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APPARATUS FOR THE DEMONSTRATION OF CONDUCTIVITY OF ELECTROLYTES HANS A. SUTER1 and LORRAINE KAELBER Rollins College, Winter Park, Florida
THE
aDDaratus for the demonstration of t,he ..
electric conductivity of aqueous salt solutions consists the of a small flask or a test tube illdo ,,,hi& is solution t o be examined, and t,wo metallic conductors which are d i ~ ~ into e d the solution. If the solution contains an electrolyte the gap betmeen the conductors is short circuited and the flom of current can be detected by suitable means, i. e . , by the lighting u p of a light bulb. I n order t,o shorn the effect of different compounds or the effect of dilution on conductivity, either a series of flasks is necessary or the flask has t o be emptied and refilled with the new solutions. This procedure is not only cumbersome, but the continuous, gradual decrease ~~
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'Present address:
Celanese Corporation of America, Clark-
wood, Texan.
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A , oopper wire: 8.water inlet: C, powder Rlnnei: D. rubber stopper; nater drain.
of conductivity of salt solutions with dilution is diffirnlt show effectively. The apparatus which is described below is very simple and readily assembled and does not have the d i d vantages mentioned above. Furthermore, it is believed that it sholvs the conductance by electrolytic solutions much more impressively than does the usual setsup. The apparatus is shown diagrammatically in the figure. The center glass tube serves as the drain. On the portion of this glass tube inside the furlnel are wound two lengths of copper mire. The proper distance between these two loops is determined hy the eonductivity of the local tap-water supply. The wires are connected to an electrical plug in series TI-it,ha lightbulb socket. The funnel is supported by an iroo ring secured on a ring stand and the water inlet tube is held by a buret clamp. To show elertrolytic conductivity the vater is turned on and allowed to flow a t a moderate rate through the funnel, and the d u e is connected to an a.-c. outlet. The light bulb shouG not light up if the gap hetweerr the two copper leads is properly adjusted. The addition of a small quantity of an electrolyte, such as sodium chloride, t,o the flowing water in the funnel will light the lamp after a short interval required for dissolution of the salt. As the salt solutiou is diluted eontiriuously by the incoming water the light inteusity decreases, thus showing the dependence of rondurtivity on the concentration of electrolyte. The effect of different substances on the conductivity of water ran readily he demonstrated by adding any substance desired t,o t,he flowing water in the funnel and observing the light intensity of t,he bulb. As soon as a substance is flushed from the funnel a new compound can he added without any manipulation of t,he equipment being necessary. The apparat,us as described was designed as a demonstration-for a puhlir srienre show and proved t,o be very successful. $0
