Another oxidation reaction is the basis of the "silver-mirror test". In this test, an aldehyde is treated with Tollens' reagent, which is prepared by adding a drop of sodium hydroxide solution into silver nitrate solution to give a precipitate of silver(I) oxide, and then adding just enough dilute ammonia solution to redissolve the precipitate in aqueous ammonia to produce [Ag(NH3)2]+ complex. This reagent converts aldehydes to carboxylic acids without attacking carbon–carbon double bonds. The name "silver-mirror test" arises because this reaction produces a precipitate of silver, whose presence can be used to test for the presence of an aldehyde.