VOLUME 33, NO. 9, SEPTEMBER, 1956
445
A DEVICE FOR DEMONSTRATING CONDUCTIVITY OF SOLUTIONS FRED 8. EISEMAN, IR. John Burroughs School, St. Louis, Missouri
AN APPARATUS has been developed that makes it pos- hazard, and prevents contamination of samples. It, sihle t,o demonstrate the conductivities of solutions mithout destroying, transferring, or contaminat,ing them. The device can he stored with the solut,ions and is ready for instant use. A representative series of solutions is contained in large test tubes in a rack. Pairs of graphite electrodes wired in parallel are inserted in two-hole st,oppers in these test tubes. One lead from each tube passes to a selector switch. Provision is also made for testing open containers of solution by inrluding an uncovered pair of elertrodes. Indication of conductivity is given by the brightness of a lamp a t the top of the control box, as well as by a panel meter. Binding post,^ are provided for connection to a projection meter. The device operates on a line voltage of 117 volts a. r. This equipment has proved to he superior to the rommewially available porrelain-collar devices with project,ing wires hecause it obviates the necessity of preparing ne\v solutions each year, eliminates shock
appears to have the advantage over a device described by Ahrahams, Blitzstein, and Luborskyl in that the conductivity of the solutions can he tested individually. A unique feature is the use of grid caps and clips for connect,ion to the carbon electrodes, as ran he seen in the figure.
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ABRAHAMS, H. J., W. BLITZSTEIN, A N D F. LUBORSKY, School Science and Mathematics, XLIV, N o . 8, 730 (Piov. 1!>44).
Schematic Diagram of c i r c u i t
Only two of ten standard test tubes are s h o r n . 1, SPST power switch. 2. SPST external-meter switoh. 3, DPDT switch for eonneoting to msealed
eleotrodea: position A, unsealed electrodes: position B, 10 standard aolutiona. 4. 10 position and off,power t a p switch for eonneotina to each of the ten standard cells. A , 0-I-amp a:o. panel meter. L. 1 8 - r a t t , clearenvelope carbon-filament incandescent l s r n ~ .
