A Sign of Quality WELCH from a House of S No. 905 UNIVERSAL MOTOR ROTATOR. This rotator has been designed especially for and laboratory use. The motor will run on either A.C. or D.S. of 110 volts. The speed m varied from a few revolutions per minute to 1,500 R.P.M. The speed changes are continuous in steps-and speed is changed by simply turning a thumb screw. The holder for the acce is standard form and size and will hold all commonly used accessories. A chuck is included the instruments for holding discs, etc. The position of the rotating shaft may be made horiz vertical or any intermediary position and may be held firm any of the positions. The use of the friction disc eliminat jerkiness of starting and running. The motor is especially ad for the purpose and is very powerful and will pull any acce at full speed. A stop is provided so that excessive speeds a possible, although sufficient speed is provided for to opera rotator accessories. A speed counter is mounted so that the 1 may be determined where quantitative work is required. entire apparatus is about 30 cm. long, 15 cm. wide and 20 cm. Handsomely finished in black enamel and nickel-plated trimr Complete as described with 6 feet of cord and detachable pli connection. W. M. WELCH SCIENTIFIC COMPAN MANUFACTURERS, IMPORTERS AND EXPORTERS OF SCIENTIFIC APPARATUS 1516 ORLEANS STREET CHICAGO, ILL., U. We shall be pleased to send to science departments of schools outside of the United our especially prepared catalogue for foreign circulation only. A request giving your officia tion is all that is necessary in order to receive this catalog. STUDENTS' POTENTIOMETER OUTFIT As Used in Hydrogen Electrode Work THE This outfit is completely described in our new Bulletin HE importance of the Potentiometer in Electrical Measurements and in their various applications to scientific work can hardly be over-emphasized. Electromotive force is frequently a function of some other quantity under investigation-and the Potentiometer method is the standard way of measuring electromotive force accurately. Instruction in its use and principles is therefore an essential part of the training of the student of science. The Students' Potentiometer Outfit, illustrated above, is admirably suited not only for instruction in the theory and use of the Potentiometer, but also for making accurate measurements of electromotive forces of various kinds of sources. It is simple in construction, dependable in operation, and its accuracy compels the respect of the student for the Potentiometer method. The cost of the outfit, not including batteries, switch or glassware, is $158.00. LEEDS & NORTHRUP COMPANY Electrical Measuring Instruments 4901 Stenton Avenue PHILADELPHIA, PA. iv Invention Anticipates Necessity The research laboratory of the General Electric Company at Schenectad is dedicated to the electrical industry. Its facilities for scientific research, almost coextensive with the scope of ele trical industry itself, surpass in variey and extent the equipment of universi laboratories. Scientific experimentation proceeds hand in hand with the development new devices and new methods of manufacture. The result of this industri research-the cooperation of science and industry-is first, the increase scientific knowledge, and second, the embodiment of this increment in bett materials and new devices which ultimately make happier and more livab the life of all mankind. General Electric General Office Company Sales Offices in 86-144 DIFCO RARE SUGARS and OTHER FINE CHEMICALS "DIFCO" STANDARDIZED Being the first manufacturing firm in the United States to make and advertise extensively rare sugars, we have steadily added to the line, and our list now comprises the following: Carried in stock by the principal dealers in Scientific Supplies Digestive Ferments Company Detroit, Michigan, U. S. A. vi Co-ordinating Our Labor with Yours Kewaunee Laboratory Furniture is the most scientifically planned and thoroughly constructed that has yet been produced. It has been the supreme effort of our business life to co-ordinate our labors with yours in the school room, in an endeavor to raise the standards of cleanliness, economy of time and general efficiency among your young people. Physics Laboratory Table No. 700, our best seller in this line. Deservedly pop- We feel sure that Kewaunee Equipment justifies words like the following from a Californi Science specialist: "It gives me pleasure to testify to the very superior quality of your laboratory furniture In every respect-design, material, workmanship, and finish-it merits the highost com mendation. The Kewaunee Book will help you solve the laboratory problems of your school. A dress all inquires to the factory at Kawaunee. New York Office CHICAGO Kewaunee Mfg. Co. LABORATORY FURNITURE 115 Lincoln Street KEWAUNEE. WIS. BRANCH OFFICES: KANSAS CITY 70 Fifth Avenue SPOKANE SAN FRANCIS |