In the Spring of 1946, after 9 years of making routine qualitative spectrochemical analyses by means of David Richardson's "moving plate" method (1), it became necessary to make determinations of metals more accurately with small increase in the time required. For various reasons, part-time research was devoted to developing the details of a semi-quantitative method that could be applied to any type of sample that might be submitted. The moving plate method excellent for general sensitivity and very positive in identification, left the estimating of concentrations entirely up to the spectrographer's experience, judgment, and memory. He had only the varying width, density, and length (which is sometimes discontinuous) of a photographic line image to integrate into a single value, to which he applied mentally the charge in the electrode and a least detectable (L.D.) concentration for "average" conditions of matrices for each line found. This rough and personal method necessitated the use of large tolerances when reporting, and in this laboratory it was found very convenient to have tolerances of 10-fold, with 10-fold steps between estimates and a 10-fold overlap up and down. This can be seen as used in the tabulation form shown in Figure 1. This method of numerical symbols gave a unit step relation among all determinations and made comparisons easy at a glance. The symbol number is 3 greater than the logarithm of the "log average" of each range in ppm. "Log average" here used means the concentration that is the anti-log of the men of the logarithm of the extreme concentrations of the range. Viz., 4 is 3 greater than 1 which is the logarithm of 10 ppm which is the "log average" of 100 and 1 ppm, the extremes of the concentrational range for the symbol. The addition of the integer "3" prevents the appearance of negative symbols.
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