Tested Overhead Projection Series Compiled by HUBERT N. ALYEA Princeton Universitv
TOPS 1970-SUMMARY A summnry of chemicals, devices, and projectors (1970 models) is an appropriate ending to this TOPS series, begun in 1962.
TOPS PROJECTORS-1970 Three make-it-yourself TOPS projectors serve different purposes. See Figure 3. 1. Lensless Projector. For schools dependent on battery pox-er. A single filament automobile bulb (No. TS-1133 or TS-1183) is painted with a heat-resistant (auto engine-head) lacquer, leaving a '/%-in. clear spot in the center. If the bulb is attached to a battery (or a battery charger) of the proper voltage it acts like a "pinhole" projector: no lenses are required. The reaction cell is placed a few inches in front of it, and a screen or 20 X 30 cm sheet of wax paper a few inches further forward.
Convenient for student use in the laboratory is any high-intensity reading lamp (cost between $7 and $20) running on 110 V ac converted to low voltage, with its bulb similarly painted. 8. Student Darlcroom Projector. I t uses a 150-W 110-
or 220-1' ac flood lamp. Excellent for the teacher with limited budget since there are no replacement costs, the $1 bulb lasts 2000 hr, and there is no fan to wear out. 3. Daylight Projector. It uses a 650-W quartz-iodine lamp operating on 100 or 220 V ac. Note the addition of a rectifier to prolong its 80-hr life to 1000 hr.
The latter two projectors have three parts: the stage, the lens-mirror assembly, and the light-box. Their construction is outlined below.
STAGE Materials. Plastic Fresnel lens cut to 5 X 5-in. size. This, together with the two glass lenses mentioned below, can be purchased for $9 from the Edmund Scientific Co., Barrington, N. J. 07008; specify the TOPS lens Kit. Transparent acrylic plastic (Plexiglas, Acrylite, etc.) as follows. Front plate, 51/2 X 5l/4 X '/a-in. Back plate, 5'/% X 5 X l/s-in. ExBase 5l/2 X 2a/a tension stage, 5'/2 X l l / z X X '/a-in. Top, 5'/% X X I/+-in. Extension stage brace, 51/2 X 1 X Il4-in. Note that the last three pieces are '/&-in.thick; they can be made by cementing two I/&. pieces together. Assembly. (a) Cut a grove about '/s-in. deep in the middle of the 5l/%X 15/8 X I/i-in. top piece; this will
MODELS
support the lens. (b) Cut t ~ v ogroves in the base, one grove 'a/la-in. from the edge, the other 15/~-in.from the edge: these will align with the grove and back edge of the top. (c) Cement all plastic pieces together. To do this, run a drop or two (no more) of very thin acrylic cement along the juncture of two pieces and hold them firmly together for a minute; capillarity pulls the cement into the juncture. (d) Finally slide the plastic lens into place, but do not cement it.
LENS-MIRROR ASSEMBLY. Materials. (a) Two glass lenses, plano-convex, SF mm dia., focal length 571 mm; available from Edmund Scientific Co., see above. (b) Two rear-surface mirrors, 5'/2 X 4in. and 51/2 X 3'/%-in. (c) Butterfly hinge with base about 3-in. long and triangular part 4-in. long. (d) Silicone cement for fastening mirror to hinge. (e) Six solder-lugs, with screws, for supporting lenses. (f) Nails and glue. (g) Six pieces of wood as follo\vs; all but the top can be of plywood. . Base, 10 X 5'/z X 3/s-in. Two sides, 5 X 5 X a/s-in. Back, 6 X 5l/% X Stop, 4 X '/& 3/s-in. Top, 6 X 5 X '/%-in.
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Assemblu. (a) Cut a 87 mm hole in the top piece to accommodate the glass lenses. Using a 1/4-in. strip of cardboard to separate them, and the six lugs, anchor them in the top piece. (b) Gently hammer the hinge to damage it, so it is stiff. Screw its base on the top piece, behind the lenses; and cement the triangular portion to the back of the 5'/% X 3'/,-in. mirror. (If hinge or cement are unobtainable, devise a plastic or metal strip notched to hold the mirror and bolted to stiff 13/4-in.butt-hinges.) (c) Cement andnail the haw, sides, top assembly, and back together. ((1) Insert the 51/2 X 4-in. mirror a t a 45" angle inside, bclou the lenses, and anchor it in place by cementing and nailing the 4 X '/, X a/8-in. wooden stop agaimt it.
LIGHT-BOX FOR DARKROOM PROJECTOR Materials. (a) Nine wooden pieces as fol1on.s. (Size of the box is critical to achieve "chimney effect cooling"; do not try to improve cooling by boring vents in the box.) Top and base, each 18 X Fa/,, X l/,-in. plywood. Volume 48, Number I , January 1971 / A43
Two sides, each 18 X 61/a X '/tin. plywood. Back, X X a/s-in. solid. Four support pieces, each 18 X 3/s X 3/8-iu. solid. (b) Porcelain socket and 150-W, 110- or 220-V spotlight or floodlight. (c) Male plug. (d) Six feet of 2-wire extension cord. (e) SPST toggle switch. (f) Cement, screws, nails. Assembly. (a) Cement and nail the four support pieces along the edges of the two sides. Then cement and nail together the sides, top, and base. (b) Screw the porcelain socket to the center of the back piece; also bore a hole and insert toggle switch on this piece. (6) Cut off 1 f t of extension wire to be used later. (d) Attach the remaining wire in series to the socket, toggle sxitch, and plug. (e) Attach the back assembly to the box, boring holes and using screws so that it is removable for repairs. (f) Insert floodlamp. (g) Staple the wire against the Ense so i t ~villnot swing against the hot floodlight and scorch. (h) Bore t v o '/&-in. holes 6-in. apart on the top of the box, insert the ends of the 1-ft cord and knot both ends inside the box to form a carrying handle. (i)A suitable catch should be attached so that stage and lens-mirror can be stored inside the light-box.
LIGHT-BOX FOR DAYLIGHT PROJECTOR Mate~ials. (a) A wooden box 14-in. long, its crosssection determined by the size of the fan inside it. Be sure it is sufficiently large; ours !\-as 5-in. dia., and the box 6 X 6-in. (b) Toggle switch, SPST, 10 amp, 110 V. (c) Toggle switch, DPDT 10 amp, 110 V. (d) Extension cord vith 10-ft extension wire. (e) Silicone rectifier, 12 amp, 200 PIV. (f) Venturi fan, 5-in. dia. (g) Cement, nails, screm, bracket for fastening reflector and lamp to box. (h) Quartz-iod,ine 650-W, 110-V lamp and reflector: Edmund Scientific Co., see above, sell lamp reflector 3 lenses for $21. (i) Carrying handle. ( j ) Recessed male plug and female soclcet; male plug.
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Assembly. (a) Make a wooden box of '/&-in. plywood 14-in. long and of cross-section (6 X 6-in.) sufficient to accommodate the fan. The sides, back, and base should he cemented and miled to form one piece, and all electrical parts attached to this. The top should be removeable to facilitate making repairs. (b) Bore about eight 3/8-in. holes in the reflector so air can be sucked through i t to cool the lamp adequately. (c) Fasten fan and rectifier to the back, lamp and reflector to the base, the two switches on the side which will face the operator, and the recessed plug on the other side. (d) Solder wires to connect the electrical parts as shown in Figure 3; this circuit prohibits the lamp from operating if the fan is off, but allows the fan to continue cooling after the lamp has been turned off. Also the lamp can be burned a t half intensity (.55-V do through the rectifier) and turned on full (110-V ac) a t the peak of the experiment; this prolongs the SO-hr life of the bulb to 1000 hr. (e) A suitable catch should be attached so A44
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Journal of Chemical Education
that stage and lens-mirror assemblies can be stored inside the light-box.
USE OF TOPS MATERIAL. This concludes eight years of TOPS. Perhaps it would he well to indicate different ways it is being employed today. 1. Projection of Experiments. (a) For schools with very limited budget ($5 per year for an entire class). (b) To improve visibility for demonstrations to large classes. (c) To make it possible for the high school teacher, with no assistants, to be immediately prepared t o do countless experiments. 2. Arm-Chair Chemistry. For universities and high schools with enrollments so large that laboratory work has been abandoned, and replaced by lecture-hall demonstrations. Where the student does not touch a chemical the entire year. I n this case, the writing arm of his desk in the lecture-hall becomes his laboratory desk. Each student is given his own Student TOPS Kit, a 200 ml polyethylene bottle of water, a tray, a disposal bucket, and a set of reagents, replaced fortnightly. For example, with five 1-05. dropping bottles of reagents a laboratory exercise has been devised involving indicator color changes, standardization of acids and bases, determining the % of COz in the air and in the breath, determining the legality of vinegar, and showing that for a sharp end-point in a titration involving weak acids or bases an indicator must be chosen which has a pK matching the pH of the salt being formed. Cost for this 5-hr exercise for 100 stu~dents totals under $2.
As a Research Tool. For schools with adequate laboratory facilities, and for the exceptional student. The student uses a TOPS Picturebook (now available) to achieve positive results, which in turn suggest original experiments which he devises, suggests, and carries out. A set of 60 chemicals in 2-02. bottles is made available for every 10 students, and 8-02, refills suffice for an entire term for 100 students; the teacher does not have to go to his stockroom once during this period. The student is graded on the originality of his proposed research and how clearly he describes and interprets his results. For example, one student who electroplated silver suggested to electroplate out other metals, then a t different pH's, then for different lengths of time, then from complex ammines.
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TOPS then finds use today not only in its original media as a means for projecting experiments, but as a practical laboratory tool to be used by each individual student without a projector. This concludes the TOPS series. TOPS like TOPSY has GROWN UP!
Figure 3. TOPS PROJECTORS, 1970 Models. (a) Lenrierr Proiector. iector. F-Fan. L-Lomp. R-Rectifier. S-Swikh.
(b) Darkroom Projector.
(c) Daylight Projector.
(d) Wiring for Daylight P r o
