The combination electrode consists of the following parts (see the drawing): a sensing part of electrode, a bulb made from a specific glass internal electrode, usually silver chloride electrode or calomel electrode internal solution, usually a pH=7 buffered solution of 0.1 mol/L KCl for pH electrodes or 0.1 mol/L MCl for pM electrodes when using the silver chloride electrode, a small amount of AgCl can precipitate inside the glass electrode reference electrode, usually the same type as 2 reference internal solution, usually 3.0 mol/L KCl junction with studied solution, usually made from ceramics or capillary with asbestos or quartz fiber. body of electrode, made from non-conductive glass or plastics. The bottom of apH electrode balloons out into a round thin glass bulb. The pH electrode is best thought of as a tube within a tube. The inner tube contains an unchanging 1×10−7 mol/L HCl solution. Also inside the inner tube is the cathode terminus of the reference probe. The anodic terminus wraps itself around the outside of the inner tube and ends with the same sort of reference probe as was on the inside of the inner tube. It is filled with a reference solution of KCl and has contact with the solution on the outside of the pH probe by way of a porous plug that serves as a salt bridge. Galvanic cell schematic representation This section describes the functioning of two distinct types of electrodes as one unit which combines both the glass electrode and the reference electrode into one body. It deserves some explanation. This device is essentially a galvanic cell that can be schematically represented as: Glass electrode || Reference Solution || Test Solution || Glass electrode Ag(s) | AgCl(s) | KCl(aq) || 1×10−7M H+ solution || glass membrane || Test Solution || junction || KCl(aq) | AgCl(s) | Ag(s) In this schematic representation of the galvanic cell, one will note the symmetry between the left and the right members as seen from the center of the row occupied by the "Test Solution" (the solution whose pH must be measured). In other words, the glass membrane and the ceramic junction occupies both the same relative place in each respective electrode (indicative (sensing) electrode or reference electrode). The double "pipe symbol" (||) indicates a diffusive barrier that prevents (glass membrane), or slowing down (ceramic junction), the mixing of the different solutions. By using the same electrodes on