LETTERS Safety Warning: A Modlflcallon of the Methanol Cannon To the Editor:
Useful Papers on Ruchardt's Method To the Edjtor:
We tried the Methanol Cannon Demonstration as described by Summerlin and Ealy ( I ) . We found it to he dramatic and effective. However, after several "firings", one of the nails worked loose in the plastic hottle and became an unexpected part of the demonstration. T o avoid the use of nails and the Tesla coil, we modified the procedure by drilling a hole in the bottom of a 1-L plastic hottle. Into the hole, we inserted the end of a piezo-type gas lighter. After charging the bottle with 1 or 2 mL of methanol and corking the hottle, we struck the lighter. Tying some dental floss to the cork and wrapping the floss around the hottle in a manner analogous to a fishing spinning reel made retrieval of the cork easier.
I wish to draw the attention of your readers to some useful papers on Ruchardt's method for measuring the ratio of heat capacities of gases, additional to those reported in our recent Daoer ( 1 ) . kn e k e r description of methods that use harmonic motion (both Rhchardt's method and Kundt's tuhe) was vubfished in this Journal by J. A. Schufle [1957, 34, 781801. Direct observation was used for the data collection. Two recent papers (2,s) use electronic data collection methodsthe latter DaDer (.?I was published simultaneousl~with ours! These report on the deGelopment by Hunt of the use of an unluhricated 50-mL syringe and plunger as gas-containing vessel and piston, together with an accelerometer to detect the plunger's oscillation after i t is momentarily depressed; the accelerometer substitutes for the pressure transducer that is in our equipment. The volume of gas used is considerahlv less than in our svstem. Data on the oscillakons is collected electronically but is not suhiected to the more c o m ~ l e t eanalvsis that we recommend.
Llterature Clted 1. Ckemied Dpmonsfrofians, 2nd ed.; ACS: Washington, DC: 1988: pp
256.
Mark Alber John Chambers Georgetown Preparatoty School Rockville, MD 20852
Llteralure Clted
Llesegang Rlngs Uslng Sodlum Slllcate To the Editor:
1. Orehsrd, 8. W.; Giasaer. L. J Cham. Educ. 1988.65.824-826. 2. Huot. J. L. Amer. J. Phya. 1985,53,696697. 3. Bligh, P. H.:Higp,D.;V~r,B.P.Phys.Educ. 1988,23,31&316
Schibeci and Carlsen, in their article on Liesegang rings [J. Chem. Educ. 1988,65,365], mentioned that they had no success with sodium silicate solution. I recently did some undergraduate independent study work involving Liesegang rings, and I would like to point out two very successful results that I obtained usine sodium silicate. The desired sodium silicaie solution has a density of 1.06 e/mL and can be ~ r e ~ a r bv e dmixine 1360 m L of water with 1250 mL of comm&&l wateiglass (iensity 1.385 g/mL). Rinas of basic CoDDer chromate (CuCrOa.Cu0.2H20) can be forked as follov&(l): add sodium silicate solution to an equal volume of a solution that is 0.5 M in K,Cr04 and 0.5 M i;acetic acid in an 18 X 150-mm or 25- X 200-mm test tube; mix the solutions by inverting the test tuhe, andallow thegel to set. Gelline reauires ahout 10-20 min. hut the best results are obtained if the gel is allowed to set for a few hours or overnieht. Add 0.25 M CuSO, to the eel in the test tuhe and d o w iiffusion t o occur. Rines of "banded malachite" lhasic comer carbonate. CUCO.~.CU(OHJ~] ran he formed as f o l l o w s ~add ~ ~ :sodium silicate solution to an equal volume ot'a solution that is 0.25 M in (NHa)2C03in an i8- X 150-mm or 25- X 200-mm test tube; mix by inverting the test tuhe and allow to stand overnight. Add 0.25 M Cu(N0d2 or 0.25 M CuClz as the diffusing reagent. If the diffusing solution is replaced with freshsolution eachday for the first five days,very nice hands form. In addition to these two comer s are .. ~. r e c.i ~ i t a t ethere many other compounds that will produce Liesegang rings in sodium silicate eels The first reference below IS an excellent source for possible experiments involving precipitates in silicic acid gel&
.~ .
Literature cite& 1. Holmes.Herry N. J $hw 2. Kanning, E. W.;K
Chom 1917,21,709
k G.i.; ~ k m s nR. , J. J. &em Educ. 193411.346.
Jonathan E. Forman Calltwnia State University San Bernadine San B%mardino, CA 92407
720
Journal of Chemical Education
University of the Witwatersrand P.O. Wits
2050 SOU% Africa
Plcturlng Alomlc Magnitudes To the Editor:
I agree with Thomas Lehman (1988,65,282) that teachers should try t o make atomic magnitudes as conceivable as possihle (Educ. Chem. 1983,20,81 (see answer to question 4 in col 1)). Some illustrations that do this are the followins: (1) A speck of iron 0.01 mm X 0.01 mm X 0.01 mm is j;st visible to the naked eye. Along one edge of such a speck there are about 40,000 atoms. This corresponds to the number of spectators in a large sports crowd, and can just about be visualized. (2) A cube of iron containing one mole of atoms has sides of about 2 cm. Along each edge there are about 80 million atoms. This is not a visualizable number hut falls within the range used in everyday life. T o obtain such a number, one can subdivide the 2 cm with the help of a ruler: in 1mm there are 4 million atoms, in 0.1 mm there are 400,000, and in 0.01 mm, which one can just about gauge on a ruler, 40,000. (3) Ordinary gold leaf is about 0.0001 mm thick (Partington, J. R. General and Inorganic Chemistry, 2nd ed.; Macmillan: London, 1954; p 354). This corresponds to about 400 atoms. Although the thickness of gold leaf cannot he gauged with the eye, a feel for i t can be obtained by handling the material. Even thinner films of gold can he obtained on supporting surfaces, but the thickness of these is more difficult to visualize. P. G. Nelson University of Hull Hull HUB 7RX England
