and Jonathan Turk
The City College of the City University of New York N e w York, N.Y. 10031
Diffusion-Seal Desiccator for Student Use
A
recent patent' describes an inexpensive student desiccator that dispenses with the usual hermetic seal between the dry inside space and the ambient outside air. Instead, the desiccant bed itself provides the seal. Before moist outside air can enter the inside space, it must diffuse through a layer of desiccant. Figure 1shows the assembled apparatus, which consists of a lower member, having a circular trough to hold the desiccant, and an upper member that is an inverted cylindrical dish whose rim is partly inserted into the desiccant. Figure 2 shows the apparatus disassembled, with a crystallizing dish containing material to be dried.
Figure 1.
Diffusion-sea1 deliccator.
Fioure 2.
(CaSOr desiccant with a cobalt (11) indicator), under the conditions of testing described above, showed that while the outside desiccant turned pink (wet) the inside desiccant was still relatively dry, as evidenced by its blue (at 47y0 R.H.) or purple color (at 64% R.H.) at the end of one week. The results indicate that the diffusion-seal desiccator is effective for student use for drying times up to one week (the usual interval between laboratory periods), even under conditions of high ambient humidity. No liquefaction occurred in the outside desiccant under the conditions of the tests: the inside desiccant remained
Desiccator diaonembled.
Figure 3 is a cross section showing the arrangement of desiccant and upper and lower members of the apparatus. The design provides economy (cost is a fraction of a conventional student desiccator), saving of space (members can he nested), and multiple use (the upper member also serves as a plastic beaker). The apparatus was tested, using anhydrous CaCll as the desiccant, in an atmosphere of controlled humidity within a plastic bag. The saturation of the "inside" (nonexposed) and of the "outside" (exposed) desiccant was measured by withdrawing separate samples from a series of replicate desiccators and heating them to constant weight over a Bunsen flame. Figure 4 shows the progress of saturation of the two portions of desiccant a t 47% relative humidity and 27'C. A series of tests a t 64% R.H. and 27'C showed the same relative patterns of saturation; the ouside desiccant reached the stage equivalent to the dihydrate within 3 days whereas the inside reached the monohydrate stage in a week. Observation of color changes in indicating "Drierite" 'TURK,A,, US. Patent 3,288,566 (Nov. 29, 1966). The apparatus is manuisctured by Bel-Art Products, Pequsnnock, N. J. 07440, and is distributed through laboratory supply dealers.
Figure 3.
Dericcotor crorr-ledion
granular and free-flowing. The apparatus should therefore be useful in laboratories of general and organic chemistry, where considerations of space and cost have heretofore precluded the routine distribution of desiccators.
Tlme Figure 4.
S a h l r d i o n of dosiccant at 27
Idoys)
2' C and 47 X 2% R.H.
Volume 44, Number 7, July 1967
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