Modlflcatlon to LED Colorlmeter To the Editor: The LED calorimeter described by W. W. Wendlandt (J. CHEM. EDUC., 53,134 (1976)) can be improved by the following small changes: Mount the electrical connections on the lid at the end remote from the test tube holder. This eliminates the long flexible leads shown, and the need to manouver the circuit board past the rear ends of terminals if it must be removed from the box for any reason. Invert the printed circuit board, and fasten it to the underside of the lid, "stood off' by suitable washers, and held by the potentiometer mounting, the shanks of the electric connectors mentioned above, and the woodscrews which hold tht! hlnrk for the test tuhe.'l'his allows the entirecir~uit111 be I~fteduut with thelid,and to beassembled mureconveniently
66 / Journal of Chemical Education
and auicklv. Possiblv more imoortant. it keeos the circuit components at the top of the box, away from the contents of the occasional ill-wioed test tube. or tube broken bv careless insertion. The holeto admit the test tube must 6e drilled through the circuit board, and should pass completely through the block to allow drainage of spilled liquid. If desired, a disc of cork may be cemented to the box bottom as a rest for the test tube. Blackening the boreholes in the wooden block with matt paint or textile dye teaches a gwd point, and may prevent some anomalous effects from odd reflections.
I!niversity of Waterloo Waterluo. Ontario. Canada M I . X I
