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SECTION III.

OF PHOSPHORIC ACID.

Experiment 1. If phosphorus be burnt in oxygen gas; a product will be obtained, which appears first in white fumes, called dry phosphoric acid. Or,

Experiment 2. If nitric acid be added to phosphorus. from time to time, until the effervescence ceases, the same acid will be produced.

Rationale. Phosphorus by combining with oxygen forms either an oxyd or an acid: in the first experiment it unites with oxygen by combustion; in the latter by the decomposition of nitric acid, nitric oxyd being formed. Phosphoric acid, for the purpose of making phosphorus, is prepared in the following way:

Experiment 3. Dilute in a spacious glass jar one pound of sulphuric acid with six or eight pounds of water; then add gradually, and with constant stirring, one pound and a half of finely pulverised bones burnt to whiteness. An effervescence will take place. When this has ceased, leave the whole on a gentle sand-bath for a few hours, taking care to stir it frequently, and to supply the loss of water which happens by evaporation. After it has been suffered to remain undisturbed, strain the whole through a cloth, and wash the residual matter repeatedly in water till it passes tasteless. The fluid thus obtained contains the phosphoric acid, contaminated with lime, and may be evaporated in a Wedgwood's, or glass basin, to any wished for consistence. See Phosphorus.

Remark. The acid produced in this way is not pure; to obtain it so, carbonate of ammonia must be added until no more precipitate falls down; the precipitate is carbonate of lime, which must be separated by filtration : the fluid being then evaporated to dryness leaves plosphate of ammonia. This is exposed to heat in a china cup, till all the ammonia is disengaged, which may be known by

the mass frothing no longer, but flowing quietly. On cooling, it congeals into a transparent vitreous substance, called glacial acid of phosphorus, which attracts moisture, and is soluble in water.

Experiment 4. If solid phosphoric acid be exposed to the air, it will deliquesce.

Rationale. This takes place by the absorption of moisture from the air.

Experiment 5. If liquid phosphoric acid be put into a platinum crucible, and exposed to the heat, a transparent gelatinous mass will be formed; but,

Experiment 6. If the heat be increased, it will take the appearance of melted glass, which, when cold, is called phosphoric glass.

Rationale. The exposure to heat disengages the watery portion, leaving the phosphoric acid in a dry state.

Experiment 7. If this acid be mixed with charcoal powder and distilled, phosphorus will be obtained. See Phosphorus.

Phosphoric acid acts only on a small number of metallic substances. Its union with alkalies, earths, and metallic oxyds forms a class of salts called phosphates. Phosphoric acid is composed of 46.5 phosphorus, and 53.5 oxygen in the hundred,

SECTION IV.

OF PHOSPHOROUS ACID.

Experiment 1. If a few sticks of phosphorus be. ex. posed to the action of atmospheric air, in a glass funnel, phosphorus acid will be formed, and may be collected in a bottle placed underneath. Two or three pieces of broken glass fixed in the neck of the funnel to support the phosphorus, and a small quantity of distilled water put into the receiving bottle, complete this

simple apparatus. The pieces of phosphorus should be placed so as not to touch each other.

Remark. When phosphorus is burnt slowly, as in the above experiment, it forms an acid different from the phosphoric. It was called phlogisticated phosphoric acid by Morveau.

Phosphorous acid is liquid, has an unpleasant taste, and emits an alliaceous and disagreeable odour when rubbed, and especially if warmed. When heated more strongly,

, part of it is volatilized in the form of a white vapour.

Exposed to the air, or to oxygen gas, the phosphorus acid is converted into the phosphoric acid.

Its union with different bases, forms phosphites.

SECTION V.

OF CARBONIC ACID.

of gas.

Experiment 1. If diluted sulphuric acid be added to marble, carbonic acid will be disengaged in the state

Experiment 2. If water be impregnated with carbonic acid gas, which may be effected by means of a Nooth's apparatus, or by employing artificial pressure, the liquid carbonic acid, or ærated water will be formed.

Remark. Carbonic acid is composed of 18 parts carbon and 82 oxygen; which has been ascertained by analysis as well as synthesis.

Experiment 3. Put a small piece of phosphorus into a crucible, cover it closely with common chalk, so as to fill the crucible. Let another crucible be inverted upon it, and both subjected to the fire. When the whole has become perfectly red hot remove them from the fire, and when cold, the carbonic acid of the chalk will have been decomposed, and the black charcoal, the basis of the acid, may be easily perceived amongst the materials.

Remark. Carbonic acid gas is found in abundance in many natural waters, Those of Pyrmont, Spa, and Seltzer, are instances; the last particularly is highly impregnated with this acid.

Experiment 4. To a glass of water, suspected to contain carbonic acid, add a small quantity of any of the other acids. If carbonic acid be present, it will become visible by a sparkling appearance on the sides of the glass and surface of the Auid.

SECTION VI.

OF FLUORIC ACID.

Experiment 1. Put one part of fluate of lime in coarse powder into a leaden or tin retort, and pour upon it two parts of sulphuric acid. Lute the retort to a receiver of the same metal, containing one part of water, and apply a gentle heat. The fluoric acid gas disengaged will be absorbed by the water and form li. quid fluoric acid, which must be kept in well-closed leaden or tin bottles, or phials coated within with wax or varnish.

Rationale. The sulphuric acid, by virtue of a supe. rior affinity, unites with the lime of the fluate, forming sulphate of lime, and the fuoric acid gas is disengaged. United to water, it forms liquid fuoric acid.

Remark. Fluoric acid combined with different bases forms saline compounds, called Aluates.

The distinguishing property of fluoric acid is, its power of dissolving and volatilizing silica. Its odour resembles muriatic acid.

To preserve the liquid acid it must be kept in bottles lined on the inside with wax dissolved in oil, or in vessels of lead or platina.

See Fluoric Acid Gas.

SECTION VII.

OF BORACIC ACID.

Experiment 1. If to a concentrated solution of borax in hot water, sulphuric acid be added, small crys. tals will gradually form, and fall to the bottom as the liquor cools, which is boracic acid. Or,

Experiment 2. Dissolve any quantity of sub-borate of soda, or borax in boiling water, and add to this solution sulphuric acid, by a little at a time, till the solution be rather more than saturated. Then evaporate it slowly to one-third, and set it aside to cool; white scales will be deposited, which are boracic acid. After all the acid has been crystallized out of the solution, the salt must be re-dissolved, re-crystallized, and lastly washed in distilled water, drained on filtering paper, and then dried.

Rationale. In both these experiments, the sulphuric acid unites with the soda, forming sulphate of soda, which remains in solution, and the boracic acid is separated,

Remark. Boracic acid may likewise be obtained by sublimation, from two parts of sur-saturated borate of soda, one of sulphuric acid, and one of water.

The union of boracic acid with different bases forms salts, called borates.

This acid exists united to soda in the salt called borax, or sub-borate of soda. United to lime and magnesia, it forms the mineral called borate of lime.

Boracic acid appears in brilliant, glittering, white, hexahedral scales, soft and unctuous to the touch. Its taste is bitterish, with a slight degree of acidity. It is soluble in alcohol, which it causes to burn, when set on fire, with a green flame, surrounded with a white one.

Experiment 3. If a spoonful of good alcohol and a little boracic acid be stirred together in a tea-cup, and then set on fire, they will produce a very beautiful green lame.

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