W. H. Slabaugh
Photometer
Oregon State Univers~ty
Corvallis
Instrument for the freshman laboratory
The photometer is simply a device that measures the intensky of light passingthrough a chemical system by means of a self-generating photocell. The electrical circuit is similar to that of several commercial instruments, but certain refinements such as filter holders and sample storage compartments have been omitted. The instrument shown in the figure was constructed of plywood and is approximately 4- X 5- X 10 in. This photometer is well adapted for quantitative experiments such as the photometric titration of copper(I1) ion with ammonia and the reaction rate characteristics of the decolorization of crystal violet by hydroxyl ion. Other reactions involving changes in optical density are also adaptable, particularly with the addition of appropriate filters. The simplicity of the instrument permits the student to see the principle of its operation as he uses it. EDITOR'SNOTE: Probably readers who h e w had the experience of similar demands on ingenuity to replace funds will he ahle to contribute to a series of articles on this theme. We solicit only descriptions of imtruments proven to be satisfactory by lahora40, 641 (1963). tory use. See also THEJOURNAL
12
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Journal o f Chemical Education
~ a r nList
Photocell, selenium or silicon solar cell; Radio Supply $5.50 Outlet Millimnmeter, DC, range 0-1 ma; Government surplus 1.00 Potentiometer, 1watt, 5W ohm; Radio Supply Outlet .96 L m n . 110 VAC. Medium Screw bsse. 50 watt .35 ~ssc.&ceptaclefor lamp .20 Plywood, hardware, 18-2 appliance cord, cord cap. .60
L' \Light Shllid
A Studen1 Phommeter.
