Bolllng Tube Precautions
letters Hydrogen Halldep To the Editor:: My previous paper [J. CHEM. EDUC., 53,17 (1976)l made four main points. The first was that free energy changes are needed as a basis for discussing equilibria, rather than enthalpy. The second was that hydrogen halide molecules are virtually certain to form hydrogen bonds with water. I have written a paper containing much more corroborative evidence, which I will publish elsewhere. Only brief evidence can be given in the limited space here. Water forms hydrogen bonds with itself, with a strength (AH) of about 5-6 kcal/mole, both in vapor and liquid. H X bonds with ethers (about the same polarity and structure as water). For H F the AH is 8-10, for HC1 and HBr i t is about 6 7 ; both gaseous and liquid. There is no direct evidence, but data for IHI-, BrHBr-, and CIHCI- indicate for HI about the same strength with ethers as for HCI and HBr (and, by analogy, with water). Therefore the bond strength between water and HX will be as strong as, or stronger than, that between water itself. Dr. Pauling insist$ that ". . . the differences in the electronegativity of the heavier halogens and hydrogen is far less than the The electric mo~~~-difference for fluorine and hvdroeen. . ments are far less, and the ability to form hydrogen bonds is far less." The data for ethers land other hiehlv- -~ o l a moler cules) contradict this. The afdrementioned article contains an explanatory hypothesis. The third point was that H X molecules would therefore dissolve in water with a rather lame neeative AGO. The fourth wm the as yet unproven suggestion tha;, by analogy with other hvdroeen -hond- formine substances, all HX would dissolve w;th &out the same val;e of AGO. ~~~
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To The Editor: The appearance of my note describing the construction and use of a simple ebullition tube [this Jourwl, 53.50 (1976)] has prompted Dr. B. J. Luberoff to raise certain questions concernine the reo oar at ion and handline of the tubes. In the event ;hat inexperienced laboratory personnel (e.g., undergraduate students) are involved in making and in subsequent use of the tubes the following points may be explicitly noted. (1) The Pyrex tubing that is fused to the rod may be significantly longer than the 10- to 15-mm length quoted in the Note, then cut to the shorter lendh after the tube is annealed. In this manner i t is unnecessarysaryto hold the short piece of tubing in a mechanical device during the fusion. (2) Both ends of the completed rod should be fire-polished to avoid scratching the inside surface of the boiling flask. (3) If the temperature of a solvent or solution drops much below the b o i point for any reason the liquid will rise rapidly into the open end of the boiling tube, displacing d of the remaining air that is essential for the tube's function. (If this occurs not only does the tube become inoperative but it also becomes a menace since the flask's contents may then bump and turn the boiling tube into a ~roiectilethat mav ruDture the flask with disastrous consequdnces.) The flask m;st be allowed to cool well below the boiline ~ o i nand t the liquid in the tubeshaken out in order to reestarbfish an air source; The liquid may then be brought back to boiling. We have employed boiling tubes in our undergraduate laboratories for many years with no problems. The most important point to impress upon a student is to introduce the tube carefully into the boiling flask-it is possible to drop it through the bottom of the flask. When prepared and handled with the precautions given, I feel that the boiling tube is the most satisfactory device available to control the boiling of liquids a t atmmpheric pressure.
A. T. Rowland Gettysburg College Gettysburg, Pennsylvania 17325
R. Thomas Myers Kent State University Kent. Ohio 44242 *Editor's Note: Written in response to the paper by Pauling on p. 762 ofthis issue.
Open Laboratories To the Editor: The article by Hamilton and McMahon, "An Open Laboratory Approach for the Community College," [J. CHEM. EDUC., 53,246 (1976)] prompts the following comments. The authors are not alone in their mixingof students from different courses in the same open laboratory. Since 1971, we have mixed general chemistry students during the first semester with sophomores taking quantitative analysis and during the second semester with organic students. We are usine a 24-station laboratorv which is open to students aDproximately 30 hrlwk. video tapes of necessary labor at^;^ techniques are viewed by general chemistry students in the librarybrior to an experiment.. We are constantly aware of the potential dangers cited hy the authors in mixing organic students with others although in the past five years we have not experienced any serious accidents attributable to the mixing.
Etymology of Chemistry To the Editor: The letter by James J. Glackin [J. Chem. Educ., 53, 267 (1976)] raises the question of whether the ultimate origin of the word "chemistry" is the Egyptian work "Khem" which meant black and was also the name for Egypt. It seems certain that the modern terms "chemistry" and "alebemy" derive from the Arabic a1 kimia. The Arabic term, however, is more likely to have come from the Greek chemia or chymio for chemical work, than directly from the Egyptian km or kmt (Egyptian does not indicate vowels) or from the Chinesejin-yi, meaning gold juice. The origin of the Greek is controversial, hut it nrobablv came from the Greek metallureical term chyma, ingot. The derivation was influenced by the Egyptian km as well as bv the Greek chvmos and rhvlos. ~ l a n iuire. t After a twentyItwo page disc;ssion of these matters,-~ack Lindsay' concludes that this, . . seems as far as we can go in unravelling this difficult etymological knot.. .".
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' Undsay,d.. "Theoriginsol Aiehcrny?Frderick 4, pp. 6-9.
Muller. Ltd.. London, I910. Chapter The historians of eherniatry have, indeed. "a word or two to say about
this."
R. F. Trimble University of Wisconsin Center Wset Bend, Wisconsin 53095 802 / J m l of Chemical Education
Joseph M. Diamanti
Southern Illinois University Carbandale, Illinois 62901
