NOVEMBER, 1950
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FLAME TESTS IN THE PRESENCE OF SODIUM RICHARD 8. HAHN Wayne University, Detroit, Michigan
THEblue cobalt glass filter used to make flame tests Limit of Sensitivity of Flame Tests in the presence of sodium is not altogether satisfactory. Lowest obswvable concentration in parts per million Part of the spectra emitted by elements other than soCobalt glass Didymium glass dium is also absorbed by the filter, which changes the Ion Tested No flte?. filter filler characteristic color and also decreases the sensitivity of 1 loo0 1000 Na+ the test. 100 100 100 K+ A didymium glass filter serves the purpose much 10 100 10 Li+ 100 1000 1W Ca++ better than the cobalt glass; it transmits the light un100 1000 100 src+ changed in color and practicauy undiminished in intenBz++ 100 10,000 100 sity. The transmission curves show the selective absor~tionof the sodium lieht by the didymium glass cokTRPINSMtSSION CURVES OF D l D I M l U M AND COBALT GLASS FILTERS pared with the wide absorp100 AND F L b M E SPECTRA O F VARIOUS E L E M E N T S tion range of the cobalt glass. The characteristic limes of the flame spectra of some common elements are plotted on the same scale at the lower portion of the chart. A study of the limit of sensitivity of various flame tests was made. The results are given in the table. Didymium glass filters (Didymium No. 512) are available from the Corning Glass Works, Corning, New York. For effective absorption of sodium light, the filters should be a t least 4mm. in thickness. A didymium glass filter 5 cm. square costs about two dollars.
