.dit.d by:
WALTER A. WOLF Colgots Unvsrsty Hornillon. New York
Laboratory Work in a Nonlaboratory Course Thomas McCullough, CSC St. Edward's Uniuersity Austin, Texas 78704 For one reason or another some college chemistry courses do not have an accompanying laboratory section. As a compromise hetween a full laboratory program in a given course and na lab a t all, ouy Department offers to interested students the opportunity to carry out long range experiments which require very simple equipment and a minimum of time expenditure. In most instances the student will titrate a solution, carry out several spot tests, run a brief chromatogram, or simply observe a reaction: operations that would be performed once a week and in just a few minutes. The major difference between the topics in this paper and ordinary experiments is time. In the case a t hand we desire slow reactions and slaw changes. We don't want to deal with phenomena that can be evaluated in a few hours, or even days. A very practical goal is the determination of the shelf (or lab) life of commonly used analytical solutions. What effect will air or light have an them? How long can inhibitors prevent air oxidation of certain labile compounds? What effect will the rate of formation have an the shape, size, and melting point of crystals? How long will a spotted paper or thin layer chromatogram retain its ability to he developed and detected? The list can he extended almost indefinitely. A final consideration is the laboratory space required for these semester-long projects. In small schools which have laboratories "lying fallow" one or more days per week, there is no problem a t all in finding an unused drawer or locker and other needed facilities. In Larger schools, however, this may not he true, so the interested student will have to choose a n experiment which can he kept in a box and followed a t home.
A New Gravimetric ~ x ~ e r i m e nfor t General Chemistry Don W. Havden ~aliforniaState College, Stanislaus Turlock, California 95380 The two gravimetric experiments most commonly done in Quantitative Analysis are probably the determination of sulfate as barium sulfate and the determination of chloride as silver chloride. Both of these experiments have been adapted to general chemistry courses, but the filtration of barium suliate is tedious and the results are frequently inaccurate due to improper burning of the filter paper. The results of the chloride experiment are more consistent, but the cost of silver nitrate must be considered and the gravimetric chloride experiment is frequently reserved for the quantitative analysis course. The determination of magnesium as magnesium oxalate is rarely done as an undergraduate experiment, but axalate ion can be generated hamogenously by hydrolysis of urea in an oxalic seid-ammonium oxalate solution using a simple procedure which requires only inexpensive and relatively nan-toxic chemicals. The crystals of MgCz04.2H20 are easily filtered through sintered glass crucibles, and can he dried and weighed in 1 hr. A single sample can be analyzed in one 3-hr laboratory period and gives results that average accurate to within 2%. Detailed instructions are available from the author onrequest.
On Demonstrating Line Spectra W. H. Slabaugh Oregon State Uniuersit3 Coruallis, Oregon 97331 We agree with Driscoll! that projected spectra of excited gases such as hydrogen are too weak for classroom purposes. After exploring this problem for some time we arrived a t an inexpensive yet effective method of displaying spectra which is given here. Ordinary gas emission tubes, such as those commonly available for hydrogen, neon, mercury, and such are placed on the lecture table. Between the tube and the students we place a semicirculady mounted diffraction grating (13,400 grooves per inch, Catalog No. 50,180 a t $5.95 from Edmund Scientific Ca., Barrington, N.J. 08007). The grating material which comes in a 6-ft roll was sectioned into l-ft lengths and mounted with the grooves in a vertical position. The plastic grating is held between two sheets of in. Plexiglas, curved and screwed to a semicircular piece of plywood along with suitable framing to hold the mounted grating in rigid, curved farm.
In a fully darkened room, up to four distinct lines of the hydrogen spectrum are visible t o all students. Brighter spectra, such as that of neon, are even more intense. The gas tube should ideally be constructed with as narrow constricted zone as possible because there is no slit, other than the light source, involved in this arrangement. We have succeeded in introducing Planck's black body radiator concept with this device. A piece of Nichrome wire mounted ver. tically and attached to a variable voltage source is placed behind the semicircular eratine. Gradual heatine of the wire oroduces a red soectral reeiai which exnands into the oranee. ereen. .. . veliow. , hlue and violet iertions as higher voltages are applied to the wire. Qualitatively, one may nare lnrrea~lngintensitw* of spectral re. gmnr as a iunction of mcreasine frequencies ofem~ttedradiation
' Driscoll, Jerry A,, J. CHEM. EDUC., 51,97 (1974). Editor's Note: This column is devoted t o hrief announcements of new ideas in chemical education. These consist of succinct statements of the key ideas of the authors along with possible information on obtaining further material related to the subject upon request. Authors who wish to submit articles far consideration fa? ~uhlicatianshould send the manuscripts (one double-spaced; typewritten page) and the supporting materials to Dr. Walter A. Wolf, Editor, Chem Ed Comnaets. D e ~ s r t m e n tof Chemistw. .. Caleate - University, ~ a m ' i l t o n , ' ~ eYork & 13346.
Volume 51, Number 72, December 1974
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