All-Glass Ball Valve Stirrer SILVESTER LIOTTA City College, College of t h e City of New- York,
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DAMS ( 1 ) describes a special met'al stirrer which promotes equilibrium between solid and liquid phases by lifting the solution from the bottom of the Dewar container and allowing it to flow down over the ice and thus percolate to the bottom of the container, where the cycle is repeated. This type of stirring possesses the advantage of producing positive circulation, and, since the stirrer operates a t speeds as low as 10 strokes per minut'e, of eliminating danger of heating due to friction. The stirrer described by Adams is made of brass protected by gold plating. However, other workers h a r e found that such gold plating provides inadequate protection against corrosion by certain solutions, possibly because of undermining of the gold plate or wear and exposure of the brass. To meet this problem, glass was chosen since it is unreactive t'o a large number of reagents, and the stirrer was designed as follows:
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shape at the point of grinding, no harm is done, since the extra weight at this point will keep it down and out of contact with the valve seat on the piston. On the other hand, should the ground portion become lighter than the remainder of the bulb, the same purpose viill be accomplished, since the point xi11 then remain on top where no contact is made. The valve 5:eat may be ground with a spherical or conical surface, if necessary, in order t o reduce lrakage to a minimum.
It is satisfactory to have the diameter of the ball equal to three fourths of the inside diameter of tEie pibton, and the hole serving as the valve seat equal to half the inside diameter. Two or three inward projections. F , should be made
I n Figure 1, A represents a glass cylinder which is equipped with a grill, B , made by fusing 0.0625-inch glass rods 0.0625 inch apart. The bottom view of this grill is shown in C. Within this cylinder is the moving piston, D, which is cylindrical in form, with turned-in end to support the glass ball valve, E. Piston D should be of such diameter that it just slides freely within cylinder A without danger of binding. The success of the stirrer depends on the ball valve, E. Its weight should be adjusted so that it just sinks in the liquid which is to be stirred. The maximum efficiency is obtained when this adjustment is close. However, practice has shown that the adjustment is not too critical with increasing tolerance as the stirring speed increases. The stirrers constructed in connection with the author's apparatus worked satisfactorily a t speeds as low as 5 strokes per minute. The best method of constructing the holloK ball, E, is to accumulate some extra glass on one side, making the ball too heavy, and then t o grind off portions until the weight is adjusted. Should this procedure leave the ball distorted from a spherical
FIGURE2 .
~ 0 M P I . E T E DSTIRRER
in cylinder A, in order to prevent the piston from touching and damaging the grill. The grill may be omitted if the solution used does not contain ice or other solid matter. Adams' stirrer was semicylindrical in form and was seated in the Dewar flask by means of a spring. Sirice this cannot be done with glass, the diameter of the cylinder was made approximately two thirds of the diameter of the Dewar flask and was kept in place by nieans of three projecting glass rods sealed to the top (a. b, c) and one to the bottom, d. The dotted line indicates the malls of the Dewar flask against which contact is made. The weight of the cylinder is sufficient to keep it in place. A photograph of the parts of the stirrer is shown in Figure 2. This type of glass stirrer is suitable for use in any type of solution, corrosive or otherwise, which requires a slow-motion type of stirring, with a positive flow from bottom to top.
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Acknowledgment iicknouledgment is made to the Associated Experimental Laboratories of Brooklyn, S . Y., for permission to describe this stirrer.
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Literature Cited
FIGURE1. CONSTRUCTIONAL DETAILS OF STIRRER (left) AND METHODOF SEATINGSTIRRERIN DEWARCONTAINER (right) 173
(1) Adams, L. H.,J. Am. Chem. SOC.,37, 481 (1 915).
