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(HTaO2), which, on addition of excess of the precipitant, is redissolved, but again separates on the addition of sulphuric acid and subsequent ebullition, a compound of that acid with tantalic acid being produced.

B. If into the sulphuric acid precipitate (just mentioned) still remaining in the slightly acid liquid a strip of zinc be plunged, as it dissolves, a fine blue colour will be imparted to the liquid ; this tint will, however, change to a brown, and, finally, brown flakes will separate, which, after some time, will become oxidized, and converted into tantalic acid.

7. Precipitated tantalic acid is insoluble after ignition, in all acids, and must, like ignited silica (Si,O,), be fused with hydrate or carbonate of sodium.

8. Hydrosulphuric acid does not precipitate an acid solution of tantalic acid.

e. In a slightly acidified solution of tantalic acid, ferrocyanide of potassium produces a yellow precipitate, and ferricyanide a white.

Of compound acid-radicals containing niobium and oxygen, one is known, the radical of niobic acid. Of its salts, the niobiates, almost all that has been said regarding the tantalates equally well applies. The acid is, however, more completely separated from its salts than tantalic acid is from tantalates, on the addition of sulphuric acid, not requiring the aid of heat.

Of compound acid-radicals containing pelopium and oxygen, one is known, that existing in pelopic acid. Its salts bear the closest resemblance to the tantalates and niobiates.

SALTS OF THE TITANIC RADICAL, OR TITANATES. Two combinations of titanium with oxygen are known; the lower oxide has not, however, been observed to manifest any tendency to pass into an acid-radical. The titanic radical occurs in numerous minerals. In Titanite it occurs as titanate of calcium (Ca, Ti, 0,) associated with silicate of calcium, while it is most frequently found in the varieties of titaniferous iron, one of which, Ilmenite, is the ferrous titanate (Fe, Ti,o,).

Titanic acid when heated before the blowpipe yields the infusible titanic oxide Ti,0,. The titanates are not generally decomposed by fusion, but, on the contrary, many salts of this radical are prepared by fusing titanic oxide with metallic carbonates.

THE HYDROGEN Salt is prepared just as the analogous compound of silicon, by the gradual addition of an acid. It is a white, flocculent, and bulky precipitate, and consists (when dried in vacuo over sulphuric acid) of the pure substance H, Ti,Og. The acid thus obtained, if washed with cold, not with hot water, dissolves readily in acids, but not in the hydrates of the first subdivision, and only to a trifling extent in alkaline carbonates. When the acid solution of titanic acid is diluted with much water and boiled, a precipitate occurs, probably of the body (Ti 0,) already mentioned as obtained by the ignition of the acid. It is a white precipitate, becoming yellow on heating. It is quite insoluble in water, and in all acids except hydrofluoric

and boiling sulphuric acids. It occurs naturally in the minerals Rutile and Anatase.

The titanates are, for the most part, insoluble in water. The monotitanates of the first subdivision are decomposed by water into a basic salt, which dissolves, and an acid salt, which is precipitated. The barium, calcium, silver, mercury, and lead salts are unknown.

This acid-radical is recognized by the following processes of decom. position :

a. When the hydrochloric solution of titanic acid is diluted and boiled, the oxide or anhydride (Ti,,) separates as a white powder.

B. The oxide Ti,o, requires fusion with carbonate of sodium to render it soluble.

y. If into the hydrochloric solution of titanic acid a strip of zinc be introduced, a blue solution will be obtained; and from this a reddish or violet precipitate will separate, which gradually oxidizes into the white titanic acid.

d. Titanic anhydride (Ti,02), when fused with microcosmic salt in the reducing flame, gives a violet-blue bead on cooling: the colour is rendered more evident after the addition of tin. If iron be present, a yellow or bloodred bead will be produced in the reducing flame.

6. Hydrosulphuric acid does not precipitate an acid solution of titanic acid.

%. Ferrocyanide of potassium gives a dense orange brown precipitate in a solution of titanic acid in weak hydrochloric acid. The precipitate is soluble in excess of the precipitant.

SALTS OF THE SULPHOCARBONIC RADICAL, OR SULPHOCARBONATES. These salts are usually of a yellow, red, or brown colour; many of them decompose with rapidity into sulphides. They closely resemble the car. bonates in constitution, the oxygen of those salts being replaced by sulphur, thus K, C,03,

K, C,Sg. carbonate of

sulphocarbonate of potassium.

potassium. On a slight increase of temperature, the sulphocarbonates decompose into bisulphide of carbon (CS,) and metallic sulphides.

THE HYDROGEN SALT (H, 0,8g) or sulphocarbonic acid, is a reddish brown, transparent, oily liquid, denser than water; it has a very peculiar odour, and is prone to decompose into hydrosulphuric acid and the body CS, which is the sulphocarbonic anhydride, and bears to sulphocarbonic acid the same relation that carbonic anhydride (CO2) bears to carbonic acid (H, CO,).

The sulphocarbonates may be recognized by certain insoluble compounds, and also by their products of decomposition.

The soluble sulphocarbonates have a saline and somewhat sulphureous taste; those of the first and second subdivisions are soluble in water, as are also some members of the third subdivision.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM SALTS are soluble.

THE CUPRIC SALT is red-brown when precipitated from sulphocarbonic acid, dark brown when from sulphocarbonate of calcium (Ca, CS3); it is soluble in excess of its precipitants; it becomes black on drying.

THE SILVER SALT is produced by the action of sulphocarbonate of calcium on silver salts: it is a dark brown precipitate, which becomes black on drying. It is soluble in excess of its precipitant.

The Mercuric Salt is yellow when precipitated by sulphocarbonate of ammonium ([NH,), CS), black when the calcium salt is employed. The yellow salt passes from yellow to orange red and black, with evolution of bisulphide of carbon.

The Lead Salt is dark brown when precipitated by sulphocarbonate of calcium, but red when sulphocarbonic acid or the ammonium salt is employed; it rapidly becomes black from separation of sulphide of lead (Pb, 8).

The sulphocarbonic radical may be readily distinguished by the following tests:—

a. When to the solution of a sulphocarbonate a strong acid is added, the sulphocarbonic acid liberated is at once decomposed into hydrosulphuric acid and the oily body, bisulphide of carbon (CS,), both products being easily identified not only by their reactions but by their unmistakeable and unpleasant odour :

H, CS,=H, S+CS. B. If the aqueous solution of a sulphocarbonate be evaporated two or three times with excess of sulphide of ammonium, and the resulting mass dissolved in water, filtered, and the solution then tested with ferric chloride (Fe, Cl,), the magnificent blood-red colour of sulphocyanide of iron will be produced.

This radical is perhaps best recognized by the formation, &c. of the mercuric and lead salts, and by the tests a. and ß.

SECTION III.-The cyanides, cyanates, and sulphocyanides; the

ferrocyanides, ferricyanides, and cobalticyanides ; the formiates, acetates, benzoates, succinates, tartrates, lactates, ci

trates, gallates, tannates, and urates. SALTS OF THE COMPOUND ACID-RADICALS WHICH CONTAIN

CARBON AND NITROGEN; CARBON, NITROGEN, AND OXY-
GEN; CARBON, NITROGEN, AND SULPHUR; CARBON, NI.
TROGEN, AND METALS; CARBON, OXYGEN, AND HYDRO-
GEN; AND CARBON, OXYGEN, HYDROGEN, AND NITRO-
GEN.

To these salts the term “organicis generally applied, from their naturally occurring almost solely in the organic kingdoms

of nature. Many of these bodies do not, however, occur actually in nature, but are the artificial products of a chemical action upon natural substances. It was thought till recently that the building up of complex molecules from the common and simpler bodies at his disposal was not within the power of the chemist : but the experiments of recent years have shown this to be a fallacy; for, by skilful manipulation and ingenuity of contrivance, many most complicated substances have been artificially constructed. Numerous bodies have not yet been thus produced; but their number is constantly diminishing. By a consideration of the members of this section, it will be seen that they are often arranged in series, somewhat after the manner of the borates, already alluded to; and it needs but little discernment to predict that, if by a certain process one member of such a series can be formed, by a slight variation of the experiment to suit the circumstances of the special case, every member of the group may probably be produced at will. The invention of a method is a discovery; but the production of all subsequent members of the series is but the application of a principle.

Of acid-radicals formed by the union of carbon with nitrogen, one only is of any analytical importance, viz. cyanogen.

SALTS OF CYANOGEN, OR CYANIDES. These bodies occur in some few organic products; and the radical may also be formed directly from its elements by exposing hydrate or carbonate of potassium to the joint action of carbon (or carbonic oxide) and nitrogen, at a high temperature. This action has been made to take place by employing charcoal saturated with the salts just mentioned, and heating it strongly in a vertical shaft to which the nitrogen, &c. of a furnace-flue was admitted by appropriate openings. The radical is thus obtained in combination with potassium. It may also be obtained by the decomposition of ferrocyanide of potassium. (See p. 53.)

The cyanides of the first subdivision may be fused without decomposition, excepting the ammonium salt, which volatilizes unchanged; the fusion may be effected on charcoal. The cyanides of the second subdivision also sustain a high temperature without change. Many other cyanides, however, decompose into cyanogen gas and metal, or into cyanogen gas and a mixture of the metal with a paracyanide: such cyanides are the silver and mercuric salts. Others, again, are resolved into their elements—carbon, nitrogen, and metal; e.g. cyanide of lead (PbCN or PbCy).

THE HYDROGEN SALT (HCN or HCy), hydrocyanic or prussic acid, is remarkable as being one of the most terrible poisons known. It is a transparent, colourless, mobile liquid of sp. gr. 0.705–0.710 at 6° C.; it freezes at — 15°, boils at 270.5, and volatilizes in the air with such rapidity, that the cold produced by the evaporation of a portion freezes the remainder : it is inflammable, burning with a pale blue flame. In a state of great dilution, it is used in medicine. Pure hydrocyanic acid and its aqueous solution, if tolerably concentrated, rapidly decomposes, yielding ammonia and a brownish black powder. The presence of a trace of mineral acid prevents this change; but a large quantity of a strong acid itself causes a decomposition, the hydrocyanic acid then yielding an ammonium salt and formic acid, thus

HCN+HCl+2H,O=NHCl+HCHO. hydrocyanic

formic acid.

acid. This radical may be detected both by the formation of insoluble salts and by its products of decomposition; also by certain complex bodies which it may be made to yield.

Regarding the solubility of cyanides, it may be stated that the salts of the first and second subdivisions are readily soluble in water: for the bases of the first half of the third subdivision this radical exhibits little affinity; but the cyanides of iron, manganese, cobalt, nickel, and zinc, and those of the fourth subdivision, are for the most part insoluble in water. The insoluble cyanides all exhibit the peculiarity of dissolving in excess of alkaline cyanide, to form compounds in which a new, and often very stable, compound acid-radical is believed to exist. Such a change is represented, in the case of iron, by the following equations :

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