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made in the following manner :-Two small test-tubes are taken, fitted with perforated corks and tubes, as in
Fig. 12. the annexed figure. Into the test-tube A, the 27 suspected carbonate is to be placed, with only just sufficient water to cover the end of the tube at a. Sulphuric acid is then to be poured in at b, and the gas which issues from the tube c will then precipitate, from the baryta-water placed in the tube B, the white carbonate of barium. To assist in the detection of the gas where a small quantity only of material is present, the gas evolved may be drawn into the baryta-water by applying the mouth to the tube d, and so removing the original air from the test-tube B.
SALTS OF THE OXALIC RADICAL, OR OXALATES. The oxalates are very numerous, including salts of almost every basic radical, elementary or compound. Under ordinary conditions, oxalic acid and oxalates are very stable bodies. This radical forms an immense number of double salts, and many acid salts. The following formulæ represent some of these compounds :
H,C,0 MHC,O MCO, MH,C,0g. oxalic acid. acid oxalate. normal (or neutral) quadroxalate.
oxalate. Oxalates, when submitted to a slightly elevated temperature, decompose, leaving a carbonate of the metal and evolving carbonic oxide (CO), or leaving a residue of oxide and evolving both carbonic oxide and carbonic anhydride, thus :
Ca,C,0,=Ca, Co,+CO; or Zn,C,0,=Zn, 0+20+CO,. This difference in the products depends upon whether the carbonate of a base can withstand the temperature at which the oxalate decomposes. The oxalates of potassium, sodium, and calcium are found in the juices of various plants; and the hydrogen compound of this radical is also a very common product of the action of oxidizing bodies upon complex molecules.
THE HYDROGEN SALT (H,C,0,, or H, O), or oxalic acid, is a white crystalline solid, which sublimes between 100° and 162° without decomposition, and condenses in slender colourless needles : it is poisonous, and its vapour when breathed has a most irritating effect.
The oxalic radical may be detected both by certain insoluble salts, and by its decomposition.
Many oxalates are insoluble in water-in fact, the majority of the neutral salts : many of the acid salts are more soluble; but it is singular to find that, among the oxalates of the first subdivision, the acid salt is generally less soluble than the neutral one.
THE POTASSIUM and SODIUM Salts are comparatively soluble in water, although the latter (Na, C,0.) requires as much as 36:4 parts of cold, or 24:6 of boiling water for its solution.
THE BARIUM Salt is precipitated by adding chloride of barium to solutions of oxalic acid or oxalates : if the acid be employed, crystals of the acid oxalate speedily separate ; if a soluble oxalate, an immediate dense white precipitate of neutral oxalate will fall. The complete formula of the former salt is BaHC,0, +2aq; of the latter, Ba, 0, 0, +aq. They are both sparingly soluble in cold water; the acid salt dissolves more readily in hot water; they both dissolve also in chloride of ammonium solution. (See p. 85.)
THE STRONTIUM Salt is produced by the action of nitrate of strontium on oxalic acid or soluble oxalates. Its formula is Sr,C,0,. It is sparingly soluble in cold water, but only requires 19.2 parts of boiling water for solution. (See p. 88.)
The Calcium Salt is produced by the action of soluble calcium salts on oxalic acid or oxalates: it is a white granular precipitate.
Its formula is Ca,C,0,+aq.
It is insoluble in chloride of ammonium and in water; it is also insoluble in acetic acid, but dissolves in the stronger acids readily.
THE MAGNESIUM Salt is soluble.
THE FERROUS and SOME OTHER Salts of the third and fourth subdivisions are soluble; but the majority are sparingly soluble.
THE CUPROUS SALT is white; it is soluble in hydrate of ammonium.
THE CUPRIC Salt is a greenish blue precipitate. Its formula is Cu, C,0, +aq. It is soluble in neutral alkaline oxalates, and in hydrate, carbonate, and succinate of ammonium, but not in other ammonium salts. It is insoluble in water, in oxalic acid, and in warm dilute nitric acid. It dissolves in warm concentrated hydrochloric acid.
THE SILVER SALT (Ag, C,0.) is a white precipitate. It dissolves in hydrate and carbonate of ammonium, and in warm solutions of other ammonium salts. It is scarcely soluble in water, but dissolves in nitric acid.
THE MERCUROUS Salt is precipitated by the action of mercurous nitrate on oxalic acid or soluble oxalates: it is a white precipitate. Its formula is (Hg.),C,0,+aq. It is but slightly soluble in water or in dilute acids.
THE MERCURIC Salt is a white precipitate. Its formula is Hg, C,0,+aq. It is soluble in solutions of chloride and nitrate of ammonium, insoluble in water and dilute acids, somewhat soluble in sulphuric acid, and dissolved easily by other strong acids.
THE LEAD Salt is a white precipitate. Its formula is Pb, C,00 (dried at 140°). It is soluble in most ammonium salts, the hydrate and carbonate excepted; it is insoluble in water and in acetic acid, but soluble in nitric acid ; it is somewhat soluble in oxalic acid.
The oxalates may be detected by the decomposition of their acid-radical.
a. When to an oxalate some strong sulphuric acid is added, and the mixture warmed, the oxalic acid thus liberated undergoes instant decomposition, partly from the tendency of sulphuric acid to form a hydrate :
H,C,0,+H, SO,=H, SO, H,0+CO+COZ. Considerable effervescence ensues from the escape of the carbonic anhydride and carbonic oxide gases; and the latter gas will be found to burn with a blue flame. This action of sulphuric acid, without any blackening of the substance under examination, points decisively to the presence of oxalic acid; for though the salts of some of the more complex acid-radicals yield carbonic oxide also, they blacken simultaneously, the ferrocyanides excepted.
B. If, instead of sulphuric acid alone, a mixture of binoxide of manganese (Mn, 0,) and sulphuric acid be made to act upon oxalic acid, the sole gaseous product of the reaction is carbonic anhydride (CO2).
SALTS OF THE BORACIC RADICAL, OR BORATES. These salts are by no means of such frequent distribution in nature as the carbonates; they occur in some few minerals, and in greater abundance in the hot lakes or boracic lagoons of Tuscany, into the waters of which the vapours are conveyed which rise from the volcanic bottom. These vapours, which are charged with boracic anhydride (Bo,0z), yield it to the water, with which it combines to form boracic acid. It is generally met with in commerce combined as borax, the biborate of sodium.
Most borates may be heated on charcoal without decomposition. The use of borax as a blowpipe reagent is well known.
THE HYDROGEN SALT crystallizes from a hot aqueous solution; but if these crystals be heated, they evolve water, and yield a fused glassy substance, which is the so-called anhydrous acid (Bo,0z). This body bears the same relation to boracic acid as chromic anhydride does to chromic acid. When dissolved to saturation in hot water, it separates on cooling, in the form of hexagonal laminæ having a pearly lustre and the formula HB00, +aq. It may be considered as the representative of what are called the monoborates, which have the formula MB00, +naq. If these crystals be heated to a temperature considerably above 100°, they part with the elements of water, and another hydrogen compound is obtained (H, Bo,0,), which, when written without its 2 eqs. of accidental water, becomes H, Bo, Oq, and may then be considered as the type of the biborates. The biborates may
also be viewed (like the bichromates) as combinations of the anhydride (Bo,0z) with the monoborates ; thus we have the following equation when we disregard water of crystallization :
2HB00,+Bo, 0,=H, Bo,Oc. The rationale of the process whereby the biborates are produced may be as follows:—we may suppose that, under the influence of heat, 1 molecule of the anhydride (Bo,0z) is formed from 2 equivalents of boracic acid, thus :
2(HB00,, H,0)=B0,03+38,0; the body, Bo, 0,, thus formed, then unites with 2 equivalents of undecomposed acid to form the biborate of hydrogen. Or we may merely express the change as follows :
4(HB00,, H,0)=H, B0,0,, 21,0+3H, 0. Borates, then, may be of at least two classes, borates and biborates. The latter salts are much more stable than the formerso much so, indeed, that even the potassium salt of the former series, by mere exposure to the air, absorbs carbonic anhydride, and becomes converted into the carbonate and biborate, thus
4KB00, +C0,=K,CO,+K, Bo,Oc Nor are these the only classes of borates. Just as boracic anhydride combines with borates to form biborates, so additional proportions of this body yield salts which have been called ter-, quadri-, and sex-borates. The formulæ of the sodium (or potassium) salts of these compounds are
Borate Na Bo 0,
Sexborate Na, B022016=2NaBo0, +5B0,0z. The borates, biborates, and sexborates are pretty well known; but not so the others.
The boracic radical may be recognized both by the formation of sparingly soluble salts, and by processes of decomposition.
The normal borates are more soluble in water than the others. Of the biborates, which are the most common boracic salts,