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105Diaspore and boehmite clays give curves' characteristic of t h e respective minerals.Burley clays give curves which appear t o be combinations of diaspore and kaolinite in the endothermic peak but do not show the exothermic (gamma alumina?) peak of kaolinite. The excess of alumina above the kaolinite composition may eliminate the exothermic peak below 1000°C. T h e clay from loess near McBaine, Missouri, the clay from a gumbotil zone (Kanshn drift) near Columbia, Missouri, and the clay colloid of the Putnam soil are beidellite.The differential thermal-analysis technique does not appear to be very sensitive in detecting small quantities of a clay productive of weak thermal response when naturally mixed with relatively large quantities of other clay. It may have t o be supplemented b y other determinative techniques before a correct clay mineral analysis can be reported. AcknowledgmentThe authors are indebted t o A. P. Green Fire Brick Company for the loan of their part of the differential thermal analysis apparatus used in making the analyses described in this report. They are appreciative of the help and courtesy of Ben K. Miller, Robert Turner, A. R. Lesar, employees of A. P. Green Fire Brick Company, and of the several refractories companies and clay shippers who generously offered clay samples and permitted collecting from their properties.

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Calcium aluminate glasses containing alkali oxides and iron oxide will transmit infrared radiation to about 6 p and still have satisfactory working properties. Their refractive index, density, expansion, Young's modulus, modulus of rupture, fracture velocity, Knoop hardness, and some electrical and chemical properties are evaluated.

Phosphorus pentoxide, which was used first to improve the color of heavy flint glasses, was later recognized as a valuable constituent of optical glasses, and the excellent ultraviolet transmission and low softening points of phosphate glasses have been found recently. Glasses that have a high content of PSOS have poor chemical resistivity, but this drawback is largely overcome by the addition of alumina. A possible picture of the constitution of phosphate glasses is presented, and the effect of alumina is explained. Some of the properties of the phosphate glasses have been investigated and correlated with their chemical composition and structure.