DETECTION OF ACIDS UNDER (a). To a portion of the solution add starch paste and one drop of a solution of N2O3 in H2SO4 Elue coloration indicates HI. Add now chlorine water till the blue colour disappears, and shake with chloroform. If this becomes reddish brown in colour, the presence of HBr is indicated. HCl is detected in the presence of the others by boiling down the solution to dryness and distilling the residue with K2Cr2O7 and H2SO4. (See 111, 3.) DETECTION OF ACIDS UNDER (6). Test separately for each acid by the methods already given. SEPARATION OF H3ASO3, H3AsO4, AND H3PO4. Acidify solution with HCl, add Na2SO3, and heat until no smell of SO2 is given off. Pass H2S through the hot solution, filter, and test for H3PO4 with ammonium molybdate: yellow precipitate indicates H3PO4. Precipitate another portion with magnesia mixture, and test both precipitate and filtrate for arsenic. TEST FOR THE REMAINING ACIDS BY THE FOLLOWING REACTIONS GIVEN UNDER EACH ACID. For HCN by test 3, 114. For H4 Fe(CN)6 by tests 3 and 4, 126. For H3 Fe(CN)6, by tests 2 and 3, 127. For H2S, by test 4, 117. *For H NO3, by tests b and c, 22. For HClO3, by tests 1 and 2, 119. For Ox and HF, by Ca Cl2 + acetic acid. Confirm Ox by test 4, 100, and HF by test 3, 101. For B (HO)3, by tests 4 and 5, 99. For Si(IO)4, by tests 2 and 4, 103. For H2CrO4, by tests 4 and 5, 110. For H2SO3 by test 3, 105, and smell of SO2 on adding HCl. For CO2 by test 2, 102. (B) Acids in Insoluble Bodies. Some idea of the nature of the compound is generally obtained by the preliminary examination (Tables A and B). If not dissolved by the * If HI be present, it must first be removed by addition of FeSO4 + CuSO4. (See 113, 2.) ordinary reagents, the substance must be fused with about four times its weight of a mixture of Na2CO3 and K2CO3. When cold, extract the fused mass with water, and filter if necessary. The filtrate contains the acid, and is neutralized with HCl or HNO3, and examined by the methods given under (a). The sulphates of barium, strontium, and calcium are decomposed by boiling with a concentrated solution of Na2CO3. Filter, and examine the filtrate for the acid. Nitric acid and aqua regia oxidize sulphides to sulphates: hence the solution of a sulphide in these acids always contains H2SO4. In such cases a separate portion of the substance must be examined for H2SO4 by boiling with HCl, diluting with water, and then testing with BaCl, 121. GROUPING OF THE ORGANIC ACIDS. GROUP I. (TARTARIC ACID Group). Group reagent, CaCl,. Tartaric Acid and Citric Acid (Oxalic Acid, see 100). Acids which are precipitated by CaCl, in the cold or on boiling. GROUP II. (BENZOIC ACID GROUP). Group reagent, Fe, Cle Benzoic and Succinic Acids. Acids which are not precipitated by CaCl2, but which give precipitates with FeCl in neutral solutions. GROUP III. Group reagent, AgNO3. Ferro-cyanic, Ferri-cyanic, Acetic and Formic Acids. Acids precipitated by AgNO, in neutral solutions, and not by CaCl2, or Fe,Cl. Acetates and Formates are only precipitated in concentrated solutions. Reactions of the Organic Acids belonging to Group I. (Tartaric Acid Group.) Acids precipitated by CaCl, in the cold or on boiling. Tartaric and Citric Acids. 122. TARTARIC ACID. CHOO. 1. CaCl2 in neutral solutions produces a white precipitate of C4H4CaO6, soluble in acids, and in ammoniacal salts. The precipitate is soluble in KHO, but is re-precipitated when the solution is boiled, and on cooling is re-dissolved. 2. KCl produces in solutions containing T in excess a white crystalline precipitate of C4H,KO, soluble in mineral acids and alkalies, insoluble in acetic acid. The precipitation is promoted by stirring, or by addition of alcohol. 3. Lime-water produces in neutral solutions a white precipitate CH4CaO, (flocculent at first, afterwards crystalline), soluble in tartaric acid and NH4Cl, but re-precipitated in crystals from these solutions after standing some time. 4. AgNO3 in neutral solutions produces a white precipitate of CH1Ag2О, soluble in HNO3 and in (NH)HO. If the solution in (NH1)HO be warmed in a test tube kept at a temperature of about 66° C. for some time, the glass becomes coated with a mirror of silver. 5. Heated with H2SO4, the mixture darkens rapidly from separation of carbon, and SO2, CO, and CO2 are evolved. 6. Heated to redness, the substance darkens in colour and gives off the characteristic odour of burnt sugar. 1. CaCl, produces no precipitate in neutral solutions in the cold, but on boiling, Ca(CHO)2 is precipitated, and is not soluble in KHO, but soluble in (NH)HO. 2. Lime-water produces no precipitate in cold neutral solutions, but on boiling, Ca,(CHO)2 is precipitated. 3. AgNO3 produces in neutral solutions a white flocculent precipitate of CH5Ag3O7, soluble in (NH1)HO: this solution does not blacken on boiling. 4. Heated with H2SO4, CO2 and CO are evolved without any darkening in colour; on continued heating, however, the mixture darkens, and SO, is evolved. 5. Heated to redness, irritating fumes are given off, readily distinguished from those given off by heating the preceding acid. Reactions of the Acids belonging to Group II. (Benzoic Acid Group.) 124. Acids precipitated by FeCl, and not by CaCl.. Benzoic and Succinic Acids. BENZOIC ACID. CH6O2. 1. FeCl produces, in neutral solutions, a buffcoloured precipitate of ferric benzoate, decomposed by |