PREPARATION OF SPECIAL ANALYTICAL REAGENTS

Paris D. N. Svoronos and Thomas J. Bruno

This listing of analytical reagents has been updated to include formulations based on more recent research, and to also include safety notes (Refs. 1–3). In addition to specific cautions, the user must always observe sound laboratory practice and housekeeping to avoid exposure and environmental contamination. When less familiar reagents are described, we include a chemical formula and a CAS Registry Number to avoid ambiguity. When a reagent calls for 95% ethanol, the azeotrope with water is specified unless noted. Additional details can be found in the references listed below.

References

1. Lide, D. R., Ed., CRC Handbook for Chemistry and Physics, 90th Edition, CRC Press, Boca Raton, FL, 2010.
2. Bruno, T. J., and Svoronos, P. D. N., CRC Handbook of Basic Tables for Chemical Analysis – Data-Driven Methods and Interpretation, Fourth Edition, CRC Press/Taylor & Francis, Boca Raton, FL, 2021. [https://doi.org/10.1201/b22281]
3. Svoronos, P. D. N., Sarlo, E., and Kulawiec, R., Organic Chemistry Laboratory Manual, WCB McGraw-Hill, New York, 1996.

• Aluminon (qualitative test for aluminum). Aluminon is the name for the triammonium salt of aurintricarboxylic acid (5-[(3-carboxy-4-hydroxyphenyl)(3-carboxy-4-oxo-2,5-cyclohexadienylidene)methyl]-2-hydroxybenzoic acid triammonium salt, C₂₂H₂₃N₃O₉, CAS No. 569-58-4). Dissolve 1 g of the salt in 1 L of distilled water. Shake the solution well to ensure thorough mixing.
• Bang’s reagent (for glucose estimation). Dissolve (in the exact order) 100 g of potassium carbonate, 66 g of potassium chloride and 160 g of anhydrous potassium bicarbonate in approximately 700 mL of distilled water at 30 °C. Add (while stirring) 4.4 g of copper (II) sulfate and dilute to 1 L with distilled water after all CO₂ has been released. This solution should be shaken and saved in an air-tight flask. After 24 hours, 300 mL of it are diluted to 1 L with a saturated aqueous potassium chloride solution, shaken gently and used after 24 hours. 50 mL of this solution is equivalent to 10 mg glucose.
• Barfoed’s reagent (test for glucose). See Cupric acetate.
• Baudisch’s reagent. See Cupferron.
• Benedict’s solution (qualitative reagent for glucose). Dissolve 173 g of sodium citrate and 100 g of sodium carbonate in 800 mL of distilled water. Filter, if necessary, and dilute to 850 mL with distilled water. Dissolve 17.3 g of copper (II) sulfate pentahydrate in 100 mL of distilled water. Pour the latter solution, with constant stirring, into the carbonate-citrate solution and dilute to 1 L with distilled water.
• Benzidine hydrochloride solution (for sulfate determination). Prepare a paste of 8 g of benzidine hydrochloride (C₁₂H₈(NH₃)₂·2HCl) and 20 mL of distilled water, add 20 mL of 20% (mass/mass) HCl and dilute to 1 L with distilled water. Each mL of this solution is equivalent to 0.00357 g of H₂SO₄. Note that the reagent is often called benzidine dihydrochloride.
• Bertrand’s reagent (glucose estimation). Consists of the following solutions:
  1. Dissolve 200 g of Rochelle salt (potassium sodium tartrate, NaKC₄H₄O₆ ) and 150 g of NaOH in sufficient distilled water to make 1.0 L of solution.
  2. Dissolve 40 g of copper (II) sulfate pentahydrate in sufficient distilled water to a total of 1.0 L of solution.
  3. Dissolve 50 g of iron (III) sulfate and 200 g of H₂SO₄ (sp. gr. 1.84) in sufficient distilled water to a total of 1.0 L of solution.
  4. Dissolve 5 g of potassium permanganate in sufficient distilled water to a total of 1.0 L solution.
• Bial’s reagent (for pentose). Dissolve 1 g of orcinol (5-methyl-1,3-benzenediol, C₇H₈O₂, CAS No. 504-15-4) in 500 mL of 30% (mass/mass) HCl to which 30 drops of a 10% aqueous solution of iron (III) chloride have been added.
• Boutron — Boudet soap solution: Consists of the following solutions:
  1. Dissolve 100 g of pure castile soap (olive oil based) in about 2.5 L of 56% (vol/vol) aqueous ethanol.
  2. Dissolve 0.59 g of barium nitrate in 1.0 L of water. Adjust the castile soap solution (1) so that 2.4 mL of it will produce a permanent lather with 40 mL of solution (2). When adjusted, 2.4 mL of this soap solution is equivalent to 220 parts per million of hardness (as calcium carbonate) for a 40 mL sample. See also Soap solution.
• Brucke’s reagent (protein precipitation). See Potassium iodide mercuric iodide.
• Cobaltic cyanide paper (Rinnmann’s test for zinc detection). Dissolve 4 g of potassium cobalt (III) hexacyanide (K₃Co(CN)₆) and 1 g of potassium chlorate in 100 mL of water. Soak filter paper in solution and dry at 100 °C. Apply a drop of the zinc solution and heat in an evaporating dish. A green disk on the filter paper is obtained if zinc is present.
• Congo red. Dissolve 0.5 g of Congo red (3,3’-([1,1’-biphenyl]-4,4’-diyl)bis(4-aminonaphthalene-1-sulfonic acid, C₃₂H₂₂N₆Na₂O₆S₂, CAS No. 573-58-0) in 90 mL of distilled water and 10 mL of ethanol.
• Cupferron (Baudisch’s reagent for iron analysis). Dissolve 6 g of Cupferron, the ammonium salt of N-hydroxy-N-nitrosoaniline (NH₄[C₆H₅N(O)NO]) in 100 mL of distilled water. The reagent is good only for one week and must be kept in the dark.
• Cupric acetate (Barfoed’s reagent for reducing monosaccharides). Dissolve 66 g of copper (II) acetate and 10 mL of glacial acetic acid in water and dilute to 1.0 L.
• Cupric oxide, ammoniacal; Schweitzer’s reagent (dissolves cotton, linen, and silk, but not wool). Dissolve 5 g of cupric sulfate in 100 mL of boiling water and add sodium hydroxide until precipitation is complete. Wash the precipitate well and dissolve it in a minimal quantity of ammonium hydroxide. Bubble a slow stream of air through 300 mL of concentrated ammonium hydroxide solution containing 50 g of fine copper turnings. Continue stirring for 1 hour.
• Cupric sulfate in glycerin-potassium hydroxide (reagent for silk). Dissolve 10 g of copper (II) sulfate pentahydrate in 100 mL of water and add 5 g of glycerol. Add 6N KOH solution slowly until a deep blue solution is obtained.
• Cupron (precipitates copper). Dissolve 5 g of benzoinoxime in 100 mL 95% ethanol.
• Cuprous chloride, acidic (reagent for CO in gas analysis).
  1. Cover the bottom of a 2 L flask with a layer of copper (II) oxide about 1.5 cm deep, suspend a coil of copper wire so as to reach from the bottom to the top of the solution, and fill the flask with hydrochloric acid 20% (vol/vol) HCl(aq) with continuous stirring. When the solution becomes nearly colorless, transfer to reagent bottles, which should also contain copper wire. The stock bottle may be refilled with dilute (6N) HCl until either the cupric oxide or the copper wire is used up. Copper (II) sulfate may be substituted for copper oxide in the above procedure.
  2. Dissolve 340 g of copper (II) chloride dihydrate in 600 mL of concentrated HCl and reduce the cupric chloride by adding 190 mL of a saturated solution of stannous chloride or until the solution is colorless. The stannous chloride is prepared by treating 300 g of metallic tin in a 500 mL flask with concentrated HCl until no more tin is dissolved.
  3. (Winkler method). Add a mixture of 86 g of copper (II) chloride and 17 g of finely divided metallic copper, prepared by the reduction of 8 g to 12 g of cupper (II) oxide with hydrogen gas, to a solution of HCl, made by diluting 650 mL of concentrated HCl with 325 mL of distilled water. After the mixture has been added slowly and with frequent stirring, a spiral of copper wire is suspended in the bottle, reaching all the way to the bottom. The solution is ready to use when the solution becomes colorless.
• Cuprous chloride, ammoniacal (reagent for CO in gas analysis).
  1. The acid solution of copper (II) chloride as prepared above is neutralized with 6N ammonium hydroxide until the ammonia odor persists. An excess of metallic copper must be kept in the solution.
  2. Pour 800 mL of acidic copper (II) chloride, prepared by the Winkler method, into approximately 4 L of water. Transfer the precipitate to a 250 mL graduated cylinder. After several hours, siphon off the liquid above the 50 mL mark and refill with 7.5% ammonium hydroxide solution which may be prepared by diluting 50 mL of concentrated ammonium hydroxide with 150 mL of distilled water. The solution, which should have a faint odor of ammonia should be well stirred and allowed to stand for several hours.
  Note: Proper precautions must be taken for the safe handling of gaseous samples that contain CO.
• Dichlorofluorescein indicator. Dissolve 1 g dichlorofluorescein (C₂₀H₁₀Cl₂O₅, CAS No. 76-54-0) in 1 L 70% (vol/vol) ethanol or 1 g of the sodium salt in 1 L of distilled water.
• Dimethyglyoxime, 0.01 N. Dissolve 0.6 g of dimethylglyoxime (2,3-butanedione oxime) in 500 mL of 95% ethanol. This is an especially sensitive test for nickel (II) and produces a very characteristic crimson color.
• Diphenylamine (reagent for rayon). Dissolve 0.2 g diphenylamine in 100 mL of concentrated sulfuric acid.
• Diphenylamine sulfonate (for titration of iron with K₂Cr₂O₇). Dissolve 0.32 g of the barium salt of diphenylamine sulfonic acid in 100 mL of distilled water, add 0.5 g of sodium sulfate and filter off the precipitated barium sulfate.
• Diphenylcarbazide. Dissolve 0.2 g of diphenylcarbazide[(C₆H₅NHNH)₂CO] in 10 mL of glacial acetic acid and dilute to 100 mL with 95% ethanol.
• 2,4-Dinitrophenylhydrazine (2,4-DNP) reagent. Dissolve 3 g of 2,4-dinitrophenylhydrazine in 15 mL to 20 mL of concentrated sulfuric acid. Add this solution with stirring to a solution of 10 mL distilled water in 70 mL of 95% hydrous ethanol. Use the filtrate to test for the presence of aldehydes and ketones as follows: To 2 mL of the solution add 10 drops of the unknown. A precipitate (which may be recrystallized from 95% hydrous ethanol) is indicative of a positive test and its melting point can be matched to the corresponding melting points of various aldehydes and ketones.
• Esbach’s reagent (estimation of protein). Dissolve 10 g of picric acid and 20 g of citric acid in sufficient distilled water to make a 1.0 L of solution.
• Eschka’s compound. Two parts of calcinated (“light”) magnesia are thoroughly mixed with 1 part of anhydrous sodium carbonate.
• Fehling’s solution (reagent for reducing sugars).
  1. Copper (II) sulfate solution: Dissolve 34.66 g of copper (II) sulfate pentahydrate in distilled water and dilute to 500 mL.
  2. Alkaline tartrate solution: Dissolve 173 g of potassium sodium tartrate (Rochelle salt, KNaC₄H₄O₆·4H₂O) and 50 g of NaOH in distilled water, cool and dilute to 500 mL. Mix equal volumes of solutions (1) and (2) just before using.
• Ferric-alum indicator. Dissolve 140 g of iron (III) ammonium sulfate crystals in 400 mL of hot distilled water. Cool, filter, and add enough 6N nitric acid until the 500 mL mark.
• Folin’s mixture (for uric acid). To 650 mL of distilled water add 500 g of ammonium sulfate, 5 g of uranium (VI) acetate, and 6 g of glacial acetic acid and then dilute to 1.0 L with distilled water.
• Formaldehyde — sulfuric acid (Marquis’ reagent for alkaloids). Add 100 mL of concentrated sulfuric acid to 5 mL of 37% (mass/mass) aqueous formaldehyde solution.
• Froehde’s reagent. See Sulfomolybdic acid.
• Fuchsin (reagent for linen). Dissolve 1 g of fuchsin (an aniline dye) in 100 mL of ethanol.
• Fuchsin — sulfurous acid (Schiff’s reagent for aldehydes). Dissolve 0.5 g of fuchsin and 9 g of sodium bisulfite in 500 mL of distilled water,and add 10 mL of concentrated HCl. Keep in well-stoppered bottles and protect from light. The fuchsin used to make the Schiff reagent should incorporate a high content of pararosanilin.
• Gunzberg’s reagent (detection of HCl in gastric juice). Dissolve 4 g of phloroglucinol (1,3,5-benzenetriol, C₆H₃(OH)₃) and 2 g of vanillin (C₈H₈O₃) in 100 mL of absolute ethanol.
• Hager’s reagent. See Picric acid.
• Hanus solution (for iodine number). Dissolve 13.2 g of resublimed iodine in 1 L of glacial acetic acid, which should pass the dichromate test for reducible matter. Add sufficient bromine to double the halogen content, as determined by titration (approximately 3 mL). The iodine may be dissolved by heating, but the solution should be cold when the bromine is added.
• Hopkins-Cole reagent (test for presence of the indole ring in the tryptophan moiety of a protein or peptide). Add 5 mL cold water to 10 g of magnesium in a conical flask and add 250 mL of a cold saturated aqueous oxalic acid solution with vigorous stirring. Filter, add 25 mL of glacial acetic acid and dilute with distilled water to the 1.0 L mark. Place 10 drops of the saturated protein or peptide solution in a test tube, add 10 drops of concentrated nitric acid and heat in a water bath for 3 minutes. Allow the mixture to cool and add 4 mL 6N NaOH. A positive test is confirmed by the formation of a yellow color.
• Iodine, tincture of. To 50 mL of distilled water add 70 g of iodine and 50 g of potassium iodide. Dilute to 1 L with absolute ethanol.
• Iodo-potassium iodide (Wagner’s reagent for alkaloids). Dissolve 2 g of iodine and 6 g of KI in 100 mL of distilled water.
• Jones reagent (test is positive for 1^o and 2^o alcohols, aldehydes, mercaptans, sulfides, and sulfoxides). To 1 mL of 5% (mass/mass) sodium (or potassium) dichromate add 10 drops of the unknown compound. The formation of a green color (sometimes appearing as brown due to the mixture of the green chromium (III) and the unreacted orange chromium (VI) colors) indicates a positive test.
• Litmus (indicator). Extract litmus powder three times with boiling alcohol (ethanol or isopropanol), each treatment lasting for an hour. Discard the alcoholic extract. Treat the residue with an equal mass of cold distilled water and filter; then add five times its weight of boiling distilled water. Cool, filter, and combine all aqueous extracts.
• Magnesia mixture (reagent for phosphates and arsenates). Dissolve 50 g of magnesium chloride (MgCl₂·6H₂O) and 100 g of ammonium chloride (NH₄Cl) in 500 mL of distilled water, add a slight excess of NH₄OH, and allow to stand overnight. Filter, make the solution just acidic with HCl, and dilute with distilled water to 1 L. Let stand for several days and separate the precipitated solid by decanting. The decantate should be used just prior to testing; otherwise, if stored for any period of time it becomes turbid.
• Magnesium uranyl acetate. Dissolve 100 g of uranyl (VI) acetate dehydrate (UO₂(C₂H₃O₂)₂·2H₂O) in 60 mL of glacial acetic acid and dilute to 500 mL with distilled water. Dissolve 330 g magnesium acetate tetrahydrate (Mg(C₂H₃O₂)₂·4H₂O) in 60 mL of glacial acetic acid and dilute to 200 mL. Heat both solutions to boiling until clear; pour the magnesium acetate solution into the uranyl acetate solution, cool and dilute with distilled water to 1 L. Let stand overnight and filter if necessary.
• Marme’s reagent. See Potassium-cadmium iodide.
• Marquis’ reagent. See Formaldehyde-sulfuric acid.
• Mayer’s reagent (white precipitate with most alkaloids in slightly acid solutions). Dissolve 1.358 g of mercury (II) chloride in 60 mL of distilled water and pour into a solution of 5 g of potassium iodide in 10 mL of distilled water. Add sufficient distilled water to a final volume of 100 mL.
• Methyl orange indicator. Dissolve 1 g of methyl orange in 1 L of distilled water. Filter, if necessary.
• Methyl orange, modified. Dissolve 2 g of methyl orange and 2.8 g of xylene cyanole FF (C₂₅H₂₇N₂NaO₆S₂, CAS No: 2650-17-1) in 1 L of 50% (vol/vol) ethanol.
• Methyl red indicator. Dissolve 1 g of methyl red in 600 mL of ethanol and dilute with 400 mL of distilled water.
• Methyl red, modified. Dissolve 0.50 g of methyl red and 1.25 g of xylene cyanole FF (C₂₅H₂₇N₂NaO₆S₂) in 1 L of 90% (vol/vol) ethanol. Alternatively dissolve 1.25 g of methyl red and 0.825 g of methylene blue in 1 L of 90% (vol/vol) ethanol.
• Millon’s reagent (for albumins and phenols). Dissolve 1 part of mercury in 1 part of cold fuming nitric acid. Dilute with twice the volume of distilled water and decant the clear solution after several hours. All appropriate precautions must be observed when handling mercury.
• Molisch’s reagent. See 1-Naphthol.
• 1-Naphthol (Molisch’s reagent for wool). Dissolve 15 g of 1-naphthol in 100 mL of 95% (vol/vol) ethanol or chloroform.
• Nessler’s reagent (for ammonia). Dissolve 50 g of potassium iodide in the smallest possible quantity of cold distilled water (50 mL). Add a saturated solution of mercury (II) chloride (about 22 g in 350 mL of distilled water will be needed) until an excess is indicated by the formation of a precipitate. Then add 200 mL of 5 N NaOH and dilute to 1 L with distilled water. Allow to settle and draw off the clear liquid.
• Nickel oxide, ammoniacal (reagent for silk). Dissolve 5 g of nickel (II) sulfate in 100 mL of distilled water and add 6N NaOH solution until nickel hydroxide is completely precipitated. Wash the precipitate well and dissolve in 25 mL of concentrated ammonium hydroxide and 25 mL of distilled water.
• Nitron (detection of the nitrate radical). Dissolve 10 g of nitron (1,4-diphenyl-3-(phenylamino)-1,2,4-triazolium hydroxide, C₂₀H₁₈N₄O) in 5 mL of glacial acetic acid and 95 mL of distilled water. The solution may be filtered with slight suction through an Alundum thimble crucible and kept in a dark bottle.
• 1-Nitroso-2-naphthol. Make a saturated solution 1-nitroso-2-naphthol in 50% (vol/vol) aqueous acetic acid. The reagent should be used as soon as it is prepared.
• Nylander’s solution (carbohydrates). Dissolve 20 g of bismuth subnitrate (Bi₅O(OH)₉(NO₃)₄) and 40 g of Rochelle salt (potassium sodium tartrate, KNaC₄H₄O₆·4H₂O) in 1 L of 8% (mass/mass) aqueous NaOH solution. Cool and filter.
• Obermayer’s reagent (for indoxyl in urine). Dissolve 4 g of iron (III) chloride in 1 L of aqueous (vol/vol) 40% HCl.
• Oxine. Dissolve 14 g of 8-hydroxyquinoline (C₉H₇NO) in 30 mL of glacial acetic acid. Warm slightly, if necessary, to dissolve. Dilute to 1 L with distilled water.
• Oxygen absorbent. Dissolve 300 g of ammonium chloride in 1 L distilled water and add 1 L of concentrated ammonium hydroxide solution. Shake the solution thoroughly. For use as an oxygen absorbent, the gas to be tested is passed through a bottle that is half-full of copper turnings filled nearly to the top with this ammonium chloride — ammonium hydroxide solution.
• Pasteur’s salt solution. To 1 L of distilled water add 2.5 g of potassium phosphate, 0.25 g of calcium phosphate, 0.25 g of magnesium sulfate, and 12.00 g of ammonium tartrate.
• Pavy’s solution (glucose reagent). To 120 mL of Fehling’s solution, add 300 mL of 6N ammonium hydroxide (sp. gr. 0.88) and dilute to 1 L with distilled water.
• Phenanthroline ferrous ion indicator. Dissolve 1.485 g of 1,10-phenanthroline monohydrate (C₁₂H₈N₂·H₂O) in 100 mL of 0.025 M aqueous iron (II) sulfate solution.
• Phenolphthalein. Dissolve 1 g of phenolphthalein in 50 mL of ethanol and add 50 mL of distilled water.
• Phenolsulfonic acid (determination of nitrogen as nitrate). Dissolve 25 g of phenol in 150 mL of concentrated H₂SO₄, add 75 mL of fuming sulfuric acid (approximately 15% SO₃), stir well and heat for 2 hours at 100 °C.
• Phloroglucinol solution (pentosans). Make a 3% phloroglucinol (1,3,5-benzenetriol) solution in alcohol. Store in a dark bottle.
• Phosphomolybdic acid (Sonnenschein’s reagent for alkaloids).
  1. Prepare ammonium phosphomolybdate and after washing with distilled water, boil with nitric acid to expel all ammonia. Evaporate to dryness and dissolve in 2 M HNO₃.
  2. Dissolve ammonium molybdate in HNO₃ and treat with phosphoric acid. Filter, wash the precipitate, and boil with aqua regia (a mixture of concentrated nitric acid and concentrated hydrochloric acid, 1:3 vol/vol) until the ammonium salt is decomposed. Evaporate to dryness. The residue is dissolved in 10% (vol/vol) HNO₃. The solution constitutes Sonnenschein’s reagent.
• Phosphoric acid — sulfuric acid mixture. Dilute 150 mL of concentrated sulfuric acid and 100 mL of concentrated phosphoric acid with distilled water to a final volume of 1 L.
• Phosphotungstic acid (Scheibler’s reagent for alkaloids).
  1. Dissolve 20 g of sodium tungstate and 15 g of sodium phosphate in 100 mL of distilled water slightly acidified with dilute nitric acid.
  2. The reagent is a 10% (mass/mass) solution of phosphotungstic acid in distilled water. The phosphotungstic acid is prepared by evaporating a mixture of 10 g of sodium tungstate dissolved in 5 g of phosphoric acid (sp. gr. 1.13) and enough boiling water to a complete solution. Crystals of phosphotungstic acid will separate.
• Picric acid (Hager’s reagent for alkaloids, wool, and silk). Dissolve 1 g of picric acid in 100 mL of distilled water.
• Potassium antimonate (reagent for sodium). Boil 22 g of potassium antimonate with 1 L of distilled water until nearly all of the salt has dissolved, cool quickly, and add 35 mL of 10% (mass/mass) potassium hydroxide. Filter after standing overnight.
• Potassium-cadmium iodide (Marme’s reagent for alkaloids). Add 2 g of cadmium (II) chloride to a boiling solution of 4 g of potassium iodide in 12 mL of distilled water, and then mix with 12 mL of saturated aqueous potassium iodide solution.
• Potassium hydroxide (for CO₂ absorption). Dissolve 360 g of potassium hydroxide in distilled water and dilute to 1 L.
• Potassium iodide — mercuric iodide (Brucke’s reagent for proteins). Dissolve 50 g of potassium iodide in 500 mL of distilled water and saturate with mercury (II) iodide (about 120 g). Dilute to 1 L with distilled water.
• Potassium pyrogallate (for oxygen absorption). For mixtures of gases containing less than 28% (mass/mass) oxygen, add 100 mL of potassium hydroxide solution (50 g of KOH to 100 mL of distilled water) to 5 g of pyrogallol. For mixtures containing more than 28% (mass/mass) oxygen, the KOH solution should contain instead 120 g of KOH in 100 mL of distilled water.
• Pyrogallol, alkaline. The reagent is a mixture of two solutions
  1. Dissolve 75 g of pyrogallic acid in 75 mL of distilled water.
  2. Dissolve 500 g of KOH in 250 mL distilled water. When cooled, adjust the solution with distilled water until the concentration is 50% (vol/vol).
  3. For use, add 270 mL of solution (2) to 30 mL of solution (1).
• Rosolic acid (indicator). Dissolve 1 g of rosolic acid (C₁₉H₁₄O₃) in 10 mL of ethanol and add 100 mL of distilled water.
• Sakaguchi reagent (for the presence of arginine in proteins or peptides). To 10 drops of the saturated protein or peptide solution, add 5 drops of 6 N NaOH followed by 5 drops of 0.05% (mass/mass) ethanolic 1-naphthol solution and 10 drops of 0.5% aqueous sodium hypochlorite. A positive test is indicated by the formation of a red color that fades away upon standing.
• Scheibler’s reagent. See Phosphotungstic acid.
• Schiff’s reagent. See Fuchsin-sulfurous acid.
• Schweitzer’s reagent. See Cupric oxide, ammoniacal.
• Soap solution (reagent for hardness in water). Dissolve 100 g of dry castile soap in 1 L of 80% (vol/vol) ethanol (4 parts ethanol to 1 part distilled water). Allow to stand for several days and dilute with 70% ethanol until 6.4 mL of this solution produces a permanent lather with 20 mL of standardized calcium solution. The latter solution is made by dissolving 0.2 g of calcium carbonate in a small amount of dilute HCl, evaporating to dryness and then dissolving the precipitate with distilled water to a final volume of 1 L.
• Sodium bismuthate (for the oxidation of manganese). Heat 20 parts of sodium hydroxide nearly to redness in an iron or nickel crucible and add slowly 10 parts of basic bismuth (III) nitrate which has been previously dried. Add 2 parts of sodium peroxide and pour the brownish-yellow fused mass onto an iron plate to cool. When cooled, break up in a mortar, extract with distilled water, and collect on an asbestos filter.
• Sodium hydroxide (for CO₂ absorption). Dissolve 330 g of sodium hydroxide in distilled water and dilute to 1 L.
• Sodium nitroprusside (reagent for hydrogen sulfide and wool). Use a freshly prepared solution of 1 g of sodium nitroferricyanide in 10 mL of distilled water.
• Sodium oxalate (primary standard). Dissolve 30 g of the commercial salt of sodium oxalate in 1 L of distilled water, make slightly alkaline with sodium hydroxide, and let stand until clear. Filter and evaporate the filtrate to 100 mL. Cool and filter. Pulverize the residue and wash it several times with small volumes of distilled water. The procedure is repeated until the mother liquor is sulfate-free and is neutral to phenolphthalein.
• Sodium plumbite (reagent for wool). Dissolve 5 g of sodium hydroxide in 100 mL distilled water. Add 5 g of litharge (lead (II) oxide) and boil until dissolved.
• Sodium polysulfide. Dissolve 480 g of sodium sulfide nonahydrate in 500 mL of distilled water, add 40 g of NaOH and 18 g of sulfur. Stir thoroughly and dilute to 1 L with distilled water.
• Sonnenschein’s reagent. See Phosphomolybdic acid.
• Starch solution.
  1. Make a paste with 2 g of soluble starch and 0.01 g of mercury (II) iodide with a small amount of distilled water. Add the mixture slowly to 1 L of boiling distilled water and boil further for a few minutes. Keep in a glass stoppered bottle. If other than soluble starch is used, the solution will not be clear on boiling; it should then be allowed to stand, and the clear liquid decanted.
  2. A solution of starch that keeps stable indefinitely is made as follows: Mix 500 mL of aqueous saturated NaCl solution (filtered), 80 mL of glacial acetic acid, 20 mL of distilled water and 3 g of starch. Bring slowly to a boil and further heat for 2 minutes.
  3. Make a paste with 1 g of soluble starch and 5 mg of mercury (II) iodide using as little cold distilled water as possible. Then pour about 200 mL of boiling distilled water on the paste and stir immediately. This will give a clear solution if the paste is prepared correctly and the water is actually boiling. Cool and add 4 g of potassium iodide. Starch solution decomposes on standing due to bacterial action, but this solution will be stable if stored under a layer of toluene.
• Stoke’s reagent. Dissolve 30 g of iron (II) sulfate and 20 g of tartaric acid in distilled water and dilute to 1 L. Just before using, add concentrated ammonium hydroxide until the precipitate that is initially formed is redissolved.
• Sulfanilic acid (reagent for nitrites). Dissolve 0.5 g of sulfanilic acid in a mixture of 15 mL of glacial acetic acid and 135 mL of recently boiled distilled water.
• Sulfomolybdic acid (Froehde’s reagent for alkaloids and glucosides). Dissolve 10 g of molybdic acid or sodium molybdate in 100 mL of concentrated sulfuric acid.
• Tannic acid (reagent for albumin, alkaloids, and gelatin). Dissolve 10 g of tannic acid in 10 mL of ethanol and dilute with distilled water to 100 mL.
• Titration mixture (residual chlorine in water analysis). Prepare 1 L of dilute HCl (100 mL of HCl (sp. gr. 1.19) in sufficient distilled water to make 1 L). Dissolve 1 g of o-tolidine (3,3’-dimethylbenzidine, CAS No. 119-93-7) in 100 mL dilute hydrochloride, stir well and dilute to 1 L using dilute HCl solution.
• Tollen’s reagent (confirming the presence of aldehydes). 5 drops of 5% NaOH is added to 2 mL 10% aqueous silver nitrate in a test tube. The insoluble silver (I) oxide dissolved by the drop wise addition of 10% aqueous ammonia (ammonium hydroxide) yields a clear solution. Excess ammonium hydroxide should be avoided as it may give false-positive result. Approximately 10 drops of the aldehyde will yield a silver mirror coating on the test tube inner wall, especially if the mixture is warmed up to 50 °C.
• Trinitrophenol solution. See Picric acid.
• Turmeric tincture (reagent for borates). Digest ground turmeric root with several quantities of distilled water which are discarded. Dry the residue and digest it several days with six times its weight of ethanol. Filter.
• Uffelmann’s reagent (turns yellow in presence of lactic acid). To a 2% solution of pure phenol in distilled water, add an aqueous solution of iron (III) chloride until the phenol solution becomes violet in color.
• Wagner’s reagent. See Iodo-potassium iodide.
• Wagner’s solution (used in phosphate rock analysis to prevent precipitation of iron and aluminum). Dissolve 25 g of citric acid and 1 g of salicylic acid in distilled water and dilute to 1 L. Use 50 mL of the reagent.
• Wij’s iodine monochloride solution (for iodine number). Dissolve 13 g of resublimed iodine in 1 L of glacial acetic acid that will pass the dichromate test for reducible matter. Set aside 25 mL of this solution. Bubble into the remainder of the solution dry chlorine gas (dried and washed by passing through concentrated sulfuric acid) until the characteristic color of free iodine has been dissipated. Add the 25 mL of the iodine solution that was set aside, until all free chlorine has been dissipated. A slight excess of iodine does little or no harm, but an excess of chlorine must be avoided. Preserve in well stoppered, amber-colored bottles. Avoid the use of solutions that have been stored for more than 30 days.
• Wij’s special solution (for iodine number). To 200 mL of glacial acetic acid that will pass the dichromate test for reducible matter, add 12 g of dichloramine T (N,N-dichloro-4-methylbenzenesulfonamide, CAS No. 473-34-7), and 16.6 g of dry potassium crystals (in small quantities with continual shaking until all the potassium iodide has dissolved). Dilute to 1 L with the same quality of acetic acid used above and preserve in a dark-colored bottle.
• Zimmermann-Reinhardt reagent (determination of iron). Dissolve 70 g of manganese (II) sulfate tetrahydrate in 500 mL of water, add slowly 125 mL of concentrated sulfuric acid and 125 mL of 85% phosphoric acid, and dilute to 1 L with water.
• Zinc chloride solution, basic (reagent for silk). Dissolve 1000 g of zinc chloride in 850 mL of distilled water and add 40 g of zinc oxide. Heat until complete dissolving is complete.
• Zinc uranyl acetate (reagent for sodium). Dissolve 10 g of UO₂(C₂H₃O₂)₂·2H₂O in 6 g of 30% acetic acid, heat, if necessary, and dilute to 50 mL. Dissolve 30 g of zinc acetate dehydrate in 3 g of 30% acetic acid and dilute to 50 mL. Mix the two solutions, add 50 mg of sodium chloride, allow to stand overnight and filter. Use distilled water in all dilutions.