ANALYTICAL EDITION
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require from 20 to 30 minutes for slotting. Finally, the glass niust be held in a firm and fixed manner while grinding so that no undue strain is exerted on that portion of the slot already formed. When properly performed, the above process produces a neat clean-cut slot free from any sign of chipping, These slotted watch glasses have been used frequently by the author and by students in this laboratory and have proved very satisfactory for covering beakers during elec-
Vol. 4, No. 2
trolytic determinations. Undoubtedly similar ones or suitable variations of them might well find application in other situations where it is desirable to provide a cover glass that may be readily removed and replaced in spite of obstructions that would otherwise interfere The writer wishes to acknowledge his indebtedness to E. W. Wilson, glassblower at the Frick Chemical Laboratory, for supplying the practical details of the above method. R E C E I V ~November D 30, 1931.
Multiple-Range Flowmeters SAMUEL YUSTER,University of Minnesota, Minneapolis, Minn.
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N THE study of gaseous reactions by flow methods, it is often advantageous to have a multiple-range flowmeter because of the necessity of a wide range in rates of flow in the problem. I n many cases the range is varied by inserting capillaries of different size by means of rubber tubing, but rubber has the disadvantage of aging and leaking, and corrosive gases attack it. During the course of some work on halogenation, the flowmeters described in this article were designed and found to work very satisfactorily. Their ranges are changed simply by turning the stopcocks. I n Figure 1 the gas passes in at A and through capillary D or E, according to the range desired, and out again at B. By turning stopcock C through an angle of 180 degrees, the two capillaries are alternately placed in the line. After sealing the flowmeter into the line, the manometer limbs are
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degrees, closing off both D and E, and the new range may then be adjusted. If a three-way stopcock is not available, the capillaries may be sealed on in parallel, using one ordinary two-way stopcock for each. I n Figure 2 the gas passes in at A and up into C, which is joined to the rest of the flowmeter by a ground-glass joint. The gas then goes down the capillary which is in mesh with B and out to the rest of the line. C is held to the rest of the apparatus by means of wire or small springs and the arms M , 0, and P.
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I
FIGURE 1
FIGURE 2
filled through stopcock F. If too much manometer liquid is allowed to flow in, or if it is necessary to change the liquid, it may be removed through stopcock G. H and Z are constrictions which smooth out any pulsations in flow due to the passage of the gas through a wash liquid. The bulb J prevents the manometer liquid from being blown into the line because of a sudden rush of gas. The liquid is merely blown into the bulb and when conditions are normal again, it drains back into the limbs of the manometer. If more than two ranges are desired, another ensemble of a three-way stopcock and two capillaries may be sealed on a t A and B. Stopcock C is then turned through an angle of 90
To change the range of this flowmeter, C is rotated through such an angle as to bring the proper capillary in mesh with B. Although only the two capillaries D and E are shown in the drawing, three or four may be sealed on, giving as many ranges I n filling the manometer arms, C is removed and the liquid introduced. ACENOWLEDGMENT The writer wishes to acknowledge the helpful suggestions of A. Cameron in the design of these flowmeters. R B C E I V ~January D 4, 1932
