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, C12 H ̧ 011), which, after washing, dissolves readily in animonia.

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6. Nitrate of silver produces in solutions of neutral citrates of the alkalies a white, flocculent precipitate of CITRATE OF SILVER (3 AgO, C12H, O), which does not become black on boiling.

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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.

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§ 164.

d. MALIC ACID (2 H O, C ̧ H ̧ O ̧),

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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, CH, O), 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.

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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.

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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.

§ 166.

Appendix: RACEMIC ACID, OR PARATARTARIC ACID (2 H O, C ̧ H ̧ O̟1).

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The formula of crystallized racemic acid is 2 HO, C, H, O1+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, C, H, O+ 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 (difference 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

needles of silky lustre are obtained; the hydrate loses water in this process, so that by repeated sublimation anhydrous acid is ultimately obtained. Heated in the air, succinic acid burns with a blue flame, free from soot.

2. The succinates are decomposed at a red heat; those which have an alkali or alkaline earth for base, are converted into carbonates in this process, the change being attended with separation of charcoal. Most of the succinates are soluble in water.

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3. Sesquichloride of iron produces in solutions of neutral succinates of the alkalies a brownish pale red, bulky precipitate of SUCCINATE OF SESQUIOXIDE OF IRON (Fe, O,, C, H, 0); one-third of the succinic acid is liberated in this reaction, and retains part of the precipitate in solution, if the fluid is filtered off hot. The precipitate dissolves readily in mineral acids; ammonia decomposes it, causing the separation of a less bulky precipitate of a highly basic succinate of sesquioxide of iron, and combining with the greater portion of the acid to succinate of ammonia, which dissolves.

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4. Acetate of lead gives with succinic acid a white precipitate of neutral SUCCINATE OF LEAD (2 Pb O, C, H, 0), which is very sparingly soluble in water, acetic acid, and succinic acid, but dissolves readily in solution of acetate of lead and in nitric acid. Treated with ammonia, the neutral succinate of lead is converted into a basic salt (6 Pb O, C, H, O).

5. A mixture of alcohol, ammonia, and solution of chloride of barium produces in solutions of free succinic acid and of succinates a white precipitate of SUCCINATE OF BARYTA (2 Ba O, C. H ̧ O ̧).

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6. Nitrate of suboxide of mercury and nitrate of silver also precipitate the succinates; the precipitates, however, are not possessed of any characteristic properties.

$ 168.

b. BENZOIC ACID (H O, C1, H, O,).

1. Pure hydrate of benzoic acid forms inodorous white scales or needles, or simply a crystalline powder. When heated, it fuses, and afterwards volatilizes completely. The fumes of benzoic acid cause a peculiar irritating sensation in the throat, and provoke coughing; when cautiously cooled, they condense to brilliant needles, when kindled, they burn with a luminous sooty flame. The common officinal hydrate of benzoic acid has the odor of benzoin, and leaves a small carbonaceous residue upon volatilization. Hydrate of benzoic acid is very sparingly soluble in cold water, but it dissolves pretty readily in hot water and in alcohol. Addition of water, therefore, imparts a milky turbidity to a saturated solution of benzoic acid in alcohol.

2. Most of the benzoates are soluble in water; only those with weak bases, e. g., sesquioxide of iron, are insoluble. The soluble benzoates have a peculiar, pungent taste. The addition of a strong acid to aqueous solutions of benzoates displaces the benzoic acid, which separates as hydrate in the form of a dazzling white, sparingly soluble powder. Benzoic acid is expelled in the same way from the insoluble benzoates, by such strong acids as form soluble salts with the bases with which the benzoic acid is combined.

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3. Sesquichloride of iron precipitates solutions of free benzoic acid incompletely; solutions of neutral benzoates of the alkalies completely. The precipitate of BENZOATE OF SESQUIOXIDE OF IRON (2 Fe, O, 3 [C, H, 0]+15 aq.), is bulky, flesh-colored, insoluble in water. It is decomposed by ammonia in the same manner as succinate of sesquioxide of iron, from which salt it differs in this, that it dissolves in a little hydrochloric acid, with separation of the greater portion of the benzoic acid.

4. Acetate of lead fails to precipitate free benzoic acid and benzoate of ammonia, at least immediately; but it produces white, flocculent precipitates in solutions of benzoates with a fixed alkaline base.

5. A mixture of alcohol, ammonia, and solution of chloride of barium produces NO precipitate in solutions of free benzoic acid or of the alkaline benzoates.

$169.

Recapitulation and remarks.-Succinic and benzoic acids are distinguished from all other acids by the facility with which they may be sublimed, and by their deportment with sesquichloride of iron. They are distinguished from one another by the different color of their salts with sesquioxide of iron, and also by their different deportment with chloride of barium and alcohol; but principally by their different degrees of solubility, succinic acid being readily soluble in water, whilst benzoic acid is very difficult of solution. Succinic acid is seldom perfectly pure, and may therefore often be detected by the odor of oil of amber which it emits.

The detection of the two acids, when present in the same solution with other acids, may be effected as follows: precipitate with sesquichloride of iron, warm the washed precipitate with ammonia, filter, concentrate the solution, divide it into two parts, and mix one part with hydrochloric acid, the other with chloride of barium and alcohol.

Succinic acid and benzoic acid do not prevent the precipitation of sesquioxide of iron, alumina, &c., by alkalies.

THIRD GROUP OF THE ORGANIC ACIDS.

ACIDS WHICH ARE NOT PRECIPITATED BY CHLORIDE OF CALCIUM NOR BY SESQUICHLORIDE OF IRON: Acetic Acid, Formic Acid.

1. The hydrate of acetic acid forms transparent crystalline scales, which fuse at 62.6° F. to a colorless fluid of a peculiar pungent and penetrating odor, and exceedingly acid taste. When exposed to the action of heat, it volatilizes completely, forming pungent inflammable vapors, which burn with a blue flame. It is miscible with water in all proportions; it is to such mixtures of the acid with water that the name of acetic