Nomogram for the computation of the corrected colour value in 17-ketosteroid estimation by the Zimmerman reaction.

This formula, derived largely from the work of Talbot, Berman, and MacLachlan (1942), can easily be converted into the form x=mly+m2z which allows the construction of a simple nomogram (Feldman, 1935). The latter greatly accelerates calculation when several estimations are being done together, and reduces the risk of arithmetical error. Thus if the observed extinction at 430 mu=E430=x, the observed extinction at 520 mru=E,5,=y, and the corrected extinction =E (corr.)=Z, the formula given above can be written: y=0.73z+0.6x..... .... (2) To construct a nomogram. of sufficient accuracy take a large sheet of 1 in. graph paper (20 in. by 15 in.), scaled in 1/10 inches, and draw three parallel vertical lines, 15 in. long and 5 in. apart and a base line along the bottom as shown in Fig. 1, and label the vertical lines X, Y, and Z, from left to right. On X will be plotted the observed E43o and on Y the observed E&20, and Z will then give E(corr.). The line X is marked off in 2 in. divisions, each to correspond to 0.1 unit. It is subdivided further and at the point 0.730 unit a line is drawn parallel to the base to cut Z and this point is marked 0.600 unit and the length between the point and the base is divided into six equal divisions and subdivided further and also extended a little way upwards as shown. In order to graduate line Y, tie-lines are placed between point 0.300 on X and 0.301 on Z and where Y is cut corresponds to 0.400 unit on this scale. Similarly by joining point 0.600 on X and 0.603 on Z the point 0.800 is found. Confirmation of the above points can be obtained by joining 0.500 on X with 0.137 on Z and 0.700 on X with 0.521 on Z, after which Y can be divided into eight equal divisions and further subdivided. The main X, Y, and Z lines and their divisions are best traced on to a sheet of white Bristol board by pricking through the marks with a sharp needle after which the nomogram is drawn on the cardboard in Indian ink.