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Analysis of Subdivision I.
The acid-radicals of more common occurrence only being included,
the salt may be a CHLORIDE, BROMIDE, IODIDE, FLUORIDE, HYPOCHLORITE, CHLORATE, BROMATE, IODATE, or a CHLOROPLATINATE.
Evidence of the presence of any one of these salt-radicals may be obtained by adding to the solid salt, or its strong solution, some concentrated sulphuric acid. The following effects will be produced, either immediately or on warming the mixture:Pungent colourless vapours (of HCl) indicate a chloride. red-brown
of Br) indicate a bromide or bromate. violet
(of I) indicate an iodide or iodate. colourless , (of HF), etching glass, indicate a fluoride. yellow
(of C1,0), having the odour of bleaching
powder, indicate a hypochlorite. orange yellow , (of C1,02), explosive, indicate a chlorate.
If no precipitate, the solution may contain
Cl, Br, or I;
AgCl, AgBr, or Agi.
Yellow residue | If wholly dissolved, test a porof AgI indicates tion of the original solution by
means of Mn, o, and H,SO, for
CÍ or Br.
SUBDIVISION II. SALTS OF OXYGEN, SULPHUR, SELENIUM, AND TELLU.
RIUM, AND OF THE CHIEF COMPOUND ACID-RADICALS INTO THE COMPOSITION OF WHICH THEY ENTER. The members of this subdivision present many analogies with those of the preceding; three of them, sulphur, selenium, and tellurium, bear the closest relation to each other, exhibiting a curious progression towards the basic character, whilst a fourth, oxygen, has a more distant resemblance. In addition to the salts which these form by direct combination with basic radicals, there are many others in which sulphur, selenium, and tellurium exist in the form of a compound acid-radical containing oxygen or a metal. The majority of the salts of this subdivision are bibasic; some, however, are tribasic.
Section 1.-SALTS OF OXYGEN, SULPHUR, SELENIUM, AND
Section II.-SALTS OF THE COMPOUND ACID-RADICALS WHICH
CONTAIN SULPHUR, SELENIUM, AND TELLURIUM COM.
The hyposulphites, sulphites, hyposulphates, trithionates, tetrathionates, pentathionates, and sulphates ; the selenites, seleniates, tellurites, and telluriates.
SECTION III. -SALTS OF THE COMPOUND ACID-RADICALS
WHICH CONTAIN OXYGEN AND SULPHUR COMBINED WITH METALS. The aluminates, chromites, chromates, perchromates, ferrites, ferrates, manganates, permanganates, bismuthates, stannates, metastannates, platinates, rhodiates, rutheniates, iridiates, osmites, osmiates, aurates, tungstites, tungstates, molybdates, vanadites, and vanadiates; the sulphostannates, sulphoplatinates, sulphorhodiates, sulphorutheniates, sulphiridiates, sulphosmiates, sulphaurates, sulphotungstates, sulphomolybdates, and sulphovanadiates.
SECTION I.—The oxides, sulphides, selenides, and tellurides. SALTS OF OXYGEN, SULPHUR, SELENIUM, AND TELLURIUM.
We have already seen that these four acid-radicals are bibasic, and that the following formulæ are some of those which belong to the various combinations of metals with oxygen—(M,0, M,0, (M),0, M,0,, M,O, M,05,—while, besides these common oxides, which can exist in the isolated condition, there are many others which play the part of acid-radicals, and are only known to us in combination with a basic constituent: such compounds are represented by the following formulæ among others :—MO, MO,, MO,, MO, M, O,, M, 0,, &c. And in addition to these hypothetical compounds of metals with oxygen, there are numerous existing combinations of oxygen with other acid-radicals. What has been here said concerning oxygen, is true also as regards sulphur, and to a great extent with reference to selenium and tellurium.
In common with other polybasic radicals, the members of the present subdivision possess the power of combining with, and uniting in one salt, separate single equivalents of two different basic radicals; and although, in the class before us, one of these basic bodies is invariably hydrogen, yet, in salts containing more complex acid-radicals, two different metals are frequently combined with one and the same equivalent of acid-radical. The hydrates and sulphydrates already mentioned are salts in which this peculiarity occurs (1 eq. of hydrogen and 1 eq. of metal are united with a single equivalent of the biatomic radical oxygen); and they are comparable with the oxides and sulphides, in which 2 eqs, of metal are united with a single equivalent of the biatomic radical: Oxides. Hydrates.
The salts of the present subdivision may be recognized by the employment of the same means that are used for the detection of the members of the preceding subdivision : i.e., 1st, by the formation of insoluble compounds ; 2nd, by their decomposition, and the subsequent recognition of their acid-element.
. SALTS OF OXYGEN, OR OXIDES. There are very many oxides known; as a general rule they may be regarded as very stable salts. Many oxides are of brilliant colours; some are white. Several of the oxides which occur in nature, and also of those which have been fused or crystallized, possess a metallic lustre.
Oxides, when heated upon charcoal, are frequently reduced to the metallic state; some, indeed, are thus decomposed by heat alone, others by the joint action of heat and of the affinity, for the oxygen of the salt, which the carbon exerts. There are oxides, however, which can be decomposed only by the most powerful chemical agencies. The various blowpipe reactions of the metallic oxides have been already described under their respective metals.
THE HYDRATE OF HYDROGEN (HHO), hydric acid, or water, is a body too well known to need description : it plays the part of an acid, exchanging 1 eq. of hydrogen, under suitable conditions, for an equivalent of a different basic radical; but so nicely are the opposing properties of its constituents balanced, that it is a very stable body, and is quite neutral with reference to a great many salts. This neutrality, combined with its vast solvent power on solids, liquids, and gases, renders water of the utmost service in chemical operations; and in this capacity of a solvent it cannot be replaced by any known substance. The presence of water in certain salts as water of crystallization or of hydration is little understood; but perhaps it is connected in some way with this neutrality of which we have been speaking.
There is no oxide known which is soluble in water without decomposition; for all the oxides upon which water seems to exert a solvent action are in fact decomposed by it. When water is
viewed as hydric acid, this change becomes intelligible; with oxide of potassium it may be represented thus
KKO+HHO-KHO+KHO. Water, indeed, may be regarded as the normal oxide of hydrogen, but, being itself the universal solvent, cannot be regarded as soluble.
The presence of oxygen cannot be well ascertained by double decompositions in which oxides and hydrates are precipitated ; it is always preferable to employ other means. Those methods which are admissible are of two kinds : in one we prove the absence of all other salt-radicals except oxygen ; and in the other we detect the oxygen by the decomposition of the salt under examination.
For the sake of comparison with the salts of other acid-radicals, we give a few of the more important insoluble oxides and hydrates, produced by the action of a solution of hydrate of potassium on the different metallic solutions, neither reagent being in excess.
TAE POTASSIUM, Sodium, and AMMONIUM Salts (hydrates) are very soluble in water.
THE BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM SALTS (hydrates) are somewhat sparingly soluble.
THE CUPROUS Salt ([Cu,],0) is orange-yellow. It is soluble in most acids.
THE CUPRIC SALT (CuHO) is blue. It is soluble in hydrate of ammonium, and in most acids.
THE SILVER SALT (Ag, O) is brown. It is soluble in hydrate of ammonium, and in most acids.
THE MERCUROUS SALT ([Hg,],0) is brownish black. It is soluble in most acids.
THE MERCURIC Salt (HgHO, H,O) is yellow. It is soluble in most acids.
THE LEAD SALT (Pb, HO,) is white. It is soluble in most acids.
The other oxides and hydrates have been already described under their respective metals in Chapter VI.