. Roberts. J. Am. Ceram. 

 Soc, 4, 927-938. 1921. (Papers on Optical Glass, No. 39.) 



Data presented here show that ferric oxide partly dissociates on heating in 

 air, giving off oxygen and forming a corresponding amount of ferrous oxide. 

 The formation of this lower state of oxidation takes place under what are 

 ordinarily considered oxidizing conditions and is to be carefully distinguished 

 from reduction by such gases as hydrogen and carbon monoxide. It is also 

 shown by analyses and color studies that ferric oxide dissolved in glass disso- 

 ciates in a similar manner, forming ferrous iron, under oxidizing conditions. 

 The degree of dissociation is dependent upon the composition of the glass and 

 probably varies over a wide range as the ratio of alkalies and other constitu- 

 ents of the glass are changed. The data given are insufficient to warrant 

 sweeping conclusions, but further studies along the lines indicated may explain 

 certain observations on color and absorption in relation to chemical com- 

 position in iron-bearing glasses. 



(434) The lavas of the Hawaiian volcanoes. Henry S. Washington. Hawaiian Annual 



for 1922, pp. 39-49. 



The paper points out briefly some of the characters of the lavas, what they 

 mean and what they may teach as to the constitution of the earth, especially 

 from the chemical side. The paper is written in "popular" style. 



(435) A mathematical note on the annealing of glass. E. D. Williamson. J. Wash. Acad. 



Sci., 12, 1-6. 1922. (Papers on Optical Glass, No. 41.) 



From the equations representing the results of experimental work, pre- 

 viously described, the most favorable conditions for annealing a given piece of 

 glass are deduced. Formulas are found which, used in conjunction with 

 tables of the elastic and annealing constants of the glass, show at what tem- 

 perature to hold the glass, how long to hold it at that temperature, and how 

 rapidly to cool it in order to get any degree of fineness of annealing in the leas 

 possible time. Examples are solved to illustrate the processes. 



(436) Augite of Haleakala, Maui, Hawaiian Islands. Henry S. Washington and H. E. 



Merwin. Am. J. Sci., 3, 117-122. 1922. 



The optical and chemical data of a typical augite of an Hawaiian lava are 

 given, this being the first analysis made of an Hawaiian augite. It closely 

 resembles augites from other basalts and is composed chiefly of diopside and 

 hedenbergite, with a little acmite and alumina. The authors reject the view 

 of the existence of Tschermak's molecule, as well as those of Boeke and Zam- 

 bonini, to account for the presence of alumina in such augites, and assume 

 that the alumina and ferric oxide are present as such in solid solution with 

 the pyroxene molecules. The bearing of an outer film that is high in ferric 

 oxide is briefly discussed. 



(437) The crystal structure of ammonium chloroplatinate. Ralph W. G. Wyckoff :;nd 



Eugen Posnjak. J. Am. Chem. Soc, 43, 2292-2309. 1921. 



Crystals of ammonium chloroplatinate ((NH^PtCle) probably have a 

 structure which is analogous to that commonly assumed for fluorspar if PtCU 



