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WALTER A. WOLF Colgde Uniwnily Hemllton. New Yodl
A Good lnexpensive Table for Analytical Balances Charles G. Moseley The Ohio State Uniuersity-Lima Campus Lima, Ohio 45804 Our school recently faced the problem of providing good tables for analytical balances used by our first-year chemistry students. A limited equipment budget and the high cost of commercial balance tables ($200-250 each) precluded their acquisition. Investigation showed that excellent balance tahles can be constructed very inexpensively from readily available concrete products. Each table consists of a top working surface (2 ft X 3 ft X %in. precast concrete slab) supported by two pedestals (each of four 8 X 8 X 16-in. concrete blocks). All material was given one prime coat and one top coat of water base paint to improve appearance. The balance operator sits on a 18lh-in. high stool. As shown below, the tables compare favorably to commercial balance tables1. Commercial Marble
Commercial Concrete
Our Concrete
31X35X24 750 lbr. $238
31X36X24 650 lbs; 400 IDS. 8224: 8191
32VrX36X24 510 lbs.
Dimensions (in.)
IhXwXd)
we~gnt Cost
$11.50
If required, the weight of the tables could be increased by simply filling the boles in the concrete blocks with concrete, sand, or other massive material; however, this was not found to be necessary for satisfactory balance performance. In addition, balance performance is also satisfactory on a row of tables constructed of the same material hut using shared internal pedestals (i.e., each internal stack of four blocks supporting ends of two slab tops). Cost and labor (but also weight) are obviously even lower for this shared pedestal type of table. 'This data
was
taken from the 1976 edition of tke Scientific
A polyethylene washing bottle is fitted with a one-hole ~. . rubber stopper through which u pipet has heen inserted. The tipof the pipet .should reach nearly ro the bottom ofthe bottle. When the liquid is being stored, the open end of the pipct is rovered with a ruhber l ~ u l bfrom a medicine dropper. Durinp. operation, the medicine dropper bulb is remo;ed, and the bottle is squeezed until the liquid rises above the mark on the pipet. The open end of the pipet is covered with the finger of one hand, while the rubber stopper is loosened from the bottle with the other hand in order to equalize the air pressure. The liquid in the pipet is drained to the top mark while the pipet tip is still within the bottle. The filled pipet is then ready for use in the usual manner. The rubber stopper remains attached to the pipet during the entire pipetting operation.
Skits for General Chemistry Rnbin Battino Wright State University Dayton, Ohio 45431 We have prepared skits on a variety of subjects, which we are using in general chemistry courses as a change of pace from lecturing. The skits are best performed by the lecturer and teaching assistants since it takes some skill to act and project them to a large audience. Students are told that hissing, booing, laughing and other reactions are appropriate-since this is a change of pace many students need permission to react. Many of the skits are deliberately "corny" and "hammy," but also contain didactic content. They are nrostly meant for fun. The titles of the ones we have prepared are: "The Student-Teacher Contract"; "It's a Gas, Man"; "Simply Pure Damn Foolishness"; "Corn is an sp2 Hybrid"; "How Can You Balance an Equation?"; But, is it like Relevant, Man?-A Morning Farrago"; and "Thermogoddammits." Upon request we will be pleased to send you a package containing all of these skits. You are free to use them as you wish. (To cover the cost of reproduction, handling, and mailing, a contribution of $1.00 would be appreciated.)
Products Catalogue.
An lnexpensive Safety Pipet for Reagents Thomas Rees Phillips Academy Andover, Massachusetts 01810 Various designs of rubber bulbs are used for pipetting liquids safely. We have designed a simple, safe device which is more convenient and less expensive than the rubber bulb. This device can be used with all liquids that are compatible with the container. 502 / Journal of Chemical Education
Permanent Models for Determining Absolute Configurations Charles J. Thoman, S.J. University of Scranton Scranton, Penmyluania 18510 The study of stereochemistry today is not complete without instruction in the use of the Cahn-Ingold-Prelog procedure for expressing absolute configurations. Typically, the instructor will draw a Fischer projection formula on the board
(or employ one from the textbook), use a model of some sort to show the three-dimensional meaning of it, and then apply the Cahn-Ingold-Prelog priority rulesio either the drawing or the model. For the final step, however, he or she will almost invariably use the model to determine the R or S designation, since it is easier to manipulate into the necessary position (with the group of lowest priority behind the c h i d atom) than the hlackboard or even the textbook. This works very well as a pedagogic approach. Students may even be urged to buy models and allowed t o usethem in suhseauent examinations. This. however. can hreed an unhealthv debendence on such models, so that without them some may find themselves incapable of handling any but the simplest prol)lcms. The alternative to carrying models wirh you twenty-four hoursaday is to have and beable to use huilt-in models that are always available when needed. Such models are at our constant disposal: our hands. T h e purpme ot'this report is to describe briefly how the hands may he used to determine K and S configurations. It is assumed that the fundamentals of the Cahn-lngold-Prelog method are known.
1) The wrist always represents the group of lowest priority; the thumb, index and middle fingers, the other three groups. The remaining two fingers are folded into the palm. 2) Fischer projection formulasare m a t often written with the main carbon chain extending vertically. If the group of lowest priority is to the left, the left hand is used; if to the right, the right. In either case, the first three fingers are positioned to accurately represent in space the other three groups. 3) The priorities of the other groups are then "assigned" ta the proper fingers. 4) The hand is then turnedtoward the face, with the wrist (i.e., the group of lowest priority) on the opposite side. The other groups (fingers)are now fanned out in perfect view, and the progression from highest to lowest priority can he seen to he either clackwise and R or counterclockwiseand S.
This system can be adapted readily to more complex examples like the chair form of cvclohexanes. Classroom experience has shown that i t is easily grasped and, once learned, is remembered and available as a tool far into the future.
Volume 53.Number 8, August 1976 / 503
