hold that the bulk of '"Ar on the earth is ofthe above radiogenic origin. On this assumption, they calculate the age of earth's crust from the ratio of 4oAr/'%. If this oriein of "Ar. which constitutes 99.6% of the total argon, is accepted, the Ar-K inversion in the periodic table is explained. A similar approach is not available in the case of the other two inversions. All naturally occurring cobalt is monoisotipic (''Co) and stable while all the naturally oecuring Ni isotopes are stable. Similarly one finds that all the naturally occurring iodine is monoisotopic (lZ7I)and stable, while the corresponding isobar '27Te is wholly synthetic. ~~~
H. J. Arnikar University of Poona Pune 411 007, India
BUFCALC Crash Corrected
Dear Editor: Afootnote to a paper that I published in the Journal of Chemiml Education ("BUFCALC: A Pmgrarn for the Calculation of Buffers of Specified pH, Ionic Strength, and Buffer Capacity", 1990, 67,150) stated that a copy of the compiled code for BUFCALC could be received from me by sendine a formatted IBM diskette in a ~ostaee-paidselfaddressed envelope. Since publication, I iave &&d dozens of reauests for copies of this Dromam. While the copies I sent o i t were tech&ally corkctIn terms of the b&er calculation, an undetected programming error would intermittently cause the program to crash. This error has been corrected in the most recent version of the program ( 3 1 1 Readers who havelad problems can receive the new version bv sending a diskette as before to my new address below. William J. Lambert
Pfizer Central Research Building 156 Gmton, CT 06340
Imprecise Numben and Incautious Safety Procedure Mar Experiment
To the Editor: I am writing with reference to the articles T h e Cadmium-Sodium Nitrate Reaction" ( I ) and T h e BismuthSodium Nitrate Reaction" (21, by Williani D. Hill, Jr., which appeared in the Journal of Chemical Education in 1990 and 1989, respectively. 1 have two questions regarding these articles, one relating to the use of sigmfkant figures, the other relating to safety.
the products (51.3627 f 0.00019) g implies a relative error in the mass of product of only 4 ppm. I have several questions about this data. The yield is (99.984 r 0.0004)%based on the stated mass of Cd. While there are manv reactions that proceed wantitatively, this level of pre&ion is startlingwhen pkducing transition metal oxides, which are notorious for deviations from stoichiometry. Apparently the author believes that neither CdO nor Biz03 suffer from this problem. My Cotton and Wilkinson, Advanced Inorganic Chemistry states that CdO varies in color with thermal history due to lattice defects so it is possible that at least the CdO composition could vary. I find it somewhat difficult to believe that the original samule masses were adiusted to aeree-within the ranee rep;esented by the prod&t ranges @.0005 gout of 50 g & 10 prim). Even if this level of re~roducibilitywas achieved, pe;
