CADMIUM STANDARD CELLS For use with potentiometers, electrometers, and ballistic galvanometers, or wherever else a precision standard of electromotive force la needed. Negligible Temperature Coefficient. Highly Constant E. M. F. Contents hermetically sealed in glass so that lowering of electromotive force due to evaporation is impossible. Mounted in moulded box, or unmounted. My comparison certificate accompanies each cell without charge. On November 13, 1916, three normal cadmium cells made by me were certified by the Bureau of Standards as differing from their group of reference cells by less than one part in one hundred thousand, all three having the same value. On March 30 1920, after the lapse of three years and four months, the same three cells were again compared by the Bureau of Standards. The maximum difference among the three was less than one part per hundred thousand, and the maximum difference from their certifed value of 1916, was less than one part per hundred thousand. In other words, these cells showed a degree of constancy to all intents equal to that considered most highly satisfactory, if not remarkable, in the very best type of precision resistance standards. (see Bul. Bur. of Stand. Vol. 5, No. 3, p. 427.) The cells in question were in nowise special. They were made of the materials regularly prepared by me, and were set up with no greater care than that constantly employed in the making of my standards. Marion Eppley, (A.M., Ph.D.) Physico-Chemical Apparatus. NEWPORT, R. I. No Laboratory Equipment is complete without some variable resistances. To maintain the high standard of your outfit we suggest the addition of some "Becbro" Sliding Contact Rheostats (Tubular and Stone Types) Thousands of these rheostats have been manufactured and sold by us (the original American Manufacturers) to most all Universities, Colleges, Technical Schools and Industrial Concerns and have always given entire satisfaction. Write for Bulletin C-5 BECK BROS. 3640-42 North Second Street Philadelphia, Pa. 150902 HIGH VACUUM PUMPS Whenever in lecture-room or laboratory practice, really high vacuum is required, we recommend the Condensation Pump developed by Dr. Irving Langmuir of the General Electric Companybelieving it to be superior to any other as yet obtainable. The Langmuir Pump operates with surprising rapidity, and there seems to be no practical limit to the degree of exhaustion that can be produced. Some form of auxiliary pump must be used; and for that purpose we offer a special G. E. two-stage oil-sealed mechanical pump, which is capable of producing a vacuum of 0.001 mm. when used alone. The picture shows a complete outfit comprising Langmuir Condensation Pump, two-stage auxiliary pump and 1⁄2 H.P. motor-all mounted together on one base. Write for descriptive bulletin S-965 JAMES G. BIDDLE 1211-13 Arch St. Philadelphia Eastman Organic Chemicals SINCE the issue of our price list in March, the following chemicals have become available: Of the above list all those distinguished by an asterisk have been prepared or purified in our laboratory. xiii X. Aquaria. We have been handling Natural History Material of all kinds for the past fifty years, and so have accumulated a very complete stock. Our prices are as low as the quality of the specimens will permit. We are constantly preparing circulars and price lists covering our material in the different branches, which we will be pleased to send free of charge to the readers of Science. Some of our recent circulars: S-119 Cretaceous Fossils CONCHOLOGY GEOLOGY "Oliver Asking for More", by George The Masters' Approval Since 1771 the world's great masters This craftsmanship, which has produced All the experience and accomplishment WHATMAN Grade Chemists who are unacquainted with their present excellence should make a comparative test. All dealers in laboratory supplies carry these papers in stock Samples will be supplied on request H. REEVE ANGEL & CO. INCORPORATED 7-11 Spruce Street New York, N. Y. Sole Mill Representatives for the United States, Canada and Mexico 6 NEW SERIES VOL. LIII, No. 1371 FRIDAY, APRIL 8, SINGLE COPIES, 15 CTS. New Blakiston Books COLLIS AND GREENWOOD. The Health of the Industrial Worker. 38 Illustrations. Octavo. Cloth, $7.00 Postpaid. By EDGAR L. COLLIS, M.D., M.R.C.P., Professor of Preventive Medicine, Welsh National School of Medicine; and MAJOR GREENWOOD, M.R.C.P. (Lond.), Member Industrial Fatigue Research Board, London; With Chapter on Reclamamation of the Disabled by ARTHUR J. COLLIS, M.D., Medical Superintendent, Ministry of Pensions Hospital (England), and an Introduction by GEORGE NEWMAN, K.C.B., M.D. (Lond.). HOOD AND CARPENTER. Textbook of Practical Chemistry. With 162 Illustrations. 8vo. xii + 527 pp. Cloth, $5.00 Postpaid. By G. F. HOOD, M.A. (Oxon), B.Sc. (Lond.), Chemistry Master Nottingham High School; and J. A. CARPENTER, M.A. (Oxon), Major, Late Science Master, St. Paul's School, and Lecturer in Physics, Royal Dental Hospital, London. MCGUIGAN. An Introduction to Chemical Pharmacology. Pharmacodynamics in Relation to Chemistry. By HUGH MCGUIGAN, Ph.D., M.D., Professor of Pharmacology, University of Illinois College of Medicine. 8vo. xii + 418 pp. Cloth, $4.00 Postpaid. AUTENRIETH. Laboratory Manual for the Detection of Poisons and Powerful Drugs. SMITH. Priestley in America, 1794-1804. An Account of the Life and Work of the Dis- MOLINARI. General and Industrial Organic Chemistry. Part I. Cloth, $8.00 Postpaid. By ETTORE MOLINARI, Milan; Translated by T. H. POPE, B.Sc., University of Birmingham (Eng.). SCHNEIDER. The Microanalysis of Powdered Vegetable Drugs. 2d Edition. 237 Illustrations. 8vo. Cloth, $5.00 Postpaid. By ALBERT SCHNEIDER, M.D., Ph.D., Professor of Pharmacology, College of Pharmacy, University of Nebraska. P. Blakiston's Son & Co., Publishers, Philadelphia |