GROUP II. (PHOSPHORIC ACID GROUP).

Group reagent, BaCl2.

Phosphoric, Boric, Oxalic, Hydrofluoric, Carbonic, Silicic, Sulphurous, Hyposulphurous, Arsenious, Arsenic, Iodic, and Chromic Acids.

The acids of this group are precipitated in neutral solutions by BaCl2.

GROUP III. (HYDROCHLORIC ACID GROUP).

Group reagent, AgNO3.

Hydrochloric, Hydrobromic, Hydriodic, Hydrocyanic, Hypochlorous, Nitrous, and Hydrosulphuric Acids.

The acids of this group are precipitated by AgNO3, and not by BaCl,.

GROUP IV. (NITRIC ACID GROUP).

Nitric, Chloric, and Perchloric Acids.

These acids are not precipitated by any reagent, as all their salts are soluble in water.

Reactions of the Inorganic Acids belonging to Group I.

96. Acids precipitated by BaCl, in presence of HCI.

Sulphuric Acid, Hydrofluo-silicic Acid.

SULPHURIC ACID. H2SO, c.w. 98.

1. BaCl, produces a white precipitate of BaSO, insoluble in HCl or HNO3. In very dilute solutions the precipitation is not immediate, but on standing the solution becomes clouded, and ultimately the precipitate subsides.

2. Pb(NO3)2 produces a heavy white precipitate of PbSO4, soluble in NaHO, and in boiling HCl (on allowing this solution to cool, PbCl, crystallizes out).

3. Fused on charcoal with Na,CO, in the reducing flame of the blow-pipe, a sulphide is produced. If the fused mass be moistened with HCl, the odour of H2S is at once perceptible; or if it be placed on a bright piece of silver and moistened with water, a black stain of Ag2S is produced. As the latter reaction is very delicate, care must be taken to use Na,CO, perfectly free from Na2SO4, and it must be borne in mind that other sulphur acids give the same reaction when heated with Na2CO3.

97. HYDROFLUO-SILICIC ACID. H2SiF, c.w. 144. 1. BaCl, produces a crystalline precipitate of BaSiF, insoluble in HCl.

2. KCl produces a gelatinous precipitate of K,SiF。. 3. Heated with sulphuric acid in a platinum or leaden crucible covered with a watch-glass, the latter is etched owing to the disengagement of HF.

Reactions of the Acids belonging to Group II.

98. Acids precipitated by BaCl2 in neutral solutions.

Phosphoric, Boric, Oxalic, Hydrofluoric, Carbonic, Silicic, Sulphurous, Hyposulphurous, Arsenious, Arsenic, Iodic, and Chromic Acids.

PHOSPHORIC ACID. H3PO4, c.w. 98. (Ortho-phosphoric Acid.)

1. BaCl2 produces a white precipitate of BaHPO4, readily soluble in HNO3 or HCl, but with difficulty in NH4Cl.

2. MgSO4, along with (NH)HO and NHCl, produces a white crystalline precipitate of Mg(NH4)PO1+ 6H2O, insoluble in (NH4)HO, but soluble in HCl, HNO3, and acetic acid. In dilute solutions the precipitation does not take place till after the lapse of some time, but is promoted by stirring and gentle warming.

3. AgNO, produces a yellow precipitate of Ag3PO4, soluble in HNO3, and also in (NH4)HO.

4. Lead acetate produces a white precipitate of Pb3(PO4)2, soluble in HNO3, but almost insoluble in acetic acid.

5. Fe¿Cl, in presence of excess of sodium acetate,

produces a yellowish precipitate of FePO4, soluble in HCl, and in excess of Fe,Cl, which ought therefore to be added drop by drop.*

6. Ammonium molybdate produces in solutions made acid with HNO3 a yellow coloration and ultimately a precipitate. The reaction is hastened by warming the mixture.

The following acids of phosphorus are distinguished from each other and from ortho-phosphoric acid by the following reactions :

Pyrophosphoric Acid. HP2O7, c.w. 178.

1. AgNO, produces a white precipitate of Ag1P2O7, soluble in HNO3, and in (NH)HO.

2. Albumen gives no precipitate.

Metaphosphoric Acid. HPO3, c.w. 80.

1. AgNO, produces a white gelatinous precipitate of AgPO3.

2. Albumen produces a flocculent white precipitate when added to metaphosphoric acid, and the same precipitate when added to a solution of a metaphosphate acidified with acetic acid.

3. MgSO4 + NH4Cl + (NH1)HO produces no precipitate.

* If the test be applied to an acid solution of a phosphate insoluble in water (e.g. Ca3 (PO4)2 in HCI), the free acid is first nearly neutralized with (NH4)HO, sodium acetate next added, and then FeCl6; after this the mixture is boiled. The precipitate, which is of a reddish brown colour, contains all the iron and phosphoric acid; the filtrate contains the base. The phosphoric acid can easily be separated from the iron, and obtained a soluble ammonium salt by treating the ferric phosphate with (NH4)2S.

as

99. BORIC ACID. B(HO), c.w. 62.

1. BaCl, produces a white precipitate of Ba(BO2)2, soluble in acids.

2. AgNO, produces in strong solutions a yellowish white precipitate. In dilute solutions Ag2O is precipitated.

3. H2SO4 or HCl, added to hot concentrated solutions of alkaline borates, produces on cooling a crystalline precipitate of B(HO),.

4. If alcohol containing free boric acid be kindled, it burns with a green flame, best seen on stirring the mixture. Borates may be examined in this way by first adding strong H2SO4, to liberate the B(HO)3.

5. If the solution of a borate be made distinctly acid with HCl, and turmeric paper dipped into it, the latter on gentle warming acquires a brown tint, which is turned blue by caustic soda.

100. OXALIC ACID. C2H2O4, C.W. 90.

1. BaCl, produces in neutral solutions a white precipitate of C2O4Ba, soluble in HNO3, in HCl, and in C2H2O4

2. AgNO3 produces a white precipitate of C2O4Ag2, soluble in HNO3, and in (NH)HO.

3. CaCl2 produces even in dilute solutions a white precipitate of C2O4Ca, soluble in HNO3, and in HCl, but nearly insoluble in (NH4)HO, and in acetic acid. On igniting C2O4Ca, a white residue of CaCO, is left, which effervesces on the addition of an acid.

4. Heated with strong H2SO4, effervescence takes