PHOSPHORIC AOID.

395

form a soluble phosphate, it may be distinguished from all other acids by the fol-lowing characters: it throws down, with the soluble salts of lime, lead, andbaryta, white precipitates {phosphates) soluble in nitrie acid: with the nitrate ofsilver it causes a yellow precipitate {subscsqitiplwsphate of silver) soluble in nilricacid and in ammonia: hydrosulphuric acid causes no change of colour or precipi-tate with it: if the soluble phosphate be heated to redness, it is converted into apyrophosphate, which gives, with the nitrate of silver, a white precipitate (pyro-phosp/iale of silver.)

Purity. —The following are the qualities of this preparation, as given in theLondon Pharmacoposia:—

"Chloride of barium or nitrate of silver being added, whatever is thrown down is readilydissolved by nitrie acid. Strips of copper and silver are not at all aeted upon by it, nor is it.coloured vvhen hydrosulphuric acid is added. Its sp. gr. is 1064; 42 grs. of [crystallizedlcarbonate of soda are saturated by 100 grs, of this acid, and nothing is thrown down."

The chloride of barium is to detect sulphuric acid: while the nitrate of silverdetects hydrochloric acid. Should any free nitrie acid be present, a portion ofthe copper and silver would be dissolved; and the Solution would yield a darkprecipitate with hydrosulphuric acid. The quantity of carbonate of soda satu-rated indicates the per-centage strength to be 10-5. The absence of any precipi-tate, on the addition of carbonate of soda, shows that no phosphate of lime or anyother earthy phosphate is present.

Composition. —Pure anhydrous phosphoric acid is thus composed:-—■

Jitoms..... 1 ...

Eq. Wt...... 16 .....

Per Cent.... 55-50 .....

Berzelius.... 55-95 ....

Dulovfr.... 44.8 ....55-2 ...

Davy

.... 57 4

..... 36.....

... 10000 .....

... 100-00 ....

... 1000 ...

.... 100 0

Mr. Phillips sa3^s, that 100 grains of the diluted acid of the Pharmacopqniasaturale 42 grains of [crystallized] carbonate of soda. This indicates its compo-sition to be as follows:—

By Weicht.

Phosphoric Acid .................................................. 10-5

Water............................................................ 80 5

Diluted Phosplioric. Acid, Pk. L .................................... 100 0

Physiological Effects. a. On Vege/ablcs. —This acid is poisonous to plants.(Gceppert, quoted by De Candolle, Phys. Veget.)

ß. On Jinimals. —Very few experiments have hitherto been made with it onanimals. Orfila (Toxicolog. Gener.) found that a streng Solution of it aeted likesulphuric acid. Thrown into the veins of a dog, it coagtilated the blood andkilled the animal within ten minutes. Introduced into the stomaeh, it aeted as apowerfully corrosive poison.

y. On Man. —Diluted phosphoric acid produces the nsual effects of the dilutedmineral acids, and which I have before noticed (pp. 192, 198, and 207.) It is,therefore, denominated tonic and refrigerant, and may be employed whereverthe mineral acids are indicated. It is milder, more assimilable, and, therefore,less likely to disagree with the digestive Organs, than sulphuric acid, with which,in its action, it is usually compared. These qualities it perhaps derives from itsbeing, as Burdach {Arzneimittellehre, Bd. 3. S. 395. 1809.) expresses it, "lessheterogeneous to the human organism, since it has a considerable share in thecomposition of it." The same authority also observes, that besides fulfilling theindications of the mineral acids, " it much exalts the excitability when theorganism is weak."

Various effects have been ascribed to this acid, which require to be fartherinvestigated ere they are admitted. Thus Hecker {Arzneimittel. Bd. 2. S. 305.)says, it exerts a special influence over the neryous system, in virtue of which itpossesses the power of allaying pain and spasm. Lentin {Beitrage zur ausüb,