The ALLOCAT program selects two unknowns per student utilizing the entire master file. Each compound has a chance of being allocated only once. Anumbered and labeled list of the selected com~oundsis printed for use by the storeroom personnel. A; additional numbered listing of compound information is printed for the lab instructor. This includes the melting or boiling point, formula, functional group present, type of compound, and any nomenclature synonyms. Figure 6 shows an example. The number of compounds chosen hy type and functional group is also printed. The selection process creates a sequential access file "Second.has" that is needed in the mixture allocation process. The ALLOCAT program selects compounds for "unknown mixtures" taking into account the two previously allocated unknowns. Because separation is accomplished by aqueous extraction, only those compounds that are water insoluble and ether soluble are eligible for the mixtures. Approximately 60% of the compounds in the file met this criteria. Each of the eligible compounds may he used twice during the mixture selection. Another parameter for mixture distribution allows only the combinations of strong acids, weak acids, bases with neutral compounds, and bases with weak acids. Because of incomoatihilitv nrohlems amines and aldehydes are not combinedin an '&known mixture". A counter included in this section allows the program 750 tries to find a suitable mixture match. If no match is possible, this information is recorded for that mixture numher. This menu selection also produces a storeroom listing and an information listing for the instructor. At the berinning of this selection, the requests a name for the file that will store the names of the four compounds given to student #1, #2, etc. Additional copies of all listings can he obtained through the PRINTOUT program. The sequential access file created by allocation of the mixtures is called 'Mixlist.has". One complete cycle of the program with approximately 200 compounds in the "Unknown" file produces four compounds each for approximately 75 students. Requesting more matches than this creates problems in finding suitable compounds to make the "unknown mixtures". The program can he run several times to produce alarge numher of comhinations. Options from PRINTOUT include hard copies of the entire"unknown7' file with all information, a &ing of only one functional group, a copy of the entire file by functional group or type, and a listing of the compounds availahle for the mixture allocation. Additional copies of storeroom listings and instructor information plus compound listing of any previous sessions run are also availahle through PRINTOUT. A printed copy of the compound file, "Unknown", is necessary to make corrections t o any of the previously entered data. The total numher of compounds by type and functional group is included in the master listing, along with any dropped and unusable compounds. The program was designed to run on IBM-PC's or compatibles usiue PC or MS-DOS. one disk drive. and a orinter. The SETUP, ALLOCAT and PRINTOUT piogramdoccupy 22.000 to 26.000 hvtes of disk space: DOCU 14.000 hvtes: SCREEN 5,800 bytes, and the ~ N T R Omenu 1;200 bytes: The numher of bvtes used hv the secluential access files created during program execu$on depends on the numher of student compounds requested. One file (First.has) created as the program runs is eventually erased, and files "Second.has" and "Mixlist.has" remain on the disk until that particular selection is run again. The length of the "Unknown" file containing the compound information depends on the number of compounds entered. For approximately 200 compounds the file occupies approximately 26,000 bytes. The authors wish to thank Stephen Gates, Department of Chemistry, Illinois State University, for his programming assistance.
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240
Journal of Chemical Education
Color Images of Molecules John J. Farrell Franklin and Marshall College Lancaster, PA 17604
After reading Viewing Molecules with the Macintosh by Earl J. Kirkland (11). I was inspired to write a similar program for the IBM PC in color. COLOR3D.BAS is a BASICA -aroeram for anv IBM PC with a color monitor. The orwram draws three-dimensional images of complex molecules. The user must s u o ~ l va file that contains the followine information for each atom: anumher corresponding to t h e h o r to be used, the x,v,z coordinates (in anastroms), and the radius (in angstromsj. The molecule is displayed with hidden surfaces hidden. Each type of atom is dis~lavedin its designated color or color $&tern (carbon in bluk, hydrogen inwhite, boron in magenta-and-white check, and so on). The molecule can be rotated about two axes (the azimuthal and polar axes on the screen). The user can supply a viewing distance (from the molecule). I t takes the computer 20-40 seconds to draw a molecule. The program can he used in chemistry courses to depict conformation of molecules, effective and ineffective collisions, elements of group theory, and unit cells of crystals. A more detailed description of the program and some color pictures of the images generated can he found elsewhere (12). A 5Y-in. floppy disk that contains COLOR3D.BAS, seven files for various molecules, a listing of the promam, and a complete description of the program and howto use it, is availahle from the author. Send a check for $20, payable to the author, to cover the cost of materials, postage (domestic), and handling. Also, COLOR3D.BAS is availahle for downloading from BYTEnet listings a t (617) 861-9764. You will need an IBM PC or PC compatible with BASICA and an RGB monitor to run the program.
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A Cammodare ~icrocomputer/~ettler 440
galanee Interface &in
Harvey F. Blanck Peay State University Clarksville, TN 37044
While some digital laboratory devices are specifically designed to interface easily to computers by providing digital information a t a socket or edge connector, many do not. However, the information sent to the LED display unit may in some cases he easily intercepted and sent to a microcomputer. As an example, I will describe an interface used to obtain data from a Mettler 440 electronic toploading halance. The digits are displayed sequentially and repetitively a t a high enough rate that they appear t o he on continuously. This refresh cycle is controlled by a microprocessor output with one dieit select line for each of the six ~ossibledigits and one line for each of the seven segments forming t h e digits. In the interface to he described the microcomputer sorts out the data after acquisition. This method avoids latches and results in a dramatic reduction in the amount of hardware and time needed to construct the interface. In this example i t is possible to reduce the information necessary per reading to eight lines. The data from the sixdigit select lines may be reduced to three lines using a 74C10 chin. .. which is a tri-three inout NAND eate (Fie. . - 7). . Although digits may require up to seven segments for visual disolav. . " . onlv five a m r o ~ r i a t e l vselected segments need he monitored to distinguish between each of
