CADMIUM STANDARD CELLS For use with potentiometers, electrometers, and ballistic galvanometers, 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, a three having the same value. On March 30 1930, 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. 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. 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. The Rubicon Standard There is a little group of Engineers and Physicists in Philadelphia working to produce Physical and Electrical measuring instruments of the most exact precision, and of superlative quality. This organization was established sometime ago by men with many years' experience in the design, manufacture and use of precision instruments, and the equipment covers all machinery and electrical apparatus necessary for developing and standardizing to the highest precision. And along with their scientific fitness for the work they undertake, these men are just a bit old-fashioned in their business policies; old fashioned in that they handle orders promptly, accurately, courteously; old fashioned in believing that such treatment, coupled with rational, old fashioned charges, is the customer's due. This little group is known as RUBICON COMPANY Laboratory and Student Microscope "L 10" DEDEDERERER Leitz Microscopes are the LEITZ LABORATORY AND STUDENT A Student Microscope is naturally subjected to hard usage and in order to withstand severe handling, its workmanship has to be durable beyond question. The Leitz Laboratory and Student Microscopes embody the same high standard of optical and mechanical workmanship, so strongly identified with Leitz products, and are guaranteed, therefore, to serve in student laboratories in a more satisfactory manner than any others. The "Leitz-Quality" is beyond comparison, and since it is unequalled, it is supreme. Optical and Mechanical Efficiency are the chief points expected of any microscope; the Leitz instruments are recognized to possess these standards to a non-contestable degree. Write for Pamphlet No. 0-1001 Announcing A New Selected List of LANTERN SLIDES For Physics, Mechanics, Heat, Sound, Light, We have prepared a new set of lantern slides for physics departments containing some new material and some very fine illustrations demonstrating in a very clear manner the fundamental laws of physics. The number of slides is not large. They have been limited in number purposely, but the set covers the entire field of the subject matter of physics. This insures a better balanced set than an equal number selected from a larger list. Most of these slides have more than one view on each slide. The average number is approximately three. Many of them have five or six views. This puts the maximum value in each slide at a minimum cost. The material is especially selected. Many of the drawings and illustrations have been made specifically for this purpose, and others selected from the most effective illustrations from various sources. Send for Illustrated Descriptive List and Prices. OTHER SLIDE SETS FOR AGRICULTURE, BIOLOGY, ETC. W. M. Welch Scientific Company Manufacturers, Exporters, Importers of Scientific Apparatus and Supplies 1516 Orleans Street Chicago, Ill., U. S. A. Stanrd University, Cal Prof Ellwood P. Cubberle ADIMEN! EDUCATION MAY REE PRINTINGS SHINOW OF TAREE yes the theory, lands, the syPORD detaleuSITY This work is a complete record of today's endocrine knowledge Burton-Opitz's Physiology Cloth, $7.00 net REPRINTED IN This new work is arranged logically; it is brief and simple in style; there are many Octavo of 1158 pages, with 538 illustrations, many in colors. By RUSSEL BURTON-OPITZ, M.D., Associate Professor of Burton-Opitz's Laboratory Physiology This is, in a sense, a companion volume to the author's "Text-Book of Physiology," Drew's Invertebrate Zoology Cloth, $4.00 net, THIRD Professor Drew's book gives you a working knowledge of comparative anatomy and an appreciation of the adaptation of animals to their environments. Cloth, $2.25 net 12mo of 239 pages. By GILMAN A. DREW, PH.D., Assistant Director of the Marine Biological Laboratory, Woods Hole Mass. Mallory and Wright's Pathologic Technic SEVENTH This work gives the technic of bateriologic methods, bacteriology of various diseases, Octavo of 555 pages, with 18 illustrations. By FRANK BURR MALLORY, M.D., Pathologist to the Boston City Hospital, W. B. SAUNDERS COMPANY, West Washington, Sq., Phila. SIGN AND MAIL THIS ORDER FORM TODAY |