In the Laboratory
edited by
Cost-Effective Teacher Harold H. Harris
University of Missouri St. Louis
St. Louis, MO 63121
Low-Cost  Vacuum Desiccator
Frederick Sweet
Department of Obstetrics and Gynecology, Washington University School of Medicine, Saint Louis, MO 63110;
[e-mail]
For over a century, solids and liquids that had to be kept plastic bags of various sizes. Two 11 in. × 120 in. rolls of the
dry were stored in glass desiccators containing a drying agent thick shrink-wrapping material (also distributed by Rival)
such as anhydrous calcium sulfate. Today, the need for stor- costs less than $10 per box and the two rolls can be used in a
ing a variety of air- and water-sensitive chemicals under dry laboratory for making from 30 to 60 desiccators.
conditions is still a common practice in undergraduate, gradu- Conventional glass desiccators require careful greasing
ate, and research chemistry laboratories. Yet the commercial at the ground-glass interfaces to achieve a perfect seal. Plas-
glass and plastic desiccators have become more expensive.1 tic desiccators are known to eventually leak because over time
Moreover, they chip, crack, and break with regularity in un- the plastic interface tends to warp. But once heat-sealed, the
dergraduate chemistry laboratories. Vacuum desiccators are disposable desiccator bags (Figure 1B D) remain completely
even more expensive than the simple two-piece variety. intact until they are cut open. Each 11 in. × 120 in. roll of
During the past eight decades, a number of inexpensive this material can be used to make approximately 30 small (4
desiccators (1 3) have been reported, some made from a va- in. × 11 in.) disposable desiccator bags for about $0.17 each
riety of novel materials such as: plastic sandwich bags (4), or 15 large desiccator bags (8 in. × 11 in.) for $0.34 each.
coffee cans (5), and cookie jars (6). The present article de- After the contents are heat sealed together with a desiccant
scribes how a new kitchen appliance costing less than half they remain dry indefinitely. Moreover, the shrink-wrapped
the price of a single, large desiccator1 can be used in the labo- item and desiccant do not take up more space than the origi-
ratory for quickly producing low-cost, disposable  vacuum nal items as opposed to the space occupied by a conventional,
desiccators . The appliance, which has a small foot print (6 glass desiccator.
in. × 15 in.) is marketed for quickly, conveniently, and inex- An oversized heat-sealed desiccator bag can be used sev-
pensively shrink-wrapping foods for storage in a refrigerator eral times by narrowly cutting it open in a straight line along
or freezer. But the same device can provide an entire under- the seal after its first use. The open side must be trimmed in
graduate chemistry laboratory with easy-to-use and dispos- a straight line so that the bag can be quickly resealed in the
able desiccator bags for a small fraction of the cost of Seal-a-Meal device.
conventional glass or plastic desiccators. In addition to serving as an unbreakable and inexpen-
In the present example, the Seal-a-Meal device (Figure sive desiccator, the system is useful for sealing bottles and
1A) distributed by the Rival Company of the Holmes Group, vials of corrosive and irritating substances and also large
Inc. had been purchased by the author for less than $100 at bottles of solvent that do not fit into a large desiccator (Fig-
a neighborhood K-Mart store. This appliance came with two ure 1D). Unlike Saran Wrap or similar cling film, once the
rolls of a double-walled, heavy-plastic material measuring 11 double-walled, heavy-plastic material is vacuum-sealed it is
in. × 120 in. (Figure 1E); plus an assortment of specialized indefinitely impermeable to vapors. Thus six months after
Figure 1. Adapting an automated kitchen gadget for making
 vacuum desiccators :
(A) The Seal-a-Meal device can be used for heat sealing with
or without a vacuum. A 120-inch roll of double-walled,
heavy-plastic material is located under the shrink-wrapping
section of the appliance that contains a horizontal cutting
device.
(B) A reagent bottle with Drierite in position for shrink wrap-
ping. The entire automated shrink-wrapping process takes
about 15 30 seconds, depending on the size of the bag.
(C) A bottle of isobutyl chloroformate (100 g).
(D) A 1-L bottle of dioxane that had been sealed with the kitchen
gadget.
(E) Extra roll of 120-inch double-walled, heavy-plastic material.
1500 Journal of Chemical Education " Vol. 81 No. 10 October 2004 " www.JCE.DivCHED.org
In the Laboratory
having been shrink wrapped, several grams of moisture indi- 280 mm Nalgene desiccators; $234 for 140 mm and $494 for
cating Drierite (behind D in Figure 1) remained completely 190 mm vacuum desiccators (Fisher Scientific Company Cata-
unchanged. Similarly, no HCl was detected inside the desic- log 2003).
cator after a shrink-wrapped bottle of isobutyl chloroformate
(Figure 1C), which forms HCl on contact with moisture, had
Literature Cited
been standing in a laboratory for five months.
The author has not yet sealed materials under an inert 1. Day, J. E.; Walke, E. W. J. Chem. Educ. 1928, 5, 597.
atmosphere such as nitrogen or argon. However, this can eas-
2. Birdwhistell, R. K. J. Chem. Educ. 1967, 44, 667.
ily be done by flushing the air out of a bag with a stream of
3. Hendrixson, R. R.; Whitcomb, D. R.; Palmer, R. A. J. Chem
inert gas immediately before vacuum sealing it.
Educ. 1976, 53, 593.
4. Thompson, H. B. J. Chem Educ. 1966, 43, 473.
Note
5. Minnier, C.; Johnson, S.; Matusz, I. J. Chem Educ. 1976, 53,
520.
1. The costs for desiccators are: $65 for 100 mm and $181
for 250 mm glass desiccators; $67 for 230 mm and $96 for 6. Sarma, B. D. J. Chem Educ. 1983, 60, 906 907.
www.JCE.DivCHED.org " Vol. 81 No. 10 October 2004 " Journal of Chemical Education 1501