temperature, is a deep yellowish-green gas of a disagreeable, irritating odor, similar to that of chlorine. It dissolves in water; the dilute solution bears distillation. The hypochlorites are usually found in combination with metallic chlorides, as is the case, for instance, in chloride of lime, eau de Javelle, &c. The solutions of hypochlorites undergo alteration by boiling, the hypochlorite being resolved into chloride of the metal and chlorate of the oxide, attended, in the case of concentrated, but not in that of dilute solutions, with evolution of oxygen. If a solution of chloride of lime, &c., is mixed with hydrochloric acid or sulphuric acid, chlorine is disengaged, whilst addition of a little nitric acid leads to the liberation of hypochlorous acid. Nitrate of silver throws down from solution of chloride of lime chloride of silver; nitrate of lead produces a precipitate which from its original white changes gradually to orangered, and ultimately, owing to formation of binoxide, to brown; salts of protoxide of manganese give brown-black precipitates of hydrate of binoxide of manganese, &c. Solutions of litmus and indigo are decolorized even by the alkaline solutions of hypochlorites, but still more rapidly and completely upon addition of an acid.

THIRD GROUP OF THE INORGANIC ACIDS.

ACIDS WHICH ARE NOT PRECIPITATED BY SALTS OF BARYTA NOR BY SALTS OF SILVER: Nitric Acid, Chloric Acid.

$159.

a. NITRIC ACID (N O.).

1. Anhydrous nitric acid crystallizes in six-sided prisms. It fuses at 85.2° F., and boils at about 113° F. (Deville). The pure hydrate is a colorless, exceedingly corrosive fluid, which emits fumes in the air, exercises a rapidly destructive action upon organic substances, and colors nitrogenous matter intensely yellow. Hydrate of nitric acid containing nitrous acid

has a red color.

2. All the neutral salts of nitric acid are soluble in water; only some of the basic nitrates are insoluble in this menstruum. All nitrates without exception undergo decomposition at an intense red heat. Those with alkaline bases yield at first oxygen, and change to nitrites, which are then further resolved into oxygen and nitrogen; the others yield oxygen and nitrous or hyponitric acid.

3. If a nitrate is thrown upon red-hot charcoal, or if charcoal or some organic substance, paper for instance, is brought into contact with a nitrate in fusion, DEFLAGRATION takes place, i. e., the charcoal burns at the expense of the oxygen of the nitric acid, the combustion being attended with vivid scintillation.

4. If a mixture of a nitrate with cyanide of potassium in powder is heated on a platinum plate, a vivid DEFLAGRATION will ensue, attended with distinct ignition and detonation. Even very minute quantities of nitrates may be detected by this reaction.

5. If the solution of a nitrate is mixed with an equal volume of concentrated sulphuric acid, free from nitric and hyponitric acid, the mixture allowed to cool, and a concentrated solution of sulphate of protoxide of iron then cautiously added to it so that the fluids do not mix, the stratum, where the two fluids are in immediate contact, shows a brown or, in cases

where only a very minute quantity of nitric acid is present, a reddish color. In this process the nitric acid is decomposed by the protoxide of iron, three-fifths of its oxygen combining with the protoxide and converting a portion of it into sesquioxide, whilst the remaining nitric oxide combines with the remaining portion of the protoxide of iron, and forms with it a peculiar compound, which dissolves in water, imparting a brownish-black color to the fluid.

6. If to the solution of a nitrate some sulphuric acid is added, and as much solution of indigo in sulphuric acid as will impart a faint lightblue tint to the fluid, and the mixture is heated to boiling, the blue color changes to a faint yellowish tint, or the fluid becomes colorless. This change of color is owing to the oxidation of the indigo at the expense of the oxygen of the nitric acid which is liberated by the sulphuric acid. It must be borne in mind, however, that several other substances also cause decoloration of solution of indigo-free chlorine more particularly produces this effect.

7. If a nitrate is mixed with copper filings, and the mixture heated in a test-tube with concentrated sulphuric acid, the air in the tube acquires a yellowish-red tint, owing to the nitric oxide gas which is liberated upon the oxidation of the copper by the nitric acid, combining with the oxygen of the air to nitrous acid. The coloration may be observed most distinctly by looking lengthways through the tube.

8. If a little brucia is dissolved in concentrated sulphuric acid, and a little of a fluid containing nitric acid added to the solution, the latter immediately acquires a magnificent red color. This reaction is exceedingly characteristic.

9. Very minute quantities of nitric acid may be detected also, by fusing the substance under examination with carbonate of soda and potassa at a moderate heat, extracting the mass, after cooling, with water, filtering, adding the filtrate to a solution of iodide of potassium mixed with starch-paste, and then adding hydrochloric acid. In making the experiment, the operator has to ascertain whether the solution of iodide of potassium mixes with the hydrochloric acid without being colored blue by it, since this blue coloration would indicate the presence of iodic acid in the iodide of potassium, or of free chlorine in the hydrochloric acid.

§ 160.

b. CHLORIC ACID (Cl 0 ̧).

1. Chloric acid, in its most highly concentrated solution, is a yellow, oily fluid; its odor resembles that of nitric acid. It first reddens litmus and then bleaches it. Dilute chloric acid is colorless and inodorous.

2. All chlorates are soluble in water. When chlorates are heated to redness, the whole of their oxygen escapes and metallic chlorides remain.

3. Heated with charcoal or some organic substance, the chlorates DEFLAGRATE, and this with far greater violence than the nitrates.

4. If a mixture of a chlorate with cyanide of potassium is heated on platinum foil, DEFLAGRATION takes place, attended with strong detonation and ignition, even though the chlorate be present only in very small quantity. This experiment should be made with very minute quantities only.

5. Free chloric acid oxidizes and decolorizes indigo in the same manner as nitric acid; consequently if the solution of a chlorate is mixed with sulphuric acid and solution of indigo, and the mixture heated, the same reaction is observed as with nitric acid (see § 159, 6).

6. If the solution of a chlorate is colored light-blue with solution of indigo in sulphuric acid, a little dilute sulphuric acid added, and a solution of sulphite of soda dropped cautiously into the blue fluid, the color of the indigo disappears immediately. The cause of this equally characteristic and delicate reaction is, that the sulphurous acid deprives the chloric acid of its oxygen, thus setting free chlorine or a lower oxide of it, which then decolorizes the indigo.

7. When chlorates are treated with hydrochloric acid, the constituents of the two acids transpose, forming water, chlorine, and chlorochloric acid (2 C1 0, C1 O). Application of heat promotes the reaction. The test-tube in which the experiment is made becomes filled in this process with a greenish-yellow gas of a very disagreeable odor resembling that of chlorine; the hydrochloric acid acquires a greenish-yellow color. 8. Concentrated sulphuric acid, poured over a chlorate, converts twothirds of the metallic oxide into a sulphate and the remaining one-third into perchlorate; this conversion is attended, moreover, with liberation of chlorochloric acid, which imparts an intensely yellow tint to the sulphuric acid, and betrays its presence also by its odor and the greenish color of the evolved gas. [3 (K O, CI 0)+4 S 0,= (K O, 2 S 0,) + K O, CI 0, + (CI O,, Cl O1)]. The application of heat must be avoided in this experiment, and the quantities operated upon should be very small, since otherwise the decomposition might take place with such violence as to cause an explosion.

$161.

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Recapitulation and remarks. Of the reactions which have been suggested to effect the detection of nitric acid, those with sulphate of protoxide of iron and sulphuric acid, with copper filings and sulphuric acid, with brucia, and also those based upon the reduction of the nitrates to nitrites, give the most positive results; with regard to deflagration with charcoal, detonation with cyanide of potassium, and decoloration of solution of indigo, we have seen that these reactions belong equally to chlorates as to nitrates, and are consequently decisive only when no chloric acid is present. The presence of free nitric acid in a fluid may be detected by evaporating the fluid, in a porcelain dish on the waterbath, to dryness, having first thrown in a few quill-cuttings: yellow coloration of these indicates the presence of nitric acid (Runge). The best way to ascertain whether chloric acid is present or not, is to ignite the sample under examination, dissolve the mass, and test the solution with nitrate of silver. If a chlorate is present, this is converted into a chloride upon ignition, and nitrate of silver will now precipitate chloride of silver from the solution. However, the process is thus simple only if no chloride is present along with the chlorate. in presence of a chloride, the latter must be removed first by adding nitrate of silver to the solution as long as a precipitate continues to form, and filtering the fluid from the precipitate; the filtrate is then, after addition of pure carbonate of soda, evaporated to dryness, and the residue ignited. It is, however, generally unnecessary to pursue this circuitous

But

way, since the reactions with concentrated sulphuric acid, and with indigo and sulphurous acid, are sufficiently marked and characteristic to afford positive proof of the presence of chloric acid.

II. ORGANIC ACIDS.

First Group.

ACIDS WHICH ARE INVARIABLY PRECIPITATED BY CHLORIDE OF CALCIUM: Oxalic Acid, Tartaric Acid (Paratartaric or Racemic Acid), Citric Acid, Malic Acid.

§ 162.

a. OXALIC ACID.

For the reactions of oxalic acid I refer to § 146.

b. TARTARIC ACID (2 HO, C, H, O1).

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1. The hydrate of tartaric acid forms colorless crystals of an agreeable acid taste, which are persistent in the air, and soluble in water and in spirit of wine. Tartaric acid when heated fuses at first, and afterwards becomes carbonized, emitting during the process a very peculiar and highly characteristic odor, which resembles that of burnt sugar.

2. The tartrates with alkaline base are soluble in water, and so are those with the metallic oxides of the third and fourth groups; those of the tartrates which are insoluble in water dissolve in hydrochloric or nitric acid. The tartrates suffer decomposition when heated to redness; charcoal separates, and the same peculiar odor is emitted as attends the carbonization of free tartaric acid.

3. If to a solution of tartaric acid, or to that of a tartrate, solution of sesquioxide of iron, protoxide of manganese or alumina is added, and then ammonia or potassa, no precipitation of sesquioxide of iron, protoxide of manganese or alumina will ensue, since the double tartrates formed are not decomposed by alkalies. Tartaric acid prevents also the precipitation of several other oxides by alkalies.

4. Free tartaric acid produces with salts of potassa, and more particularly with the acetate, a difficultly soluble precipitate of BITARTRATE OF POTASSA. A similar precipitate is formed when acetate of potassa and free acetic acid are added to the solution of a neutral tartrate. The acid tartrate of potassa dissolves readily in alkalies and mineral acids; tartaric acid and acetic acid do not increase its solubility in water. The separation of the bitartrate of potassa precipitate is greatly promoted by shaking, or by rubbing the sides of the vessel with a glass rod.

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5. Chloride of calcium throws down from solutions of neutral tartrates a white precipitate of TARTRATE OF LIME (2 Ca O, C, H, O1 + 8 aq.). Presence of ammoniacal salts retards the formation of this precipitate for a more or less considerable space of time. Agitation of the fluid or friction on the sides of the vessel promotes the separation of the precipitate. The precipitate is crystalline or it invariably assumes crystalline form after some time; it dissolves in a cold not over dilute solution of potassa or soda, pretty free from carbonic acid, to a clear fluid. But upon boiling this solution, the dissolved tartrate of lime separates again in the form of a gelatinous precipitate, which redissolves upon cooling.

a

6. Lime-water produces in solutions of neutral tartrates—and also in a solution of free tartaric acid, if added to alkaline reaction-white precipitates which, flocculent at first, assume afterwards a crystalline form; so long as they remain flocculent, they are readily dissolved by tartaric acid as well as by solution of chloride of ammonium. From these solutions the tartrate of lime separates again, after the lapse of several hours, in the form of small crystals deposited upon the sides of the vessel.

7. Solution of sulphate of lime fails to produce a precipitate in a solution of tartaric acid; in solutions of neutral tartrates it produces a trifling precipitate after the lapse of some time.

8. If solution of ammonia is poured upon even a very minute quantity of tartrate of lime, a small fragment of crystallized nitrate of silver added, and the mixture slowly and gradually heated, the sides of the test-tube are covered with a bright coating of metallic silver. If instead of a crystal, solution of nitrate of silver be used, or heat be applied more rapidly, the reduced silver will separate in pulverulent form (Arthur Casselmann).

9. Acetate of lead produces white precipitates in solutions of tartaric acid and its salts. The precipitate (2 Pb O, C, H, O1) dissolves readily in nitric acid and in ammonia.

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10. Nitrate of silver does not precipitate free tartaric acid; but in solutions of neutral tartrates it produces a white precipitate of TARTRATE OF SILVER (2 Ag O, C, H, O1), which dissolves readily in nitric acid and in ammonia; upon boiling it turns black, owing to ensuing reduction of the silver to the metallic state.

11. Upon heating hydrated tartaric acid, or a tartrate, with hydrate of sulphuric acid, the sulphuric acid acquires a brown color almost simultaneously with the evolution of gas.

§ 163.

c. CITRIC ACID (3 H O, C1, H, O11).

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1. Crystallized citric acid, obtained by the cooling of its solution, has the formula, 3 HO, C, H, O, +2 aq. It crystallizes in pellucid, colorless, and inodorous crystals of an agreeable acid taste, which dissolve readily in water and in spirit of wine. Heated to 212° F., the crystallized acid loses its water of crystallization; when subjected to the action of a stronger heat, it fuses at first, and afterwards carbonizes, with evolution of pungent acid fumes, the odor of which may be readily distinguished from that emitted by tartaric acid upon carbonization.

2. The citrates with alkaline base are readily soluble in water, as well in the neutral as in the acid state; the same applies to the compounds of citric acid with such of the metallic oxides as are weak bases, sesquioxide of iron, for instance. Citrates, like tartrates, and for the same reason, prevent the precipitation of sesquioxide of iron, protoxide of manganese, alumina, &c., by alkalies.

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3. Chloride of calcium fails to produce a precipitate in solution of free citric acid, even upon boiling; but a precipitate of NEUTRAL CITRATE OF LIME (3 Ca O, C1, H, O,, +4 aq.) forms immediately upon saturating with potassa or soda the concentrated solution of citric acid, mixed with chloride of calcium in excess. The precipitate is insoluble in potassa, but it dissolves readily in solution of chloride of ammonium; upon boil