Under this heading are placed tests that are frequently referred to in the Pharmacopeia for the identification of official articles.[NOTEThe tests are not intended to be applicable to mixtures of substances unless so specified.]
Acetate When acetic acid or an acetate is warmed with sulfuric acid and alcohol,ethyl acetate,recognizable by its characteristic odor,is evolved.With neutral solutions of acetates,ferric chloride TSproduces a deep red color that is destroyed by the addition of mineral acids.
Aluminum With 6Nammonium hydroxide,solutions of aluminum salts yield a gelatinous,white precipitate that is insoluble in an excess of 6Nammonium hydroxide.1Nsodium hydroxide or sodium sulfide TSproduces the same precipitate,which dissolves in an excess of either of these reagents.
Ammonium Ammonium salts are decomposed by the addition of an excess of 1Nsodium hydroxide,with the evolution of ammonia,recognizable by its odor and by its alkaline effect upon moistened red litmus paper exposed to the vapor.Warming the solution accelerates the decomposition.
Antimony With hydrogen sulfide,solutions of antimony (III)compounds,strongly acidified with hydrochloric acid,yield an orange precipitate of antimony sulfide that is insoluble in 6Nammonium hydroxide,but is soluble in ammonium sulfide TS.
Barium Solutions of barium salts yield a white precipitate with 2Nsulfuric acid.This precipitate is insoluble in hydrochloric acid and in nitric acid.Barium salts impart a yellowish-green color to a nonluminous flame that appears blue when viewed through green glass.
Benzoate In neutral solutions,benzoates yield a salmon-colored precipitate with ferric chloride TS.In moderately concentrated solutions,benzoates yield a precipitate of benzoic acid upon acidification with 2Nsulfuric acid.This precipitate is readily soluble in ethyl ether.
Bicarbonate See Carbonate.
Bismuth When dissolved in a slight excess of nitric acid or hydrochloric acid,bismuth salts yield a white precipitate upon dilution with water.This precipitate is colored brown by hydrogen sulfide,and the resulting compound dissolves in a warm mixture of equal parts of nitric acid and water.
Bisulfite See Sulfite.
Borate To 1mLof a borate solution,acidified with hydrochloric acid to litmus,add 3or 4drops of iodine TSand 3or 4drops of polyvinyl alcohol solution (1in 50):an intense blue color is produced.When a borate is treated with sulfuric acid,methanol is added,and the mixture is ignited,it burns with a green-bordered flame.
Bromide Solutions of bromides,upon the addition of chlorine TS,dropwise,liberate bromine,which is dissolved by shaking with chloroform,coloring the chloroform red to reddish brown.Silver nitrate TSproduces in solutions of bromides a yellowishwhite precipitate that is insoluble in nitric acid and is slightly soluble in 6Nammonium hydroxide.
Calcium Solutions of calcium salts form insoluble oxalates when treated as follows.To a solution of the calcium salt (1in 20)add 2drops of methyl red TS,and neutralize with 6Nammonium hydroxide.Add 3Nhydrochloric acid,dropwise,until the solution is acid to the indicator.Upon the addition of ammonium oxalate TS,a white precipitate is formed.This precipitate is insoluble in 6Nacetic acid but dissolves in hydrochloric acid.Calcium salts moistened with hydrochloric acid impart a transient yellowish-red color to a nonluminous flame.
Carbonate Carbonates and bicarbonates effervesce with acids,evolving a colorless gas that,when passed into calcium hydroxide TS,produces a white precipitate immediately.Acold solution (1in 20)of a soluble carbonate is colored red by phenolphthalein TS,while a similar solution of a bicarbonate remains unchanged or is only slightly colored.
Chlorate Solutions of chlorates yield no precipitate with silver nitrate TS.The addition of sulfurous acid to this mixture produces a white precipitate that is insoluble in nitric acid,but is soluble in 6Nammonium hydroxide.Upon ignition,chlorates yield chlorides,recognizable by appropriate tests.When sulfuric acid is added to a dry chlorate,decrepitation occurs,and a greenish yellow-gas is evolved.[CautionUse only a small amount of chlorate for this test,and exercise extreme caution in performing it. ]
Chloride With silver nitrate TS,solutions of chlorides yield a white,curdy precipitate that is insoluble in nitric acid but is soluble in a slight excess of 6Nammonium hydroxide.When testing amine (including alkaloidal)hydrochlorides that do not respond to the above test,add one drop of diluted nitric acid and 0.5mLof silver nitrate TSto a solution of the substance being examined containing,unless otherwise directed in the monograph,about 2mg of chloride ion in 2mL:a white,curdy precipitate is formed.Centrifuge the mixture without delay,and decant the supernatant layer.Wash the precipitate with three 1-mLportions of nitric acid solution (1in 100),and discard the washings.Add ammonia TSdropwise to this precipitate.It dissolves readily.When a monograph specifies that an article responds to the test for dry chlorides,mix the solid to be tested with an equal weight of manganese dioxide,moisten with sulfuric acid,and gently heat the mixture:chlorine,which is recognizable by the production of a blue color with moistened starch iodide paper,is evolved.
Citrate To 15mLof pyridine add a few mg of a citrate salt,dissolved or suspended in 1mLof water,and shake.To this mixture add 5mLof acetic anhydride,and shake:a light red color is produced.
Cobalt Solutions of cobalt salts (1in 20)in 3Nhydrochloric acid yield a red precipitate when heated on a steam bath with an equal volume of a hot,freshly prepared solution of 1-nitroso-2-naphthol (1in 10)in 9Nacetic acid.Solutions of cobalt salts,when saturated with potassium chloride and treated with potassium nitrite and acetic acid,yield a yellow precipitate.
Copper Solutions of cupric compounds,acidified with hydrochloric acid,deposit a red film of metallic copper upon a bright,untarnished surface of metallic iron.An excess of 6Nammonium hydroxide,added to a solution of a cupric salt,produces first a bluish precipitate and then a deep blue-colored solution.With potassium ferrocyanide TS,solutions of cupric salts yield a reddish-brown precipitate,insoluble in diluted acids.
Hypophosphite When strongly heated,hypophosphites evolve spontaneously flammable phosphine.Hypophosphites in solution yield a white precipitate with mercuric chloride TS.This precipitate becomes gray when an excess of hypophosphite is present.Solutions of hypophosphites,acidified with sulfuric acid,and warmed with cupric sulfate TSyield a red precipitate.
Iodide Solutions of iodides,upon the addition of chlorine TS,dropwise,liberate iodine,which colors the solution yellow to red.When the solution is shaken with chloroform,the latter is colored violet.The iodine thus liberated gives a blue color with starch TS.Silver nitrate TSproduces,in solutions of iodides,a yellow,curdy precipitate that is insoluble in nitric acid and in 6Nammonium hydroxide.
Iron Ferrous and ferric compounds in solution yield a black precipitate with ammonium sulfide TS.This precipitate is dissolved by cold 3Nhydrochloric acid with the evolution of hydrogen sulfide.
Ferric Salts Acid solutions of ferric salts yield a dark blue precipitate with potassium ferrocyanide TS.With an excess of 1Nsodium hydroxide,a reddish-brown precipitate is formed.With ammonium thiocyanate TS,solutions of ferric salts produce a deep red color that is not destroyed by dilute mineral acids.
Ferrous Salts Solutions of ferrous salts yield a dark blue precipitate with potassium ferricyanide TS.This precipitate is insoluble in 3Nhydrochloric acid but is decomposed by 1Nsodium hydroxide.With 1Nsodium hydroxide,solutions of ferrous salts yield a greenishwhite precipitate,the color rapidly changing to green and then to brown when shaken.
Lactate When solutions of lactates are acidified with sulfuric acid,potassium permanganate TSis added,and the mixture is heated,acetaldehyde is evolved.This can be detected by allowing the vapor to come into contact with a filter paper that has been moistened with a freshly prepared mixture of equal volumes of 20%aqueous morpholine and sodium nitroferricyanide TS:a blue color is produced.
Lead With 2Nsulfuric acid,solutions of lead salts yield a white precipitate that is insoluble in 3Nhydrochloric or 2Nnitric acid,but is soluble in warm 1Nsodium hydroxide and in ammonium acetate TS.With potassium chromate TS,solutions of lead salts,free or nearly free from mineral acids,yield a yellow precipitate that is insoluble in 6Nacetic acid but is soluble in 1Nsodium hydroxide.
Lithium With sodium carbonate TS,moderately concentrated solutions of lithium salts,made alkaline with sodium hydroxide,yield a white precipitate on boiling.The precipitate is soluble in ammonium chloride TS.Lithium salts moistened with hydrochloric acid impart an intense crimson color to a nonluminous flame.Solutions of lithium salts are not precipitated by 2Nsulfuric acid or soluble sulfates (distinction from strontium).
Magnesium Solutions of magnesium salts in the presence of ammonium chloride yield no more than a slightly hazy precipitate when neutralized with ammonium carbonate TS,but on the subsequent addition of dibasic sodium phosphate TS,a white,crystalline precipitate,which is insoluble in 6Nammonium hydroxide,is formed.
Manganese With ammonium sulfide TS,solutions of manganous salts yield a salmon-colored precipitate that dissolves in acetic acid.
Mercury When applied to bright copper foil,solutions of mercury salts,free from an excess of nitric acid,yield a deposit that upon rubbing,becomes bright and silvery in appearance.With hydrogen sulfide,solutions of mercury compounds yield a black precipitate that is insoluble in ammonium sulfide TSand in boiling 2Nnitric acid.
Mercuric Salts Solutions of mercuric salts yield a yellow precipitate with 1Nsodium hydroxide.They yield also,in neutral solutions with potassium iodide TS,a scarlet precipitate that is very soluble in an excess of the reagent.
Mercurous Salts Mercurous compounds are decomposed by 1Nsodium hydroxide,producing a black color.With hydrochloric acid,solutions of mercurous salts yield a white precipitate that is blackened by 6Nammonium hydroxide.With potassium iodide TS,a yellow precipitate,that may become green upon standing,is formed.
Nitrate When a solution of a nitrate is mixed with an equal volume of sulfuric acid,the mixture is cooled,and a solution of ferrous sulfate is superimposed,a brown color is produced at the junction of the two liquids.When a nitrate is heated with sulfuric acid and metallic copper,brownish-red fumes are evolved.Nitrates do not decolorize acidified potassium permanganate TS(distinction from nitrites).
Nitrite When treated with dilute mineral acids or with 6Nacetic acid,nitrites evolve brownishred fumes.The solution colors starch-iodide paper blue.
Oxalate Neutral and alkaline solutions of oxalates yield a white precipitate with calcium chloride TS.This precipitate is insoluble in 6Nacetic acid but is dissolved by hydrochloric acid.Hot acidified solutions of oxalates decolorize potassium permanganate TS.
Permanganate Solutions of permanganates acidified with sulfuric acid are decolorized by hydrogen peroxide TSand by sodium bisulfite TS,in the cold,and by oxalic acid TS,in hot solution.
Peroxide Solutions of peroxides slightly acidified with sulfuric acid yield a deep blue color upon the addition of potassium dichromate TS.On shaking the mixture with an equal volume of ethyl ether and allowing the liquids to separate,the blue color is found in the ethyl ether layer.
Phosphate [NOTEWhere the monograph specifies the identification test for Phosphate,use the tests for orthophosphates,unless the instructions specify the use of the pyrophosphate tests or indicate that the product is to be ignited before performing the test.]With silver nitrate TS,neutral solutions of orthophosphates yield a yellow precipitate that is soluble in 2Nnitric acid and in 6Nammonium hydroxide.With ammonium molybdate TS,acidified solutions of orthophosphates yield a yellow precipitate that is soluble in 6Nammonium hydroxide.This precipitate may be slow to form.With silver nitrate TS,pyrophosphates obtained by ignition yield a white precipitate that is soluble in 2Nnitric acid and in 6Nammonium hydroxide.With ammonium molybdate TS,a yellow precipitate that is soluble in 6Nammonium hydroxide is formed.
Potassium Potassium compounds impart a violet color to a nonluminous flame,but the presence of small quantities of sodium masks the color unless the yellow color produced by sodium is screened out by viewing through a blue filter that blocks emission at 589nm (sodium)but is transparent to emission at 404nm (potassium).Traditionally,cobalt glass has been used,but other suitable filters are commercially available.In neutral,concentrated or moderately concentrated solutions of potassium salts (depending upon the solubility and the potassium content),sodium bitartrate TSproduces a white crystalline precipitate that is soluble in 6Nammonium hydroxide and in solutions of alkali hydroxides and carbonates.The formation of the precipitate,which is usually slow,is accelerated by stirring or rubbing the inside of the test tube with a glass rod.The addition of a small amount of glacial acetic acid or alcohol also promotes the precipitation.
Salicylate In moderately dilute solutions of salicylates,ferric chloride TSproduces a violet color.The addition of acids to moderately concentrated solutions of salicylates produces a white,crystalline precipitate of salicylic acid that melts between 158and 161.
Silver With hydrochloric acid,solutions of silver salts yield a white,curdy precipitate that is insoluble in nitric acid,but is readily soluble in 6Nammonium hydroxide.Asolution of a silver salt to which 6Nammonium hydroxide and a small quantity of formaldehyde TSare added deposits,upon warming,a mirror of metallic silver upon the sides of the container.
Sodium Unless otherwise specified in an individual monograph,prepare a solution to contain 0.1g of the sodium compound in 2mLof water.Add 2mLof 15%potassium carbonate,and heat to boiling.No precipitate is formed.Add 4mLof potassium pyroantimonate TS,and heat to boiling.Allow to cool in ice water and,if necessary,rub the inside of the test tube with a glass rod.Adense precipitate is formed.Sodium compounds impart an intense yellow color to a nonluminous flame.
Sulfate With barium chloride TS,solutions of sulfates yield a white precipitate that is insoluble in hydrochloric acid and in nitric acid.With lead acetate TS,neutral solutions of sulfates yield a white precipitate that is soluble in ammonium acetate TS.Hydrochloric acid produces no precipitate when added to solutions of sulfates (distinction from thiosulfates).
Sulfite When treated with 3Nhydrochloric acid,sulfites and bisulfites yield sulfur dioxide,which blackens filter paper moistened with mercurous nitrate TS.
Tartrate Dissolve a few mg of a tartrate salt in 2drops of sodium metaperiodate solution (1in 20).Add a drop of 1Nsulfuric acid,and after 5minutes add a few drops of sulfurous acid followed by a few drops of fuchsinsulfurous acid TS:a reddish-pink color is produced within 15minutes.
Thiocyanate With ferric chloride TS,solutions of thiocyanates yield a red color that is not destroyed by moderately concentrated mineral acids.
Thiosulfate With hydrochloric acid,solutions of thiosulfates yield a white precipitate that soon turns yellow,and sulfur dioxide,which blackens filter paper moistened with mercurous nitrate TS.The addition of ferric chloride TSto solutions of thiosulfates produces a dark violet color that quickly disappears.
Zinc In the presence of sodium acetate,solutions of zinc salts yield a white precipitate with hydrogen sulfide.This precipitate is insoluble in acetic acid,but is dissolved by 3Nhydrochloric acid.Ammonium sulfide TSproduces a similar precipitate in neutral and in alkaline solutions.With potassium ferrocyanide TS,zinc salts in solution yield a white precipitate that is insoluble in 3Nhydrochloric acid.