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ELEMENTS of OPTICAL MINERALOGYAn Introduction to Microscopic Petrography

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Fourth edition by ALEXADrER N. WrNCHELL, University of Wisconsin and HORACE WINCHELL, YaleUniversity. Describes minerals whose optical qualities are sufficiently well-known to permit diagnosisby means of a microscope. The minerals, with special emphasis on their microscopic and optic identi-fication, are arranged according to a classification based on chemical composition and crystal structure.Supplemented by 427 excellent illustrations, this extensively revised book completely covers pertinentdata, and focuses attention on relevant developments in the field since 1933. January 1951. 551 pages.$12.50.

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INTRODUCTION to AGRICULTURAL BIOCHEMISTRYBy R. ADAmS DUTCHER, CLIFFORD 0. JENSON, and PAUL M. ALTHOUSE, allat Pennsylvania State College. Covers general intrbductory material,plant growth, and animal growth, and includes such important topics asfarm chemurgy, pesticides, biological oxidations, and the nutritional re-quirements of human beings and domestic animals. January 1951. 502pages. Illus. $6.00.

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