AIDS FOR THE ANALYST with fritted glass disks of 10, 30, and 60 mm. in diameter. For practical purposes the medium frit functions well. The fritted tubes also serve t o filter the eluting solutions, but may gradually become clogged; ho-ivever,they can be cleaned with some suitable reagent, as, for instance, nitric acid.
Automatic Cut-Off Valve for Ion Exchange Columns Clifford A. Hewitt, National Bureau of Standards, Washington 25, D. C.
operation of ion exchange or chromatographic columns, IIf thethethelevel bed of the column must always be covered with liquid. of the liquid falls below the top of the bed, the sepaN
ration being made is usually vitiated because of the introduction of air into the bed. Such air in the column bed is difficult to remove and tends to cause channeling. T o maintain the liquid level At above the bed level of the column, many investigators have extended the exit tube to above the bed level of the column. This tube prevents air from being drawn into the bed (1-3). A very simple device, easily constructed, can prevent the level of the liquid from falling below the top of the column bed, and, in so doing, permit the simultaneous operation of many similarly equipped columns without fear of failure. Furthermore, the device permits any definite amount of liquid to enter the column. The device or valve consists of an immersion tube provided xith a frit, the fritted end being immersed in the liquid at LEFT RIGHT the top of the column. The stem of the tube passes through Figure 1. Arrangea rubber stopper which tightly ment of safety valve fits the glass column. I n opL e f t . For analytical work eration the level of the solution R i g h t . For usual ion exchange column above the resin should be about half way between the bottom A . Reservoir B . Rubber stopper of the rubber stopper and that C. Fritted disk of the fritted disk. The flow of D. Resin bed liquid through the disk stops when the level of the liauid added reaches that of the frLtted disk. At this state the level of liquid in the column proper may drop slightly. The fritted disk prevents the liquid in the column from draining because the surface tension of the solution in the pores of the frit is sufficient to prevent air from passing through. Thus a partial vacuum is created above the liquid in the column. When this equals the hydrostatic head, drainage stops. Because it is immersed in the liquid, the disk serves to reduce turbulence when the column is in operation. The disk does not serve to regulate the rate of flow through the column. I n analytical separations, where a definite volume of liquid is known to strip the column of a certain element, the entire volume of the eluting solution can be added a t one time; automatic cutoffs will thus enable the operator to manage a considerable number of columns. Figure 1, left, shoirs the arrangement for an analytical column and right that for the usual ion exchange column where A is the reservoir, B is the rubber stopper, C is the fritted disk, and D is the resin bed. I n the column for analytical separations, it is necessary to use a small frit sealed to the stem of the reservoir tube so that the tube can be inserted through the rubber stopper. A frit of medium porosity would maintain a column of water of about 250 em. in height, and one of fine porosity a column of about 460 cm. The immersion tubes are commercially available
LITERATURE CITED
(1j Sainuelson, Olof, “Ion Exchangers in Analytical Chemistry,” pp. 79-82, Wiley, New York, 1953. (2) Tompkins, E. R., J . Chem. Educ., 26, 92 (1949). ( 3 , Tompkins, E. R., Khym, J. X., and Cohn, IT. E , J . Am. Chen?. Soc., 69, 2769 (1947).
Plastic Dry Box Andrew J. Franklin and Sterling E. Voltz, Houdry Process Carp., Marcus Hook, Pa. SIUPLE
device has been designed for use in procedures which
-4 require the handling of chemicals under “dry box” conditions. -4satisfactory plastic dry box constructed out of readily available materials has been successfully employed in procedures n hich require the transfer of materials under extremely dry conditions, such as the transfer of samples pretreated in a high vacuum system, the preparation of samples for Karl Fischer titrations, and the preparation of infrared samples. .
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I
I/
TOP
OUTLET
VIEW
SIDE VIEW
Figure 1.
CLAMP’
INLET
Plastic dry box
One plastic dry box is illustrated in Figure 1. The most satisfactory plastic materials were those which are sold commercially for use in plastic storm windows. These materials are completely transparent and have a relatively low permeability to water vapor. The plastic was cut to the desired shape and sewed together to form a plastic bag as shown in the figure. The moistureproof seals were then made by pressing a hot flat iron on the edges (including about ‘/a inch on the inside of the stitching) for several seconds. A pair of plastic gloves was constructed out of the same material, sealed in the same fashion, and then sewed and sealed to the plastic bag. The inlet and outlet tubes were prepared by sealing pieces of plastic tubing to the bag in the same manner. After the substances to be transferred were
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