Computer Drawn Diagrams-An
Aid for the Non-Draughtsman
It has been noted by the author that several computer programs bave appeared in this and other journals. They purport to perform a wide range of tedious arithmetical tasks and will return values for stability constants, molar absorbance~,kinetic parameters, e t ~ The . algorithms employed are invariably supported by the basic goal of minimizing the difference between sets of observed and calculated results. Too frequently, however, the results are not supported by diagramatic evidence as to the "goodness of fit." Many computer installations have access to a CALCOMP plotter and the intelligent use of this and the related software can provide, at a glance, invaluable information often hidden by the sheer weight of numbers produced. Six related plotting packages bave been written; five for the plotter and one for the 132 character printer. They will ~ e r f o r mthe following tasks: (1)Plot observed and calculated spectra and on a separate diagram show the calculated molar absorptivities Tor each light-absorbing species. (2) Provide a smooth curve through a set of experimental points. (3) Draw continuous variation curves. (4) Plat any set of data for either incremental or nonincremental values of r (or y). This requires two programs. Two examples would be a molar ratio diagram, given incremental values of CL/CM, and a titration curve, where the volume of added base is nonineremental. An example of the CALCOMP output is shown in Figures 1 and 2. Figure 1 is a plot of the molar absorptivities of the three species produced from the interation of ~icaline-2-aldehydetbiosemicarhazone (PATS) and protons. Figure 2 shows some calculated (solid line) and experimental spectra used to evaluate the pK,'s of PATS.
L Figure 1 An example of computer drawn species spectra
Figure 2 An example of experimental and theoretical spectra.
The "printer-plot" routine represents a considerable saving in time since turnaround far the CALCOMP plotter is frequently ten times slower than the printer output. Core requirements for this routine are minimal (-300 bytes). A peripheral benefit of these routines becomes apparent when diagrams are to be included in a publication. Packages (2) to (4) enable the production of a wide variety of high quality diagrams where the services of a draughtsman are not available. It should he pointed out that none of these routines perform any calculations other than those necessary for actual dotting. Fitting the best straight line etc. would he performed by any suitable program that the user will have available. Listings, sample output, and relevant details for these Fortran programs are available from the author on request.
D. Leggett University of Waterloo Waterloo, Ontario, Canada
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Journal of Chemical Educafion
