factor to the experimental f.i.d. spectrum in order to improve the signal-to-noise ratio in the transformed spectrum may be observed. The consequent loss of resolution is readily seen. Other values for the parameter SE may be used to give reso- lution enhancement.

This seauence of units has been used effectivelv during .ectures i n J course ,,ti principle> and applicariona or Feu- ritr-transiurm UhlH trc,hniuuc. The students then use the program in their own time to obtain more experience of the way in which the variations in parameters affect the experi- mental spectra. A single-page list of instructions is provided

theinstruction sheet, are available from the author upon re- quest. A check for $10, made payable to the University of Canterbury, should b- included.

Drawing of Ball and Stick Type Molecular Models with Hidden Line Elimination

Hidehiko Nakano, Osamu Sangen, and Yoshitake Yamamoto Himeji institute of Technology Shosha, Himeji 671-22, Japan

Some programs have been reported for drawing of molec- ular structures by microcomputers (1,4) but these programs do not eliminate hidden lines. therebv increasing the realitv of drawings. Preparation of a with lhidden line elimination according to the same algorithms as are utilized - "

with mainframe computers is difficult due to the limitation of memorv size and calculation soeed. We have develo~ed a simplified algorithm for drawing ball-and-stick m o l e h a r structures with hidden line elimination, and oreoared a oro- . . Cram adaptable r u low cost m i c n ~ c ~ m p u t ~ r swems.

This vrunram. written in 11.2SI<' with about :380ataremrnu. consist; of% functional units

1) Inout data for atomic coordinates and connection table from keyboad

2) Write data to cassette tape or floppy disk files 3) Read data from the files 4) Print data 5) Rotate the molecule 6) Draw the molecular structure by perspective projec-

tion.

The program is now implemented on three hardware systems: SORD MlOOACE (48 kB, dual mini-floppy disk drives)

Figure 6. Structure of cyclohexane plotted on Watanabe platter by SORD MlOOACE com~uter.

equipped with Watanabe Instruments WX4671 low cost X-Y plotter, SHARP MZ 80B (64 kB, 320 X 200 dots graphics, single cassette deck), and Apple I1 Plus (48 kB, single mini- floppy disk drive). Examples of the drawings of cyclohexane by two systems are shown in Figures 6 and 7. The time re- mired for drawing cvclohexane is about 5 min (M100ACE ~~ ~

system), 40 sec ( M i 80B system), or 75 sec ( ~ ~ ~ l e ' 1 1 system). Molecules of about 100 atoms can be drawn by the MlOOACE system, while more than 200 atoms can be displayed by the MZ BOB or Aoole 11 svstem from astandooint of the memow- size, althoughihe resdution of the dispiay will then become a limiting factor.

This program can be easily adapted to a system that is equipped with hardware to output graphics (such as X-Y plotter of high resolution screen graphics) and with a BASIC statement for drawing a line between two specified points. A statement for drawing a circle is desirable but not essential. Listings of the program are available on request, handling charge $5 (International Money Orders in the name of Hide- hiko Nakano).

A Simple and Inexpensive pH-stat and Autotitrator Based on the Apple II Plus Computer

Richard D. Cornelius and Paul R. Norman Wichita State University

Wichita, KS 67208

The research in our laboratory frequently requires the measurement of DK values of coordination comulexes, and the maintenance of pH during reactim kinetics. In view of the popularity of the Apple I1 Flus comduter, and the availability of supporting hardware, we selected this microcomputer as the basis for a time-saving automated pH-stat and titrator.

The system that we constructed utilizes an Orion pH-meter with BCD o u t ~ u t to monitor pH changes, but could readily be adapted td other p~-me<ers. he-computer-controlled addition of acid or base is accomplished using a glass syringe mounted in a micrometer syringe drive which is advanced by a stepper motor. The software is written entirely in BASIC so that it may be easily and quickly modified and the hardware construction is simple in design. The system has proved very flexible. both as a oH-stat and titrator. due to the ease with which both the software and the hardware can be changed to suit different experimental needs. The apparatus can titrate as little as 1.0 ml of a 10 mM-solution of a dibasic phosphate (2 X 10Vmoles of H+) and give extremely consistent pK values. Our purposes are served with a 1.0 ml tuberculin sy- rime in the svr in~e drive so that acid or base addition can oc& in increments of as little as 0.043 p1. The scale can be

Figure 7. Structure of cyclohexane displayed on screen of SHARP MZSOB wstem.

98 Journal of Chemical Education