A Reciprocating Laboratory Shaker E. R . SCHWV1RZ S ~ LEONiRD D SH4PIROl Textile Laboratory, XIassachusetts Institute of Technology, Cambridge, 3Iass.
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ABORATORY agitating devices map be divided into tn-o main classifications: rotating devices and reciproeating devices. I n rotating devices, the conbainer may be rotated about its own axis, about a line parallel to its axis, or about a line not parallel to the axis of the container-e. g., a line perpendicular to the axis of the container, giving an end-orer-end motion. I n all of these, as the container revolves about a horizontal axis, the liquid surface rives with the container and falls or slides back under the force of gravit'y, producing a tumbling motion. I n rotating devices, t'he speed and radius of rotation are liniit'ed by the fact that when the centrifugal force on the liquid becomes equal to the force of gravity the liquid will remain a t the wall of the cont'ainer and rot'ate with it.
Reciprocating devices impart a much more violent agitation t,o the liquid in the cont'aiiier. The sudden reversals of momentum throw the liquid up the sides of the container, first one way. then the other. A type commonly encountered in chemical laboratories consists of a box with flasks held in place by spring steel strips. The box is driven by a crank and rocker arrangement.
it wa+ desired to ivash samples of cotton in distilled ivater to remove electrolytic salts. Owing to the natural waxes present on untreated cotton fibers, it is exceedingly difficult to wet them out in piire water Ti-ithoiit the acldition of surfaceactive ingredients. Since the addition of such materials Construction of a Reciprocating-T?-pe Agitator might defeat the purpose of the research, it was found necesDuring the course of investigations conducted a t the >I.I. T. sary to design an agitator wvhicli, by purely mechanical means, Textile Laboratory on the electrical conductirity of cotton, would displace the entrapped air iri the cotton and permit wetting out. ; Present address. Interlaken Mill-, Firlierille, R.I. T h e c o m b i n e d i d e a s of -e\reral mernbers of the laboratory staff, together with the genius of a staff mechanic, finally resulted in the conversion of an abandoned c a s t - i r o n base and motor into a very serviceable agitating machine (Figure 1). The machine carries sixteen 300-ml. E r l e n m e y e r flasks which are set into recesses in the carriage and then held firmly in place by a plywood board drilled to accommodate the necks of the flasks. The carriage is thrown rapidly back and forth by a crank-and-lever mechanism giving a quickreturn motion. Wetting-out of the cotton samples was complete in a lcLl few seconds, owing to the yiolence of the agitation, and the washing action was coniplete in less than 15 minutes. SIDE F R O N T The agitator has also been used in special fabric-wash1 FIGURE2. SECTIONAL VIEWS OF MECHANIBV ,
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velocity in the crank, the displacement (from center position), velocity, and acceleration of the carriage have been computed for a complete cycle, using the values: a = 10 cm. (4 inches), b = 10 cm. (4inches), and r = 2.5 em. (1inch). The maximum displacement occurs in this case when the crank has turned only 75" from the zero position (pin at top) The motion of the carriage to the right then takes 210", while the return motion takes 150' (Figure 3). It is interesting to note that, while the slow half-cycle shows uniform acceleration changes, both the positive and negative peak accelerations are crowded into the quick-return half. These sharp acceleration peaks probably account for much of the efficiency of agitation of the mechanism. The quick-return action could be augmented by decreasing the ratio of a to r. Thus, when a = 2r, the maximum displacement occurs a t 60". The two acceleration peaks are then greatly emphasized and occur in the short 120' portion of the cycle. The slow half-cycle takes exactly twice as long (240" rotation). The machine is oiled a t several points to reduce friction losses: crank face and pin, pivot of lever, pin on undercarriage, and the slide supporting the carriage. RECEIVED December 30, 1937.
An Efficient Bottle-Shaking Apparatus GRANT W. SMITH Chemistry Department, University of Kansas City, Kansas City, Mo.
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HE apparatus described in this article was designed for use in an adsorption investigation in m%ich a number
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ing tests. Here, four 2-liter round-bottomed flasks were clamped into place, and the fabrics were placed in the flasks together with the desired amount of water and a number of rubber balls. The balls were thrown back and forth against the fabric, greatly augmenting the mechanical treatment of the goods. Despite the violence of the agitation within the flasks, the machine, after having been bolted firmly to the floor to prevent "walking," ran with surprising ease and quietness. Upon occasions, it has been kept running for 10 hours a t a time, and it has been in use for about 2 years without requiring mechanical attention. DETAILS OF MECHANISM.The crank is driven from the motor through two pulleys giving a six-to-one speed reduction. (A 220-volt 0.1-horsepower motor was run at 110 volts to give an actual crank speed of 160 r. p. m.) The lever is pivoted near its center and is slotted at both ends (Figure 2 ) . One end accommodates the crank pin;while the other end engages a pin attached to the bottom of the sliding carriage. The carriage rests on brass strips movin back and forth in slotted steel strips attached to the base. %he arrangement is fairly evident from the sectional diagrams (Figure 2) and the photograph (Figure 1). Three constants affect the motion of the carriage: r = radius of crank (to center of pin), a = distance from center of crank to pivot, and b = distance from pivot to line of motion of undercarriage pin. Assuming a constant angular
of samples were to be shaken for a considerable length of time. The construction is simple and inexpensive, and the shaker has given excellent service in continuous use over long periods. Although designed originally for use with six 125-ml. Erlenmeyer flasks, i t may easily be adapted to other types and numbers of containers. The device consists essentially of a circular platform mounted at an angle of 15" upon a vertical motor-driven shaft to which it is joined through a ball-bearing joint. Three (or more, if desired) springs attached at the periphery of the platform and anchored to screw hooks in the base prevent the platform from
FIGURE1. EFFICIENT BOTTLE-SHAKING APPARATUS
