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77 <br />• only under a reasonable load. <br />3.. Always keep the electrode wet, preferably in a <br />solution of saturated M. If this is not feasible, try <br />keeping the water in the protective cup that came with the <br />electrode. <br /> <br />4. The best way to use the rubber sleeve over the KC1 <br />filling hole on the electrode is to just pinch it open to <br />the atmosphere and not slide the sleeve down. One forgets <br />that the sleeve is down and leaves the electrode or packs <br />it back in its box. The result invariably is a dried up <br />electrode when a critical measurement needs to be taken. <br />Recently, electrodes which have a KC1 gel which needs no <br />filling_have_been made available. <br />5. On a combination glass electrode, there is a hole <br />near the tip that is filled with fiberglass or some ceramic. <br />This hole permits electrical contact with the reference <br />electrode inside the glass electrode. This fiber junction <br />has to be in the solution for the electrical circuit to be <br />completed. Solution has to flow through this hole so it <br />has to be kept free of grease and dirt. When taking the pH <br />of mucky water this can present a problem. <br />6. Always have two electrodes on hand. The only way <br />an electrode system can be checked is to see if a good elec- <br />trode system performs the way it should. As a substitute, <br />a pH meter test instrument is available from most supply <br />houses. It will serve the purpose of an extra electrode and <br />is worth the cost if a laboratory has many meters. <br />