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, O10). 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. 8 10 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, O,,) dissolves readily in nitric acid and in ammonia. 4 10 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, O), 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). 12 11 12 5 1. Crystallized citric acid, obtained by the cooling of its solution, has the formula, 3 HO, C12 H, O1, + 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. 12 5 11 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, C12 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 ing this chloride of ammonium solution, neutral citrate of lime of the same composition separates again in the form of a white crystalline precipitate, which, however, is now no longer soluble in chloride of ammonium. If a solution of citric acid mixed with chloride of calcium is saturated with ammonia, a precipitate will form in the cold only after many hours' standing; but upon boiling the clear fluid, neutral citrate of lime of the properties just stated will suddenly precipitate. When citrate of lime is heated with ammonia and nitrate of silver, no reduction of the latter salt ensues. 4. Lime-water produces no precipitate in cold solutions of citric acid or of citrates. But upon heating the solution to boiling, with a tolerable excess of hot prepared lime-water, a white precipitate of CITRATE OF LIME is formed, of which the greater portion redissolves upon cooling. 5. Acetate of lead, when added in excess to a solution of citric acid, produces a white precipitate of CITRATE OF LEAD (3 Pb O, C1, H ̧ 01), which, after washing, dissolves readily in ammonia. 5 6. Nitrate of silver produces in solutions of neutral citrates of the alkalies a white, flocculent precipitate of CITRATE OF SILVER (3 AgO, C12HO), which does not become black on boiling. 7. Upon heating citric acid or citrates with concentrated sulphuric acid, carbonic oxide and carbonic acid escape at first, the sulphuric acid retaining its natural color; upon continued ebullition, however, the solution acquires a dark color, and sulphurous acid is evolved. 8 $164. d. MALIC ACID (2 HO, C, H ̧ O ̧), 1. Hydrate of malic acid crystallizes with great difficulty, forming crystalline crusts, which deliquesce in the air, and dissolve readily in water and in alcohol. Exposed to a temperature of 356° F., malic acid is resolved into MALEIC ACID (2 HO, C, H, O) and FUMARIC ACID (2 H O, CHO), which latter is upon continued application of heat also converted into the former. This deportment of malic acid is highly characteristic. If the experiment is made in a small spoon, pungent acid vapors of maleic acid are evolved with frothing effervescence. the experiment is made in a small tube, these fumes condense to crystals in the colder part of the tube. If 2. Malic acid forms with most bases salts soluble in water. The acid malate of potassa is not very difficultly soluble in water. Malic acid prevents, like tartaric acid, the precipitation of sesquioxide of iron, &c., by alkalies. 8 8 3. Chloride of calcium fails to produce a precipitate in solutions of free malic acid. Even after saturation with potassa or soda no precipitate is formed. But upon boiling, a precipitate of MALATE OF LIME (2 Ca O, C, H, 0, +6 aq.) separates from concentrated solutions. If the precipitate is dissolved in a very little hydrochloric acid, ammonia added to the solution, and the fluid boiled, the malate of lime separates again; but if it is dissolved in a somewhat larger quantity of hydrochloric acid, it will not reprecipitate, after addition of ammonia in excess, even upon continued boiling. Alcohol precipitates it immediately from a solution of the kind. Malate of lime, when heated with ammonia and nitrate of silver, fails to affect the reduction of the latter to the metallic state. 4. Lime-water produces no precipitate, either in solutions of free malic acid or in solutions of malates. 5. Acetate of lead throws down from solutions of malic acid and of malates a white precipitate of MALATE OF LEAD (2 Pb O, C, H ̧ O ̧ + 6 aq.). The precipitation is the most complete, if the fluid is neutralized by ammonia, as the precipitate is slightly soluble in free malic acid and acetic acid, and also in ammonia. If the fluid in which the precipitate is suspended is heated to boiling, a portion of the precipitate dissolves, the remainder fuses to a mass resembling resin melted under water. This reaction is distinctly marked only when the malate of lead is tolerably pure; if mixed with other salts of lead-if, for instance, ammonia is added to alkaline reaction, it is only imperfect or fails altogether to make its appearance. 6. Nitrate of silver throws down from solutions of neutral malates of the alkalies a white precipitate of MALATE OF SILVER, which upon boiling turns a little gray. 7. Upon heating malic acid with concentrated sulphuric acid, carbonic acid and carbonic oxide gas are evolved at first; the fluid then turns brown and ultimately black, with evolution of sulphurous acid. $165. Recapitulation and remarks. Of the organic acids of this group, oxalic acid is characterized by the precipitation of its lime-salt from its solution in hydrochloric acid by ammonia, and also by acetate of soda, as well as by the immediate precipitation of the free acid by solution of sulphate of lime. Tartaric acid is characterized by the difficult solubility of the acid potassa salt, the solubility of the lime salt in cold solution of soda and of potassa, the deportment of the lime salt with ammonia and nitrate of silver, and the peculiar odor which the acid and its salts emit upon heating. Citric acid is most strongly characterized by its deportment with lime-water, or with chloride of calcium and ammonia in presence of chloride of ammonium. Malic acid would be sufficiently characterized by the deportment of malate of lead when heated under water, were this reaction more sensitive, and not so easily prevented by the presence of other acids. The safest means of identifying malic acid is to convert it into maleic acid by heating in a glass tube; but this conversion can be effected successfully only with pure hydrate of malic acid. Malate of lead is difficultly soluble in ammonia, whilst citrate of lead dissolves readily in that agent; this different deportment of the lead salts of the two acids affords also a means of distinguishing between them. If only one of the four acids is present in a solution, lime-water will suffice to indicate which of the four is present; since malic acid is not precipitated by this reagent, citric acid only upon boiling, tartaric acid and oxalic acid already in the cold; and the tartrate of lime redissolves upon addition of chloride of ammonium, whilst the oxalate does not. If the four acids together are present in a solution, the oxalic acid and tartaric acid are precipitated first by chloride of calcium and ammonia, in presence of chloride of ammonium (the tartrate of lime separates under these circumstances completely only after some time; it is separated from the oxalate by treating with solution of soda); the citrate of lime is then thrown down by boiling, and the malate finally by means of spirit of wine. The precipitate produced by spirit of wine must never be taken positively for malate of lime, without further proof, since the sulphate and other salts of lime are also precipitated by that agent under the same circumstances. Positive conviction can only be attained by the production of hydrate of malic acid from the lime-salt. To effect this, the precipitate is dissolved in acetic acid, spirit of wine added, and the fluid filtered, if necessary. The filtrate is precipitated with acetate of lead, the fluid neutralized with ammonia, the precipitate washed, stirred in water, decomposed by hydrosulphuric acid, and the filtrate evaporated to dryness. 4 10 § 166. 8 8 10 4 Appendix: RACEMIC ACID, OR PARATARTARIC ACID (2 H O, C, H, O̟1). The formula of crystallized racemic acid is 2 HO, C, H, O,, +2 aq. The crystallization water escapes slowly in the air, but rapidly at 212° F. (difference between racemic acid and tartaric acid). To solvents the racemic acid comports itself like the tartaric acid. The racemates also show very similar deportment to that of the tartrates. However, many of them differ in the amount of water they contain, in form and solubility from the corresponding tartrates. Chloride of calcium precipitates from the solutions of free racemic acid and of racemates RACEMATE OF LIME (2 Ca O, CHO1+ 8 aq.), as a white crystalline powder. Ammonia throws the precipitate down from its solution in hydrochloric acid, either immediately or at least very speedily (difference between racemic acid and tartaric acid). It dissolves in solution of soda and potassa, but is reprecipitated from this solution by boiling (difference between racemic acid and oxalic acid). Lime-water added in excess, produces immediately a white precipitate insoluble in chloride of ammonium (difference between racemic acid and tartaric acid). Solution of sulphate of lime does not immediately produce a precipitate in a solution of racemic acid (diffe rence between racemic acid and oxalic acid); however, after ten or fifteen minutes racemate of lime separates (difference between racemic acid and tartaric acid); in solutions of neutral racemates the precipitate forms immediately. With salts of potassa racemic acid comports itself like tartaric acid. SECOND GROUP OF THE ORGANIC ACIDS. ACIDS WHICH CHLORIDE OF CALCIUM FAILS TO PRECIPITATE UNDER ANY CIRCUMSTANCES, BUT WHICH ARE PRECIPITATED FROM NEUTRAL SOLUTIONS BY SESQUICHLORIDE OF IRON: Succinic Acid, Benzoic Acid. 1. Hydrate of Succinic acid forms colorless and inodorous prisms or tables of slightly acid taste, which are readily soluble in water, alcohol, and ether, difficultly soluble in nitric acid, and volatilize when exposed to the action of heat, leaving only a little charcoal behind. The officinal acid has an empyreumatic odor, and leaves a somewhat larger carbonaceous residue upon volatilization. Succinic acid is not destroyed by heating with nitric acid, and may therefore be easily obtained in the pure state by boiling with that acid for half an hour, by which means the oil of amber, if present, will be destroyed. By sublimation crystalline |