A Filtering Apparatus J. F. KING
AND
H. F. PRIEST, Williams College, Williamstown, 1Iass.
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SOME radioactive research in this laboratory, thoriumX i s used. It is separated from the supply of radiothorium by adding gaseous ammonia to a hot hydrochloric acid solution of radiothorium containing iron. The radiothorium precipitates with the ferric hydroxide, leaving the thorium-X in the supernatant solution. The gaseous ammonia must be added t o a hot solution of radiothorium to prevent the precipitation by the carbon dioxide from the air of a basic carbonate of thorium-X along with the ferric hydroxide.
from hot solutions, and also in adding reagents dropwise from a beaker.
A represents a rubber-covered clamp which can be adjusted by a screw, G, t o take a number of different sized beakers. B represents thumbscrews which can be used to regulate the positions of the stirring rod, the beaker, and the filter funnel. D is a 40-1 worm screw which allovis the beaker to be tilted by the thumbscrea., C, so slowly that a liquid can be poured from the beaker at rates d o m to 1 drop in 3 seconds. E is a coiled spring which holds the stirring rod against the lip of the beaker and moves the funnel support as the beaker is being tilted through an arc. The special advantages of filtering with this apparatugover the usual hand methods are: (1) The beaker and rod are held so firmly t h a t none of the precipitate is stirred up during the filtration. (2) The beaker can be kept hot with a small burner during the filtration. (3) The rate of filtration can be easily controlled by a slight turn of the thumbscrew, C, without stirring u p the precipitate. (4) The supernatant1solution can be decanted off to the last drop without carrying
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FIGURE 1. FILTRATION APPARATUS T o speed u p and simplify the filtration of the solution from the gelatinous precipitate of ferric hydroxide, a filtration apparatus, illustrated in Figure 1, was designed. The hot beaker is held by a clamp on a solid support, so t h a t the gelatinous precipitate settles t o the bottom of the beaker. During the filtration, the precipitate is not stirred up, as is the case when the beaker is jiggled by holding in the hand. T h e supernatant solution can be decanted off t o the last drop without carrying over into the filter the gelatinous ferric hydroxide, which so readily plugs u p the pores of the filter paper and slows down the filtration. This filtering apparatus has been found useful in a number of laboratory procedures in separating precipitates, especially
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FIGURE 2. MOTORATTACHMENT 418
JULY 15, 1940
ANALYTICAL EDITION
419
the DreciDitate over into the filter. ( 3 ) The DreciDitate can be tkoroighly n7ashed by decantation and still remain in the beaker. I n Figure 2 is shown a motor attachment t h a t eliminates all handwork in a filtration.
regulate the speed at which the beaker is tilted. F controls a slip coupling, held in position by the sprlng, 0, by means of which the beaker is set for the start of the filtering. This coupling can be disconnected and the filtering done by turning the thumbscrew, C. N is an adjustable counterweight to balance the weight of the beaker with its solution.
The thumbscrew, C, is moved from its position in Figure 1 to the one shown in Figure 2. I is a constant-speed synchronous motor (sold by Herbach and Rademan, Philadelphia), t o which is attached a 4.5-inch Dowmetal disk, M , which revolves a t a rate of one revolution per hour. L is a 0.625-inch drive wheel of rubber or neoprene controlled by the setscrew, R, which is used to
Inonths and has given complete satisfaction.
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The filtering apparatus has been in constant use for several The equipmerit is being dereloped for the market by the E. H. Sargent Company, Cllicago, 111.
Machine for Testing Dentifrice Abrasion RALPH W. SRIITH, Ste. Genevieve Lime Companq, Ste. Genevieve, RIo.
This paper describes the design and operation of a machine for running production control tests on the abrasiveness of precipitated calcium carbonates. The machine is also used for testing dentifrices to determine if their abrasiveness is sufficiently low to class them as safe. Numerous test series indicate that the machine is sensitive, dependable, and accurate within the limits necessary for its purpose. Its special advantages are described and other uses are suggested.
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HE machine described here was designed primarily for
plant production control t'ests on the comparative abrasiveness of precipitated calcium carbonates, U.S. P., and for such uses it must be accurate, sensitive, rapid, and easily operated. A study of numerous existing machines (and papers relating n-holly or partially t'o the subject) indicated t h a t it was difficult t o build a machine on which duplicate abrasion results could be obtained. Other experimenters (11, 12) state: The development of a test suitable for finer powders, which requires an inert abraded surface giving loss large enough to be weighed or estimated chemically while the feed of an abrasive material is maintained steady and the bearing area is controlled, is more difficult . . . The method of feeding the plate with a suitably thin film of the suspension under the test is the most essential part of the present apparatus . . . Reproducible results could be obtained only if a certain somewhat critical film thickness is fed to the plate . . If too much suspension passes it causes abrasion only of the far edge, whilst with too thin a film the plate runs unsteadily and again a small loss is obtained. Altliough disks (silver and glass) were run in group each table, the losses were not uniform for the indi Repeat tests did not give the same relative amounts of loss.
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In the machine just referred to ( 1 1 ) a much larger antimony or metal surface v a s used (3 X 3 . i 5 em., 2 x 1.5 inches) than the one described in this paper (4.5 X 12 mm.) and a t times the larger antimony block became convex or concave. The m i t e r believes the considerable difference in speed of rulhing and total rubbing distance betn-een the inner and outer edges of the antimony specimen with the larger surface caused the concave or convex abrasion. Comparing the speed of rubbing contact and total travel distance during the test, the extreme variation between the inner and outer edges on the large specimen was 21 per cent, whereas the variation with the much smaller specimen was only 3 per cent. Later
modifications in this apparatus have apparently overcome some of these difficulties and have also improved the ease of working ( I O ) . The machine here described (using the small specimen) is not easily affected by film thickness, nor is t'here a lack of abrasion uniformity on the edges of the metal specimens. A series of about 500 tests indicates t h a t this machine is not easily affected by operation or manipulation conditions except variations in the abrasive characteristics of the materials tested.
METHODOF
Abrasion Jlachine DRIVE. A constant-speed, governor-controlled,
vibrationless dictaphone motor (2, Figure 1) is used for driving the machine. Copying the design of other similar machines, a worm-and-gear direct drive from the motor to the first counter shaft was used at first, but this produced vibration which not only multiplied abrasion loss on the metal specimen blocks from three to five times, but also made it impossible to check closely on repeat tests. In the present arrangement the motor is fastened in vertical position to a plate which is bolted to a heavy wooden block, 17, mounted on rubber feet. For additional weight and consequent absorption of vibration, a piece of steel shaft ( 5 cm., 2 inches, in diameter by 25 cm., 10 inches, long) is inserted in a hole drilled in the Fvood block. Thus minor vibration is absorbed by inertia of the heavy block on rubber feet and the method of drive to the first countershaft. The abrasion machine itself is entirely separate from the motor drive and is placed about 20 cm. (8 inches) away from the motor shaft. The machine is also mounted on rubber (typewriter feet, 16), and t,he only connection betxeen the motor and the abrasion machine is the belt drive, which is a light rubber band, 14, cut from a large inner tube. The elasticity and vibration-absorption quality of this rubber helt are a final guarantee that no vibration will reach the abrasion machine. From the top pulley of the first countershaft on the abrasion machine, a sewing-machine belt, 12, drives the second countershaft, vertically mounted, on top of which is fitted the aluminumalloy test pan. All four shaft bearings on the abrasion machine proper are high-grade, ground ball bearings, 15, which also eliminate vibration and reduce friction to a minimum. In designing this machine, consideration was given to the desirability of including a two-direction motion because of the related problems of surface flow on metal specimens and the tendency of particles t o rest in similar positions. Two-direction motion, however, was not added because of the mechanical difficulty of producing it without also introducing lost motion and the consequent bump and pile-drirer effect of the specimen holder at the end of each stroke. TESTPax. The aluminum test pan (Castalloy, 4) is integral with the countershaft on which it is mounted, so that it will run true. In the pan is a recess into \\-hich wax, 5, is poured for the abrasion contact surface. Five brass machine screw permit the pan to be taken off after every test to wash the plate. CUTTITG TOOL. The lathe-tvpe cutting tool, 11, is used to cut the wax to a true flat surface. Before starting a test, the wax surface is planed true and then scraped lightly with a safety-razor blade. After the wax surface has been prepared in this manner, the specimen holders show no up-and-down movement with the machine in operation on an abrasion te.qt.
