Reaction between two reactants, which lead to the precipitation of one of the products are called metaphorical or precipitation reaction. The course of such a reaction is dependent upon the solubilities of the possible products in a particular solvent, i.e., it is solvent dependent. For example, in water barium chloride reacts with silver nitrate to yield a precipitate of silver chloride while Ba (NO₃)₂ being soluble remains in solution.
                                 H₂O
BaCI₂  +  2AsNO₃    →     Ba(NO₃)₂  +  2AgCI

On the other hand, f the reaction between (Ba(NO₃)₂ and AgCI is carried out in liquid NH₃ instead of in water, a white precipitate of BaCI₂ is obtained. We have seen
                                   liq. NH₃
2AgCI  +  Ba (NO₃)₂      →      BaCI₂ ↓ +  2AgNO₃

a reversal of the reaction on changing the solvent. Similarly, sodium hydroxide which is highly soluble in water can be precipitated in liquid ammonia and copper sulphate which is soluble in water can be precipitated form acetic acid solution.

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