letters Determining Chirality To the Editor: Richardson's "Algorithmic Method for the Recognition of Theoretically Chiral Octahedral Complexes" [J. Chem. Edue. 51 347 (1974)l reauires a listine of the "trans pairs" and is therefore es~ent~ally a restatement of the i3ailar svmhol IBailar, J. C.. Jr., J. Chem. Educ., 34, 334 (1957)l. - ~ a y i e rshowed [J, dhem. Educ., 34, 623 (1957)l that simnle interchanees on Bailar symbols can establish their chiiality or achi&ity; if chiral (hey can be converted into an eauivalent confieuration only hy an even number of interchanges, if achirLl by any number. The criterion is similar to Richardson's, except that his breaks down when applied to bidentate ligands that are not symmetrical. Symbolizing the two ends of the ligand by A and B, and marking a second such ligand with primes, we have types such as: I :AA' n : AB' BB' cd
BA'
cd In applying Richardson's conditions, a pair AB must be regarded as "identical" to BA. Because of the placement of primes, neither of these types contains "identical" pairs or a pair with identical members, and both would then meet the conditions for chirality. Nevertheless, Type I is chiral and Type I1 achiral. Three interchanges on Type 11: AB' BA' cd
- - AB' A'B cd
A'B AB'
A'B . B'A
ed cd together with a reassignment of primes, will yield the original, but Type I will always require an even number of interchanges. This criterion can he applied to complexes with tridentate or even hexadenate ligands. An EDTA complex, for example, symbolized NO' is clearly chiral. 00' ON' S t u a r t A. M a.s.~ e r University of Bridgeport Bridgeport, Connecticut 06602
Stability of Silicon Monoxide To The Editor: An error in the article entitled Speciality chemicals by John Haschke [J. Chem. Educ., 52, 157 (1975)] should be corrected. Silicon monoxide solid is not only preparable in the laboratory, but it is available commercially in ton lots. I t is not stable between 1150 and 1300°C, but is thermodynamically unstable a t all temperatures.' However, like metastable carbon monoxide solid, it can be quenched from the gaseous phase. Both carbon monoxide gas and silicon monoxide solid will disproportionate upon heating above room temperature, especially in the presence of appropriate catalysts, hut properly prepared silicon monoxide solid can be retained a t room temperature indefinitely. Leo Brewer University of California Berkeley, California 94720 'Brewer, L., and Greene, F. T., J. Phys. Chem. Solids, 2, 286 (1957). 686 / Journal of Chemical Education
A Calendar of Science and Technology
To the Editor: Louia d. Kirrchenbaum's excellent suggestion [J.Chem. Educ.. 52. 193(197511of introducin~chemical history into the gdneral chemistry course by u& of hirthdays a i d anniversaries is a technique that I have been using successfully for the past two decades. Although a calendar listing birth and death dates of chemists was published in this Journal almost forty years ago [Huntress, E. H., J. Chem. Educ., 14,328(1937)], a calendar listing events from science and technology, with emphasis on chemistry, as well as events involving political and cultural implications of such events has not been available. About a decade ago, I began collecting items, complete with references, for such a calendar from books, journals, newspapers, and documents. While many of the listings (as many as ten for a given day of the year) are discoveries or inventions of the first magnitude, some are marginal items of much lesser significance which are provocative for further discussion, investigation, or research. Although so far I have been unsuccessful in getting the calendar published, Chemistry has published excerpts from i t for the complete month of April [Chem., 48(4), 23(1975)] and plans to publish more limited excerpts through next March. George B. Kauffman California State University, Fresno Fresno. California 93740
The Invention of the "N6nio" To the Editor: In an article published in this Journal [45, 75 (1970)], Bray refers to the theory of the vernier, stating that it was invented by the Frenchman Pierre Vernier. That is not the case. Actually it was invented by the Portuguese mathematician and astronomer Pedro Nunes (1502(?)1577(?)). He studied at the Universities of Salamanca, in Spain, and Lisbon, in Portugal, and he was Portugal's Royal Cosmographer. Nunes made an instrument for the measurements of angles and one of his students, the jesuit Cristovao Clavio. imnroved the orieinal instrument (in Portuguese and ~ ~ a n i sspeaking h countries it is called "nbnio," a name that derives from "Nunes"). Pierre Vernier (1'580-1637) lived in Spain for some time and probably came across the "nanio" there. Later he developed it into its nresent form. There is a short bioera~hv .. . . of Pedro Yunei in the Enc?clopnt din l3rito,r,rrr.o, and a more extensive one in the 'Crnnde Enciclooedid I'ortucuesa-Hrasileira" (Editorial Enciclopedia, ~ i s b b ea Rio de Lneiro). Aecio Pereira Chagas lnstituta de Quimica Universidade Estadual de Campinas Caixa Postal, 11711 13.100 Campinas (S.P.) Brasil ~
~
Review of "Environmental Pollution" To the Editor: I would like to correct a mistake in mv review of "ChemL. Pyle istry and the Technological ~ a c k l a s h ; bJames ~ which appeared in J . Chem. Educ., 51, A453 (1974). The book "Environmental Pollution" by Laurent Hodges has been reviewed bv Harold W. Kohn IJ. Chem. Educ., 50(9), A461-2 (1973)l. Anyone who is planning to offer an upper level course on environmental chemistry should consult the review for a thorough and fair evaluatioi of Hodges' book. J o h n W. Moore, Center for the Study of Contemporary Issues Eastern Michigan University Ypsilanti. 48197
