Salt bridge with agar electrolyte

The salt bridge, an agar jelly saturated with either KCl or NH4NO3, is often used to connect the two electrode compartments. This device introduces two liquid junctions, whose potentials are often opposed to one another, and the net junction potential is very small. The physical reason f or the cancellation of the two potentials is complex. The use of a jelly has some advantages in itself It prevents siphoning if the electrolyte levels differ in the two electrode compartments, and it slows the ionic diffusion very much so that the junction potentials, whatever they may be, settle down to reproducible values very quickly. 

For reactions that do not involve Ag+ or other species that react with Cl-, the salt bridge usually contains KC1 electrolyte. A typical salt bridge is prepared by heating 3 g of agar with 30 g of KC1 in 100 mL of water until a clear solution is obtained. The solution is poured into the U-tube and allowed to gel. The bridge is stored in saturated aqueous KC1. 

Agar A polysaccharide that forms a conducting gel with electrolyte solutions used in salt bridges to provide electric contact between dissimilar solutions without mixing. 

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