THIRD GROUP OF THE INORGANIC ACIDS. ACIDS WHICH ARE NOT PRECIPITATED BY SALTS OF BARYTA NOR BY SALTS OF SILVER: Nitric Acid, Chloric Acid. (Perchloric Acid.) § 162. a. NITRIC ACID (N O). 1. ANHYDROUS NITRIC ACID crystallizes in six-sided prisms. It fuses at 85.2° F., and boils at 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 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. 6. 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 sul phate 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 purple, afterwards a brown, or, in cases where only a very minute quantity of nitric acid is present, a reddish color. If the solutions are now mixed, a clear, brownishpurple liquid is obtained. 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. A similar coloration is obtained with selenious acid; on mixing the solutions and allowing them to stand for some time, selenium separates as a red powder. (Wittstock.) 7. If some hydrochloric acid is heated to boiling in a test-tube, and one or two drops of a very dilute solution of sulphate of indigo are added, and the boiling continued, the liquid remains blue (if the hydrochloric acid be free from chlorine). If now there be added to the faint-blue liquid a nitrate, either solid or in solution, and the mixture be again boiled [and, if needful, evaporated to one-half or to a less volume], the liquid is decolorized by the destruction of the indigo-blue. This is a highly sensitive reaction. It must not be overlooked that some other bodies, especially free chlorine, have the same bleaching effect. 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 and delicate. 9. Very minute quantities of nitric acid may be detected also, by reducing, in the first place, the nitric acid to nitrous acid. This is accomplished in the wet way, by heating the solution of nitric acid or of a nitrate, for some time with zinc filings, or better with an amalgam of zinc, and then filtering off the liquid: in the dry way, by fusing the substance under examination with carbonate of soda and potassa at a moderate heat, extracting the mass, after cooling, with water, and filtering. On now adding the filtrate to a solution of iodide of potassium mixed with starch-paste, and then adding hydrochloric acid, the liquid becomes blue from the formation of iodide of starch. 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. (Compare § 161, 1.) § 163. b. CHLORIC ACID (Cl O). 1. CHLORIC ACID, in its most highly concentrated solution, is a colorless or 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 § 162, 7). 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 chiorine 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 CI O, CI 0.). 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. In case the hydrochloric acid had been tinged blue with indigo solution, the color would be at once bleached, even by a very minute quantity of a chlorate. 8. Concentrated sulphuric acid, poured over a chlorate, converts two-thirds 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 O1) + 4 SO, = 2 (K O, 2 S O2) + K O, CI 0, + (CI O, CI O3)]. 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. § 164. 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 discoloration 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 water-bath, 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.. But 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 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. To detect nitric acid in presence of a large quantity of chloric acid, the mixture is mixed with excess of carbonate of soda, evaporated to dryness if necessary, and the residue is ignited with. moderate intensity, but long enough to convert all chlorate into chloride. The residual mass is now tested for nitric (or nitrous) acid. $165. PERCHLORIC ACID (Cl O).-When anhydrous this acid is a colorless mobile liquid which explodes violently when dropped upon charcoal, and on exposure to the air, forms thick white fumes.-(RoscoE.) The hydrated acid crystallizes in needles, the concentrated aqueous solution is heavy and has an oily consistence. The dilute solution on distillation yields in the distillate first water, then the dilute, and finally the strong acid. The perchlorates are all soluble in water, most of them with ease; they are all decomposed on ignition, the alkaline perchlorates give off oxygen and alkaline chloride remains. Potassa salts produce in not too dilute solutions a white crystalline precipitate of perchlorate of potassa (KO C1 O1), which is difficultly soluble in water and insoluble in alcohol. Salts of baryta and silver are not affected. Concentrated sulphuric acid does not decompose perchloric acid in the cold and with difficulty when heated (distinction from chloric acid). Hydrochloric, aitric and sulphurous acids do not decompose an aqueous solution of perchloric acid; previously added indigo solution is, therefore, not decolorized (distinction from all other oxacids of chlorine). II. ORGANIC ACIDS. ACIDS WHICH ARE INVARIABLY PRECIPITATED BY CHLORIDE of Cal· CIUM: Oxalic Acid, Tartaric Acid (Paratartaric or Racemic Acid), Citric Acid, Malic Acid. $166. a. OXALIC ACID. For the reactions of oxalic acid I refer to § 148. b. TARTARIC ACID (2 H O, C H, O1o). 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 to 212° Fah. loses no water, at 340° Fah. it fuses and at a higher tem perature becomes carbonized, emitting during the process a very peculiar and highly characteristic odor, which resembles that of burnt sugar. The aqueous solutions of tartaric acid and of nearly all tartrates, produce right-handed rotation of a ray of polarized light. 2. The TARTRATES with alkaline base are soluble in water, and so are those with the metallic oxides of the third and fourth groups. The solution of tartrate of sesquioxide of iron, when evaporated in the water-bath to the consistence of syrup, deposits a basic salt in the form of powder. 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 in not too large quantity, 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 af a neutral tartrate. The acid tartrate of potassa dissolves |