PORTABLE CONDUCTANCE AND FARADAY'S LAW APPARATUS FOR GENERAL CHEMISTRY RICHARD B. CONKLIN, STEPHEN P. MARION and DONALD D. WRIGHT Brooklyn college, Brooklyn, New York
T m s NOTE outlines the major features of two portable pieces of apparatus, easily constructed by an instructor or college shop, which have given over six years of excellent service in general chemistry courses a t Brooklyn College.
Figun, 1.
of range 0 to 200 mamp., a &volt, 0.25-amp. radio pilot light with jewelled hullseye, and a momentary pushbutton switch, all mounted in the box top; and two projector-type graphite electrodes, 6 mm. X 6", mounted in the assembly visible on the left aide of the box. The L-shaped piece of ~ o o dset , with its bottom 6 inches from the base of the box, acts as a beaker stop to insure constant electrode immersion during measurement, which is routinely done with 50 ml. of test solution in a 150-ml. beaker. Both electrodes, held in their brass sleeves by set screws, are capable of vertical adjustment, and the horizontal distance between them may likewise he adjusted. The apparatus has proved outstanding in cheapness and durability, and gives sufficiently accurate results for general chemistry work. The function of the Faraday's law apparatus, illustrated in Figure 2, is to distribute safely from a 110volt d.-c. line outlet a limited and measured amount of current simultaneously and independently t o each of the groups of electrolytic cells being operated on one laboratory bench. The desired number of similar units connected in parallel are mounted in line on a board, measuring abqut 1' X 1' X,.ll/r" per unit, which rests on the laboratory bench. Each unit contains an inexpensive Readrite ammeter of range 0 to 1amp., a 60mat.t, 110-volt lamp, a double-pole, single-throw knife snitch, and protruding leads of convenient length, made of single conductor, rubber covered, flexible wire, and ending in st,andard 2-inch batter? clips to which are fastened the cell electrodes. The concealed connecting wiring is single conductor stiff wire, and the lead to the
Conductanoe Apparatus. Front View. Showing Rsan Panel i n Partidly Raised Position
The apparatus illustrated in Figure 1 is used to measure the relative conductances of various types of electrolytes. The box, of internal dimensions 9" X 53/aN X 51/4"and provided with a rear panel sliding in grooves and held in the closed position by one screw, contains four dry cells, size number six. The series circuit compries these cklls, an inexpensive Readrite milliammeter 393
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polarized plug connecting with the building line is allrubber cord. If desired for pedagogical reasons, the wiring diagram can be traced by paint on the top of the
JOURNAL OF CHEMICAL EDUCATION
board. The apparatus is rugged and foolproof to a high degree, and no injuries have been incurred in over six years' use with hundreds of students.
