Reading Device for Thermometers C1365, $4.00 Send for Catalog Our Laboratory Spectrometers WM. GAERTNER AND CO. Physical and Astronomical Instruments 5345-49 Lake Park Avenue CHICAGO VOCATIONAL CHEMISTRY For Students of Agriculture and Home Economics By JOHN J. WILLAMAN, Ph.D. Assistant Professor of Agricultural Biochemistry, School of Agriculture, 70 illustrations in text. 294 Pages. Price $1.75 net. Here is a valuable and practical book designed to fill the gap between the elementar chemistries written for students in city high-schools, and those written for either boy following agricultural courses or girls in home economics. The large number of so-calle agricultural high-schools coming into existence makes this new book by Prof. Willama particularly welcome. VOCATIONAL CHEMISTRY is especially adapted for mixed classe with no one-sided emphasis placed on either agriculture or home economics. A simple an practical exposition of all material that will be of interest and value to the boy and gi SCURVY PAST AND PRESENT By ALFRED F. HESS, M..D. New York. 275 Octavo Pages. Cloth, $4.00. Interest in scurvy has been stimulated in the last few years as the result of a new ar broader conception of nutrition. It is clear that the subject is merely in its infancy, a is destined to participate in a consideration of many of the nutritional and infectious di eases of the adult and the child. For the past seven years Dr. Hess has been engaged in a investigation of scurvy both in the laboratory and in the clinic, and has treated vario aspects of the subject in a large number of published articles. The time is opportune offer to the clinician, to the hygienist, and to the biological chemist, a presentation of t existing status of this important nutritional disease, as no work on scurvy has been pu lished in English since the classic work by Lind in 1772. This new work by Dr. Hess includes radiographs not to be found elsewhere and is most comprehensive and authoritative volume on the subject. American Medical MUSEUM JARS PATENTED The first rectangular Museum Jar made in America Made of perfectly clear and colorless glass, thoroughly annealed, so that all internal strains are removed. The corners and edges are thick. The possibility of breakage is therefore reduced to the minimum. The surfaces, inside and out, are polished planes, so there is no distortion of the object placed within. The tops of the jars are ground true and the reinforced edge provides a wide surface for tight sealing. Bottom surface is ground flat so that the jar sets firmly. The small recess at the top of the jar will hold a glass rod or frame to support the specimen. Covers are of the same quality of glass, are polished and correspond with the jar and are ground to fit perfectly. Made in eleven different sizes as adopted by the International Association of Medical Museums Write for Prices and Descriptive Circular Designed, Patented and Distributed by SCIENTIFIC MATERIALS COMPANY Everything for the Laboratory" CADMIUM STANDARD CELLS For use with potentiometers, electrometers, and ballistic galvano. meters, or wherever else a precision standard of electromotive force is needed. Negligible Temperature Coefficient. 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 certified 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. Type T. R. Single Tube Rheostat No Laboratory Equipment is complete without some variable resistances. To maintain the high standard of your outfit we suggest the addition of some 66 "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. Stanford University, Calif. SINGLE COPIES, 15 CTS. Vacuum Pumps No. 5681-No. as shown in cut, is for No. 1-2 size pump is used No. 2 is used with No. 1 to give vacua to 1/10000ooth of an inch. It requires 4 H. P. motor. Above pumps are compact, and require comparatively little power. They are easy and safe to operate. They are used for X-ray tubes, nitrogen. lamps, tungsten lamps, thermosbottles, rectifiers, also for general laboratory and lecture work. No. 3709-Columbia University Model, improved form of McLeod Vacuum Gauge mounted on oak board. This gauge is compact in construction, easy to operate, has no glass joints and is accurate to one ten-millionth of an atmosphere. The gauge is recommended for use with above pumps, and wherever exact determinations of vacua are required. 4. SA Columbia |