ALL ELECTRICAL RESISTANCE MEASUREMENTS WHICH COME WITHIN THE RANGE OF A WHEATSTONE BRIDGE, CAN BE MADE WITH A LEEDS & NORTHRUP TYPE S PORTABLE WHEATSTONE BRIDGE The set is self-contained, complete with battery and gal- Type S Set, on a 110-volt alternating current circuit, ELECTROLYTIC CONDUCTIVITY MEASUREMENTS can as readily be made as ordinary resistance measurements. Ask for Bulletin S530 LEEDS & NORTHRUP COMPANY ELECTRICAL MEASURING INSTRUMENTS 4901 STENTON AVENUE PHILADELPHIA, PA. Immediate Delivery. Write for our booklet on Blood Chemistry C. M. SORENSEN CO., Inc., Dept. K GENERAL DISTRIBUTORS 177 East 87th Street NEW YORK Laboratory Products for Experimental Use Among the many things developed in the interest of science or industry, by the General Electric Company's research laboratories at Schenectady, are to be had various little-known products, whose uses are so far purely experimental. Scientists and experimental bureaus can secure from the G-E laboratories Storage Batteries "Chloride Accumulators" and "Exide Batteries" Are thoroughly satisfactory for scientific work, which accounts for their being used in so many of the educational and research laboratories throughout the United States. If you are equipped, and after long service your "Chloride" battery needs some renewals; or if you contemplate a new installation we are ready to serve you. By arrangement with the factory we act as Special College Representatives and are prepared to furnish portable or stationary outfits, with any number of cells for current capacity from ampere to any maximum desired. May we send you catalog? To aid us in rendering good service, please state what your requirements are. JAMES G. BIDDLE 1211 ARCH STREET PHILADELPHIA Constant-Temperature Apparatus Dependable for Long, Continuous and Unattended Operation FREAS OVEN TYPE R No. 100 Size of oven inside, 12"x12"x12". Temperature range, from room to 175°C. Regulation, Freas Metallic thermo-regulator. Constant within one degree over long periods. ΟΙ Construction, heavy asbestos tran- Furnished with Special Ther- SIMPLICITY of operation, ease of regulation, constancy and general dependability are the reasons why FREAS Ovens have been adopted by the most important laboratories of the U. S. Government, the leading educational, scientific institutions and the most progressive manufacturing plants in the country. FREAS Ovens are made in several sizes and types. They are approved by the National Board of Fire Underwriters. They are strongly constructed and reliable to the utmost detail. They may be left in operation, unattended, for months at a time if required. For Sale by All Dealers in Dependable Laboratory Apparatus Sole Patentees and Manufacturers 8 Johnson The Thermo Electric Instrument Co., Newark, N. J., U. S. A. MAKERS ALSO OF THE THELCO LINE Spencer Mon-Objective Possess all the features of construction which experience has shown to be meritorious and advantageous. Among them is the one very distinctive feature which distinguishes the Spencer, viz: Convergent Eyepiece Tubes which avoids the excessive and false conception of perspective otherwise produced, giving a correct interpretation of the object under examination. Several models. 1920 Catalog sent on request Spencer Lens Company MANUFACTURERS OF Microscopes, Microtomes, Projection Lanterns, Photo- SPENCER BUFFALO |