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is used by thousands of Schools all over America. It is selected where the highest educational standards in equipment are observed. If interested in equipment for Physics, Chemistry, Biology, Agriculture, Electricity, Domestic Science or Art, Manual Training or Kindergarten work in your school-ask for the Kewaunee Book. It is free. Address all inquiries to the factory at Kewaunee.

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Our Laboratory Spectrometers

Are sold in competition with instruments of European make

to many of the best laboratories throughout the world. WM. GAERTNER AND CO.

Physical and Astronomical Instrumonts 5345-49 Lake Park Avenue

CHICAGO

Eastman Organic Chemicals

DURING the past month the following chemicals have

become available:

981 * d-Bromopropionic Acid
977 * d-Bromo-n-valeric Acid
980 Dichloroacetic Acid
978 * Diphenylhydrazine
995 * Ethyl Bromoacetate
994 * Ethyl d-Bromo-n-butyrate
988 * Ethyl d-Bromo-n-valerate

973 Ethylene Bromohydrin
976 Ethyl Lactate
982 * 5-Methylbenzoxazole
993 * Methyl m-Nitrobenzoate
979* p-Nitrophenylhydrazine HCl.
989 * Triphenylchloromethane
975 * Undecylenic Acid

Of the above list all those distinguished by an asterisk have been prepared or purified in our laboratory.

EASTMAN KODAK COMPANY
RESEARCH LABORATORY

ROCHESTER, N. Y.

NEW SERIES
Vol. LIII, No. 1376

FRIDAY, May 13, 1921

SINGLE COPIES, 15 Cts.
ANNUAL SUBSCRIPTION, $6.00

New Blakiston

boks

Palo Alto Calit
John F. Newgom,

1129 Cowper Street,

OOLLIS AND GREENWOOD. The Health of the Industrial W

Illustrations. Octavo. Cloth, $7.00 Postpaid. By EDGAR L. COLLIS, M.D., M.

fessor of Preventive Medicine, Welsh National School of Medicine; and MAJO

QOD, M.R.C.P. (Lond.), Member Industrial Fatigue Research Board, London; W

on Reclamamation of the Disabled by ARTHUR J. COLLIS, M.D., Medical Supe

Ministry of Pensions Hospital (England), and an Introduction by GEORGE N

T.C.B., M.D. (Lond.). HOOD AND CARPENTER. Textbook of Practical Chemistry. W.ca 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.

5th Edition. Revised. 25 Illustrations. 8vo. XV + 342 pp. Cloth, $3.50 Postpaid. By DR. WILHELM AUTENRIETH, Professor in the University of Freiburg; Authorized

Translation by WILLIAM H. WARREN, M.D. SMITH. Priestley in America, 1794-1804. An Account of the Life and Work of the Dis

coverer of Oxygen while in America. 16mo. v + 173 pp. Cloth, $1.50 Postpaid. By

EDGAR F. SMITH, University of Pennsylvania. COPAUX-LEFFMANN. Introduction to General Chemistry. 30 Illustrations. 12mo,

x + 195 pp. Cloth, $2.00 Postpaid. By H. COPAUX, Professor of Mineral Chemistry, School of Industrial Physics and Chemistry, Paris. Translated by and with Appendix by HENRY LEFFMANN, A.M., M.D., Member American Chemical Society and of the British

Society of Public Analysts. An exposition of the principles of modern chemistry. BARNETT. A Textbook of Organic Chemistry. Illustrated. Cloth, $5.00 Postpaid. By

E. DE BARRY BARNETT, B.Sc. (Lond.), Lecturer in Organic Chemistry, Sir John Cass

Technical Institute, London. 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 Birming

ham (Eng:). SCHNEIDER. The Microanalysis of Powdered Vegetable Drugs. 20 Edition. 237 Illus

trations. 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

Theory and Practice

TOLMAN
Theory of the Relativity

of Motion
With Appendix

MILLIKAN: Mechanics,
Molecular Physics, and Heat.
MILLIKAN and MILLS:
Electricity, Sound, and Light.

A supplement to this work, written by the
author, has just been issued. Under the
title,
Relativity Theories in Physics
this Appendix gives a general description
of the nature of relativity theories, to-
gether with brief discussions of Tolman's
theory of similitude or relativity of size,
of Einstein's theory of the relativity of
uniform motion, and of Einstein's theory
of gravity and general relativity.
ix + 242 pages (including Appendix).
Cloth, $1.75. Carriage extra. Weight,
154 pounds.

Appendix only (paper), 25 cents.
The University of California Press

BERKELEY, CALIFORNIA

These books provide for intimate correlation between classroom discussion and laboratory exercises. Together they constitute an up-to-date full - year course,

GINN AND COMPANY Boston New York Chicago London Atlanta Dallas Columbus San Francisco

A NEW WILEY BOOK Principles of Radio Communication

By J. H. MORECROFT
Associate Professor of Electrical Engineering, Columbia University

Assisted by A. PINTO and W. A. CURRY
NHIS BOOK deals with all phases of the Radio Art, going completely into

both theory and operation. The treatment is more thorough than is generally

given, and for this reason the book will have a wide appeal among workers in this field, the importance of which is so rapidly increasing.

The text of “RADIO COMMUNICATION” comprises 935 pages, 6 by 9 inches, and contains 788 illustrations, many of which are reproductions of oscillographic records of transient phenomena. All curves used to illustrate formulæ are carefully executed to scale and may be used as typical problems. The book is cloth-bound. $7.50 postpaid.

Enter Your Order for a FREE EXAMINATION Copy

JOHN WILEY & SONS, Inc. 432 Fourth Avenue

NEW YORK

PHYSICAL METHODS IN

LABORATORY ANALYSIS

It is a well-known fact that any measurement in any science involves the application of a physical method. The measurement may be mechanical, as with an analytical balance or a kymograph; it may be one of temperature or heat, as with a respiration calorimeter; it may be optical, as with a microscope, spectroscope or colorimeter; or it may be electrical, as of resistance, current or potential difference, any of which may have a definite, known relation to some biological characteristic that is being investigated.

Leeds & Northrup Company has long specialized in electrical measuring instruments and their applications. A recent activity has been the development of suitable instruments for measuring the potentials of a hydrogen electrode, in solutions and media, which correspond to hydrogen-ion concentrations or pH values.

The studies we have made on this subject are summarized in Catalogue S75, which gives a clear explanation of the principles involved in the measurements and describes how they are made. It also contains a representative bibliography of fifty titles, bearing on many scientific applications of the hydrogen electrode, and a descriptive price list of suitable electrometric apparatus. If you feel that the publication might be of service in your laboratory, we should be very glad to send you a copy gratis.

Leeds & Northrup Company

Electrical Measuring Instruments 4901 Stenton Ave.

Philadelphia, Pa.

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