Obrazy na stronie
PDF
ePub

Malic acid has been lately detected in the acid liquid obtained from ants. When this acid liquid is saturated with lime, and mingled with acetate of lead, a precipitate is obtained which is malate of lead, which

may

be decomposed by the affusion of sulphuric acid.

Rationale. În Experiment 1, the malate of potash, which is formed, is decomposed by acetate of lead ; malate of lead is precipitated, and acetate of potash remains in solution. The former is treated with sulphuric acid, which disengages the malic acid. In Experiment », the acetate of lead acts nearly in the same manner; in Experiment 3, malic acid is obtained by the decomposition of nitric acid.

Remark. This acid is found ready formed in the juice of unripe apples, and in those of barberries, elderberries, gooseberries, plums, and the common house-leek.

Malic acid is incapable of crystallizing, but appears always in the liquid state, of a reddish brown colour. Its taste is an unpleasant. sour. If left exposed to the air, it gradually undergoes a spontaneous decomposition. Nitric acid converts it into oxalic acid. It forms precipitates in the solution of nitrate of mercury, lead, and silver.

[ocr errors]

SECTION XXXIII.

OF SUBERIC ACID.

Experiment 1. Introduce one part of cork cut into small pieces into a retort, and pour upon it six of nitric acid, distil the mixture with a gentle heat till no more nitrous gas appears. Then pour the contents into a basin, and evaporate it till it acquires the consistence of honey, and a pungent suffocating vapour arises; then add to it twice its bulk of boiling water, heat it gently, and pour it on a filter. The fluid which passes, when cooling, deposits a precipitate, which must be separated; the fuid is then evaporated to dryness, and the product obtained is suberic acid.

Rationale. The nitric acid is decomposed ; its oxygen unites with the cork, converting it into an acid, whilst nitrous gas is liberated.

Remark. Suberic acid is not crystallizable, but it may be produced in the solid form of a powder, or thin pellicles. It is volatilized by heat. Suberic acid has a sharp, acid, bitterish taste. It acts strongly upon the throat, and excites coughing. It strongly reddens vegetable blues, and has the peculiar property of turning the blue colour of a solution of indigo in sulphuric acid, of the nitrate of copper, and of the sulphate of copper to green, and gives a yellow colour to the solution of green sulphate of iron, and to the solution of sulphate of zinc. It is difficultly soluble in cold but easily soluble in boiling water. When heated it first fuses, then becomes dry, and at last sublimes entirely.

This acid was discovered by Brugnatelli, and its properties were afterwards more investigated by Lagrange.

SECTION XXXIV.

OF FORMIC ACID.

Experiment 1. If ants be infused in water, the water distilled off as long as it comes over without any burnt smell; the liquor saturated with potash, and evaporated to dryness; the dry mass saturated with sulphuric acid, and again distilled, formic acid will be obtained.

Rationale. The acid of the ant is taken up by the water, and afterwards continued with potash; the bombate of potash, thus formed, is then distilled with sulphuric acid, and the bombic acid is disengaged.

Remark. This acid was found to exist many years ago in the formica rufa, or red ant, and many of its properties were investigated by Margraff; and al

though Fourcroy and Vauquelin endeavoured to prove that it was only a mixture of acetic and malic acids, yet from subsequent experiments it is found to be a distinct acid. This acid is colourless, has a peculiar smell, and unites with different bases..

SECTION XXXV.

OF PRUSSIC ACID.

Experiment 1. Put into a glass matrass two parts of pulverized Prussian blue, one part of red oxyd of mer. cury, and six parts of water; boil this mixture for half an hour, agitating it frequently, then filter it, and pour over the residuum two parts more of boiling water, having united the liquors, evaporate the whole to obtain crystals, and prussic acid will be formed.

Rationale. The prussic acid quits the oxyd of iron to unite to the oxyd of mercury, with which it forms prussiate of mercury, which can neither be decomposed by acids nor alkalies. In order to disengage from it the prussic acid, dissolve it in water, or take the li-quor above mentioned, not concentrated: pour the quantity obtained in the preceding experiment into a bottle containing about an ounce of iron filings, add nearly three ounces of concentrated sulphuric or muriatic acid, and shake it well for some minutes: the mixture now becomes black, for the iron unites to the oxygen of the mercury, and combines with the acid. Leave the fluid at rest, and then decant it, and put it into a retort placed on a sand bath; adapt to the retort a receiver, containing a little distilled water, to absorb the acid, and carefully lute all the joinings. By the help of a gentle heat, the prussic acid, being more volatile than water, will pass over first; and when about a fourth of the liquor has passed, stop the operation.

The liquor which passes contains a little sulphuric acid : to free it from this acid, distil it again with a ve-i'y gentle heat from pulverized chalk, and prussic acid will be obtained in the greatest purity.

Experiment 2. If a mixture of two parts of prussian blue, one of sulphuric acid, and one of water be distilled, prussic acid will come over.

Experiment 3. Prussic acid may be obtained by distilling two parts of prussiate of potash with one of sulphuric acid, previously diluted with an equal quantity of water; the prussic acid becomes disengaged, and is absorbed by the water previously put into the receiver; or by distilling bitter almonds, the kernels of peachstones, or the leaves of the cherry-laurel (lauro cerasus, Lin.) with water.

Remark. Scheele succeeded in forming prussic acid by causing a current of ammoniacal gas to pass through red hot charcoal. Oxy-prussic acid, of Berthollet, is formed by treating prussic acid with oxymuriatic acid.

This acid derives its name from the pigment called Prussian blue, of which it forms a component part.

It was first obtained in a separate state by Scheele.

Prussic acid exists in the form of a colourless fluid. It has a strong odour, greatly resembling that of peach tree flowers, or of bruised bitter almonds. Its taste is sweetish, pungent, and somewhat acrid. It is very volatile, and inflammable when in the state of vapour or gas. It does not redden the most delicate vegetable blues, and unites difficultly with alkalies and earths in the direct way. It is easily decomposable by light, heat, or oxygenized muriatic acid at high temperatures; it becomes converted into ammonia, carbonic acid, and carburetted hydrogen gas. It does not act upon any of the metals, but readily unites with most of their oxyds, with which it forms highly insoluble com. pounds. It has a great tendency to form triple compounds with alkalies and metallic oxyds, and in that state it decomposes all metallic salts, and hence it is one of the most important re-agents of the chemist. It is composed of hydrogen, carbon, and azote.

Prussic acid united with potash is employed as a reagent; its use may be seen in the following experiments :

Experiment 4. Into a wine glass of water put a few drops of prussiate of potash, and a little dilute solution of sulphate of iron into another glass: by pouring these two colourless fluids together, a bright deep blue colour will be immediately produced, which is the true prussian blue.

Experiment 5. Put some prussiate of potash into one glass; into another a little nitrate of bismuth. On mixing these colourless fluids, a yellow will be the product.

Experiment 6. Pour a little prussiate of potass into a glass containing a colourless solution of sulphate of copper, and a reddish brown will be produced, being a true prussiate of copper.

Experiment 7 Take water holding carbonate of iron in solution, and add some diluted prussiate of potass; prussian blue will be formed by the mixture.

Experiment 8. Take some of the same water as that used in the last experiment; boil it, and now add prussiate of potash. In this case no colour will be produced.

SECTION XXXVI.

OF GALLIC ACID.

For the following method of obtaining gallic acid we are indebted to Mr. Fiedler :

Experiment 1. Dissolve two ounces of alum of commerce in water, and precipitate the solution, by letting fall into it a solution of potash ; wash the precipitate well, and transfer it into an aqueous infusion of gallnuts (obtained by infusing 1 ounce of galls into 16 of water, and evaporating the infusion to one half) agitate the mixture frequently during the course of 24 hours, and transfer it on a filter. The ffuid which passes through the filter is gallic acid; it may be obtained in the form of needle-shaped crystals by evaporating it

« PoprzedniaDalej »