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INDUSTRIAL AND ENGINEERING CHEJIISTRY
VOL. 10, NO. 11
formly satisfactory physical condition in spite of maintenance of constant or substantially constant weight throughout the observation period.
diet supplemented with pure entities or proved concentrates as the source of other dietary essentials.
Summary
Literature Cited
On t h e basis of the d a t a submitted, especially when appraised in comparison with the performance and response of groups of animals submitted t o similar tests b u t Tvith less control and standardization of t h e dietary components and supplements, it appears t h a t the vitamin B1 determination involving the specificity of the polyneuritic reactions m a y be standardized by employing a comparatively simple basal
(1) Bender, R. C., and Supplee, G. C., J . A m . Chem. Soc.. 59, 1178 (1937). ( 2 ) Chase, E. F., and Sherman, H. C., I b i d . , 53, 3506 (1031). (3) Smith, 11.I., G. S.Pub. Health Rpts., 45, 116 (1930). (4) Yteenbock, H., and Nelson, E. M., J . B i d . Chem., 56, 355 (1923). (5) Waterman, R. E., and Ammerman, hl., S. A\r'utrition, 10, 35 (1935). RECEIVEDAugust 1, 1938.
A Glass-Enclosed Magnetic Stirrer J. H. SI3lOKS The Pennsylvania State College, State College, Pa.
S
TIRRISG within a n enclosed glass system is frequently desired and usually accomplished b y means of a magnetic device. T h e diagram shows a design which has proved very satisfactory. The stirrer contains a sealed-in iron core and is
supported on glass bearings. T h e rotor which motivates it consists of a brass tube running in ball bearings and ca,rrying;a system of electromagnets. This is rotated by a small electric mot or. The glass tube, J , carrying side tubes for the admission of materials, has a small reentering tube, D, at the top for a bearing and at the bottom has a larger reentering tube terminating in a small fire-polished button that forms the lower bearing and supports the iveight of the stirrer. The seals holding these bearing tubes must be smooth and well rounded. The stirrer has an open tube at the top into n-hich the top bearing enters. Below that a larger tube contains the iron core, M , 0.6 cm. (0.25 inch) thick, which is Hshaped and is made of soft iron lamina riveted together. The shaft, made of 6-mm. tubing, is connected to the bottom of this larger tube, and terminates at the loiTer end in an inverted cone, N . The rim of this cone is thickened and to it are attached two rods, which are twisted and sealed to a ring of glass at the bottom to form the agitator, P. Tube J is made in two parts. The stirrer shaft is encased in copper screen or gauze and placed in J . The final seal can then be made without bending the shaft, and the copper is removed with nitric acid. The magnets, E, are made of rectangular brass bobbins wound with No. 18 B. & S. insulated copper \Tire. The core, I , is of soft iron lamina which is 0.6 cm. (0.25 inch) thick through the central magnets and 0.3 em. (0.125 inch) thick through the outer ones. This core enters slots in the wall of the brass tube, K . Brass disks above and below the magnets are securely fastened to the bobbins. The frame is made of four 1.25-cm. (0.5-inch) brass rods about 75 em. (2.5 feet) long, held with three pieces of 0.3-cm. (0.125-inch) boiler plate, H , 17.5 X 17.5 cm. (7 X 7 inches). The bottom and middle plates are securely fastened, but the top plate is held with nuts to enable the magnet assembly to be removed. The brass tube, K . 5 em. (2 inches) in diameter, rests on a thrust ball bearing, F , and has a 1.25-cm. (0.5-inch) brass shaft at the top, which is guided by the ball bearing, C. Insulated rings of brass, G, make electrical contact with carbon brushes connected to the magnets. The rotating assembly is carefully balanced to eliminate vibration. The motor support, B , contains clamps with rhich to secure the motor, A . This is a small inexpensive constant-ppeed motor with reducing gears. Motors of a great variety of speeds can be obtained, and changing the speed of stirring is accomplished by changing the motor.
A magnetic stirrer of this design has been very useful in studying the chemical reactions of small quantities of valuable gases. The ini-erted form of t'he lower bearing, iV,prevents solid materials from interfering with the rotation. T h e reentering tube with rounded seal resists thermal shock, and the tube withstands being plunged into liquid air. Mechanical strength is good, and the device has been used with internal pressures up t o five atmospheres. RECEIVED July 26, 1938.
