The elemental silver precipitates out of solution, occasionally onto the inner surface of the reaction vessel, giving a characteristic "silver mirror". The carboxylate ion on acidification will give its corresponding carboxylic acid. The carboxylic acid is not directly formed in the first place as the reaction takes place under alkaline conditions. The ionic equations for the overall reaction are shown below; R refers to an alkyl group. 2[Ag(NH3)2]+ + R-CHO + H2O -> 2Ag(s) + 4NH3 + R-COOH + 2H+ Tollens' reagent can also be used to test for terminal alkynes (R-C2H). A white precipitate of the acetylide (AgC-R) is formed in this case. Another test relies on reaction of the furfural with phloroglucinol to produce a colored compound with high molar absorptivity. It also gives a positive test with hydrazines, hydrazones, α-hydroxy ketones and 1,2-dicarbonyls. Both Tollens' reagent and Fehling's reagent give positive results with formic acid. Staining In anatomic pathology, ammonical silver nitrate is used in the Fontana–Masson Stain, which is a silver stain technique used to detect melanin, argentaffin and lipofuscin in tissue sections. Melanin and the other chromaffins reduce the silver nitrate to metallic silver. In silver mirroring Tollens' reagent is also used to apply a silver mirror to glassware; for example the inside of an insulated vacuum flask. The underlying chemical process is called silver mirror reaction. The reducing agent is glucose (an aldehyde) for such applications. Clean glassware is required for a high quality mirror. To increase the speed of deposition, the glass surface may be pre-treated with tin(II) chloride stabilised in hydrochloric acid solution. For applications requiring the highest optical quality, such as in telescope mirrors, the use of tin(II) chloride is problematic, since it creates nanoscale roughness and reduces the reflectivity. Methods to produce telescope mirrors include additional additives to increase adhesion and film resilience, such as in Martin's method, which includes tartaric acid and ethanol. Safety Aged reagent can be destroyed with dilute acid to prevent the formation of the highly explosive silver nitride. See also Benedict's reagent Walden reductor (opposite use involving metallic silver) References External links Video of experimental process involving Tollens' reagent Tollens' reagent on www.wiu.edu Univ. of Minnesota Organic Chemistry Class Demo Result Silver compounds Oxidizing agents Coordination complexes Chemical tests Analytical reagents Ammine complexes