in quantitative emission spectrography itre accomplished through the use of graphical-type calculating boards which employ rectangular coordinate scale8 to convert per cent transmittance or density readings to the required logarithmic intensity values. Many variations of this type of calculator have been described iu the literature and are available commercially, Some of which are designed to utilize directly charts made on a particular recording densitometer. Because cost and limited utility of certain of these commercial types are important, especially where nonrecording densitometers are used, the present sliderule calculator (Figure 1) was designed and constructed. It provides the necessary scales for making the essential spechchemical calculations in a portahle, compact unit a t %minimumexpense. ALCULATION~
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The log scale was drawn on the circumference of disk B with the aid of a drafting divider; suitable short diatances were measured with the instrument on any desired length of a straight-line log scale, and this increment was transferred to the disk oirmmference. The smallest increments taken will produce the mast accurate disk scale. It is not essential that the log scale extend completely around the circumference of the disk, although in the interests of good appearance and maximum distance between scale divisions this has been done. The calibration scales are prepared with the assistance of the emulsion calibration curves drawn on semilog paper. The highest practicable per cent transmittance value from the paper plot is drawn on the smaller disk scale opposite the index on scale B (98% T opposite 1 in the figure). While the two disks are maintained fixed with respect to each other. the vernier arm is moved t o the relative intensity value on disk B corresponding to a transmittance of 96% on the graph paper plot. A scale mark is drawn on disk C representing 96% T. Successive repetitions of this procedure every 1 to 2% result in the complete calibration curve being transferred to the disk scale. The becuraoy with which such a oaloulator can be used is governed chiefly by the length of the scales employed. This rule may be expected to provide reading accuracy comparahle to a large calculating hoard, since an equal length of scale is coutsined in B smaller working mea. The unit is also adaptable for use in place of the Dunn-Lowy type of calculator when i t is desired to convert per cent transmittance figures far an analytical line directly into per cent coucentration. In this application a separate disk may be used to support two three, or more analytical line dopes. Automatic Spectrophotometry of Paper Strip Chromatograms. T. V. Parke and W. W. Davis, Lilly Research Laboratories, Indimapolis, Ind. spots on a paper strip chromatogram have been detected by miombiological aotivity, fluorescence, reactivity with a reagent, or ultraviolet or visible light absorption. Several devices have been described for spot detection using light OMPONENT
Figure 1. Spectral
The circular slide rule consists moving independently on a c e n t i , ___l. disk, B, contains B %cycle logarithmic scale around its circumference. The smaller disk, C, has similarly located per cent transmittance scales, which are in effect the emulsion calibration curves for the indicated emulsion type and wavelength region, A movable vernier arm, D, allows for setting the scale index and determining the desired relative intensity far any given per cent transmittance value. Construction of the slide rule has made use of heavy whitebacked cardhoard, which is convenient for lettering the scales with India ink. The vernier arm is of transparent plastic with an engraved hairline for accurate positioning. New disks are readily prepared when emulsion calibration changes e k e this necessary, although a single disk may contain several calibration scales on its surface. This is illustrated in Figure 1, where disk C contains calibration scales for an Eaatman S.A.-1 emulsion a t both 2800 and 3950 A. A variety of scdeles may be easily prepared by using any suitable duplicating process to provide paper impresFigure 1. Paper Strip Chromatogram Scanning Device sions which are subsequently affixed t o a durable disk material In -ition for n e e in Cery recording *pscfroPhmometer such as wood, plastio, or metal.
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