STUDENTS' POTENTIOMETER OUTFIT As Used in Hydrogen Electrode Work T This outfit is completely described in our new Bulletin HE importance of the Potentiometer.in Electrical Measurements and in their various applications to scientific work can hardly be over-emphasized. Electromotive force is frequently a function of some other quantity under investigation-and the Potentiometer method is the standard way of measuring electromotive force accurately. Instruction in its use and principles is therefore an essential part of the training of the student of science. The students' Potentiometer Outfit, illustrated above, is admirably suited not only for instruction in the theory and use of the Potentiometer, but also for making accurate measurements of electromotive forces of various kinds of sources. It is simple of construction, dependable in operation, and its accuracy compels the respect of the student for the Potentiometer method. The cost of the outfit, not including batteries, switch or glassware, is $158.00. LEEDS & NORTHRUP COMPANY Electrical Measuring Instruments 4901 Stenton Avenue PHILADELPHIA, PA. RECENT MCGRAW-HILL JUST OUT BOOKS Geology of the Non-Metallic Mineral Deposits By AMADEUS W. GRABAU, S.D., Formerly Professor of Paleontology, Columbia University This book is essentially a treatise on applied stratigraphy. The emphasis is laid upon the geological relationships of salt deposits, including nitrates, phosphates, borates, and similar deposits. This first volume is devoted to a study of deposits now forming or which have but recently been formed, and of the physical conditions which control such deposition. The second volume, now in press, applies the principles previously discussed and analyzes the conditions under which the older deposits were formed. Introduction to General Chemistry By HERBERT N. McCoy, Ph.D., Consulting Chemist; formerly of the Department of Chemistry, University of Chicago, and ETHEL M. TERRY, Ph.D., Assistant Professor of Chemistry, University of Chicago. 648 pages, 6 x 9, 128 illustrations, $3.00 net, postpaid. A new course in freshman chemistry that is refreshingly original in arrangement and method. The book presents the work as the authors have gradually evolved it in their classes in the University of Chicago. In the words of one teacher, "Though the discussion is simple, it is accurate and up-to-date. The treatment of each principle is sufficiently extended to carry the student past the stage of passive observation to at least a moderate independence in the use of the material presented. In brief, McCoy and TERRY may be recommended as exceptionally well adapted to freshmen."' Principles of Animal Biology McGraw-Hill Agricultural and Biological Texts By A. FRANKLIN SHULL, Associate Professor of Zoology, University of Michigan, with the collaboration of GEORGE R. LA RUE, Assistant Professor of Zoology, and ALEXANDER G. RUTHVEN, Professor of Zoology and Director of Museum and Zoology, University of Michigan. 441 pages, 6 x 9, 245 illustrations, $3.50. The book aims to present a body of principles that may be brought under such topics as morphol ogy, physiology, ecology, taxonomy, geographical distribution, paleontology and evolution. It presents a general course covering the whole field of animal biology broadly, rather than a "type course. It discusses classification and morphology of types but only as these subjects fit themselves into the principles of the science of zoology as a whole. Microscopic Examination By W. MYRON DAVY and C. MASON FARNHAM. 154 pages, 6 × 9, illustrated, $2.50 net, postpaid. This book describes the latest methods in use for polishing, examining, testing, and photographing surfaces of minerals, ores and mill or smelter products. It also includes thoroughly tested determinative tables whose use makes possible ready identification of the ore minerals on a polished surface under the microscope; also tables of the most useful blowpipe and simple chemical tests. Send for copies of these books on approval MCGRAW-HILL BOOK CO., INC. 239 WEST 39TH STREET NEW YORK Molybdenum Wire Molybdenum Wire is a product of the General Electric Company's Research Laboratory. Because of its resistance to chemical action Molybdenum Wire is capable of many uses in the industries. It is particularly adaptable to use as a heating element in muffle furnaces. The chemical properties are as follows: Slowly dissolves in hydrochloric acid at 110° C. It is not attacked by dilute sulphuric acid Dissolved slowly by concentrated nitric acid Not attacked by hydrofluoric acid Not attacked by potassium hydroxide but is soluble in fused alkali Metal becomes coated after a time in acids, with an acid resisting oxide This wire can be furnished in standard diameter, .010" to .060". The melting point of molybdenum is approximately 2500° C. with oxidation occuring at red heat. Its resistivity at 20° C. is 4.1 microhms per centimeter cube and the temperature coefficient per degree between 0 and 170° C. is 005. For further details write our Schenectady (N. Y.) office General Electric General Office Company Schenectady, NY Sales Offices in 35B-22 FRANKLIN HIGH GRADE ANALYTICAL FILTER PAPERS for the Analytical Laboratory and Chemical Industry No. 616."Qualitative"-Special grade for accurate qualitative analysis; of great resistance; can also be used to advantage for filtering thicker liquids such as oils, extract, etc.; filters quickly and effectively. Diameter Price per 100 filters... 9 cm. $0.18 11 cm. $0.25 No. 660."Rapid Clearwell"-A filtering paper of very close texture and the highest retentivity; yields perfectly clear filtrates where other papers fail; specially suitable for analysis, polarisation, refraction, biological reactions; retains barium sulfate, calcium oxalate, gypsum, animal charcoal, clay, albumen, etc. No. 640."Goldlabel Ashless"-Treated with hydrochloric and hydrofluoric acids, filters rapidly and retains fine precipitates. Our Goldlabel Ashless brand of filter paper has the smallest ash weight of any double treated filter paper and represents a distinct advance in the art of preparing such papers. Diameter Price per 100 filters.... 9 cm. $1.50 In Stock for Immediate Delivery! WRITE FOR SAMPLES. 11 cm. ROHDE LABORATORY SUPPLY CO. High-grade Apparatus and Specialties for the Laboratory 17 Madison Ave. $1.80 NEW YORK Leitz Microscopes are the Standard of the World MICROSCOPE STAND “AA” It is especially recommended for Research Investigations and Micro Photography. For this purpose stand "AA" has been selected as standard by the leading laboratories of the U. S. Government, the Hospitals, Universities and Industrial Institutions throughout this and other countries. The mechanical construction is of utmost rigidity and every part of its adjustment of thorough precision. Leitz Apochromatic Objectives are individual in Quality and their Optical Efficiency embodies the very latest achievements in optical science, as developed by Leitz Research and Micro Photo- the Leitz Research Department. graphic Microscope "AA", outfit 30, with complete substage illuminating apparatus "a", and three-lens condenser N.A. 1.40, triple nosepiece, apochromatic objectives 16mm, 4mm, oil immersion 2mm, N.A. 1.32, compensating eyepieces No. 6 and 12, in mahogany cabinet. The Leitz Apochromats excel in Range of numerical aperature Color correction |