and pungent odour. Upon a similar formation of an odorous and volatile body depends, in great measure, the recognition of the presence of the acetic acid-radical. To the substance supposed to be or contain an acetate, sulphuric acid and alcohol (C, H, HO) are added, and the mixture heated. The former reagent will produce, with an acetate, acetic acid (i. e. acetate of hydrogen) (HC, H, O2 or HA); and this, acting in the nascent state on the alcohol or hydrate of ethyle (C, H, HO, or EHO), yields a fragrant body, the acetate of ethyle, thus

The acetate of ethyle, or acetic ether, is volatilized at the temperature employed, and, possessing a most peculiar and agreeable fruity odour, is easily identified.

We will now consider briefly the second method of detecting acid-radicals, by the actual elimination of the acid-radical itself, and the subsequent identification of its peculiar properties. And here it must be borne in mind, that a great distinction must necessarily exist between the behaviour of the acid- and basic radicals, simply on account of their inherent nature. The basic radicals with which the student has been made acquainted, and which occur in great abundance, are (with a few exceptions) elements, and, moreover, they are all (ammonium, mercury, and hydrogen only excepted) solid at the ordinary temperature. On the other hand, however, more than half of the acid-radicals of common occurrence, and almost all the rarer ones, are compound bodies, which are characterized by great diversity of physical condition, several being gaseous, some liquid, and others solid. The fact of a body being compound frequently adds to our facilities of recognizing it; for, in addition to any peculiarities which it may exhibit as a compound, we have other clues to its presence in the characteristic properties which its constituents may individually manifest when, by its decomposition, they have been set free. In fact, those acid-radicals which are complex cannot, with but few exceptions, be obtained in the isolated condition, but are resolved either into other and generally simpler compounds, or into their elementary constituents. Whilst, therefore, we indubitably prove the presence of an elementary acid-radical by

obtaining it in the free state and examining its properties, we no less distinctly show the existence of a compound acid-radical when we observe some of the well-ascertained features of the decomposition which it undergoes when liberated.

To illustrate the foregoing cases, we will take two examples. When chlorine acts upon a bromide, decomposition ensues, with separation of the element bromine, the peculiar features of which, such as the yellow colour which it imparts to a solvent, or the orange tint which starch-paper exposed to its vapour assumes, or its peculiar suffocating odour, may be immediately recognized

MBr+Cl=MCI+Br.

But if, on the other hand, we deal not with an elementary, but with a compound acid-radical, such as that existing in the oxalates, by treating the salt in such a manner as to decompose it into new and characteristic products, the latter frequently furnish us with good proof of the previous existence of the compound acid-radical. These products, in the case of the oxalates, are the two gases carbonic anhydride (CO2) and carbonic oxide (CO); and they are obtained by the action of sulphuric acid upon oxalates, the decomposition being aided by heat, thus

M.CO+2H, SO, M, SO+H, SO, HO+CO2+CO.
hydrate of sulphuric
acid.

The more easily recognizable gaseous product, or at least the more characteristic, is carbonic oxide (CO), which, when the carbonic anhydride (CO2) has been removed by an appropriate agent, may be readily kindled on the application of a light, burning with a blue flame.

The preceding hints will perhaps suffice to show the general principles upon which the detection of acid-radicals is based, and to exhibit the chief points in which their reactions resemble, and also those in which they differ from the reactions of the basic radicals. We now proceed to detail these reactions, adopting the subdivisions which have already been chosen in the description of the acid elements. The classification of the acid-radicals is thus entirely founded upon the chemical characters of each group, and not upon their similarity in an analytical point of view. 1. Salts containing the acid-radicals of Subdivision I. (page 17). SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE, AND of

THE CHIEF COMPOUND ACID-RADICALS INTO THE COMPOSITION
OF WHICH THEY ENTER.

2. Salts containing the acid-radicals of Subdivision II. (p. 18). SALTS OF OXYGEN, SULPHUR, SELENIUM, AND TELLURIUM, AND

OF THE CHIEF COMPOUND ACID-RADICALS INTO THE COMPOSI-
TION OF WHICH THEY ENTER.

3. Salts containing the acid-radicals of Subdivision III. (p. 18).

SALTS OF CARBON, BORON, SILICON, TANTALUM, NIOBIUM,
PELOPIUM, AND TITANIUM, AND OF THE CHIEF COMPOUND

ACID-RADICALS INTO THE COMPOSITION OF WHICH THEY ENTER.

4. Salts containing the acid-radicals of Subdivision IV. (p. 18).

SALTS OF NITROGEN, PHOSPHORUS, ARSENIC, AND ANTIMONY,

AND OF THE COMPOUND ACID-RADICALS INTO THE COMPOSITION
OF WHICH THEY ENTER.

SUBDIVISION I.

SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE, AND OF THE CHIEF COMPOUND ACID-RADICALS INTO THE COMPOSITION OF WHICH THEY ENTER.

The three first-named members of this Subdivision present the most striking resemblance to each other, both in the salts which they form by simple union with the basic radicals, and also in those in which they exist as a part only of a compound acidradical. Fluorine differs in many respects, and in none more decisively than in not forming compound acid-radicals similar to those which the other members of the group are known to yield. In the further arrangement of the present Subdivision, as also in the arrangement of those which follow, we take advantage of the differing chemical constitution of the members, and not of any analytical characteristics which they may present. In accordance with this plan, we now proceed to divide the present group into three Sections, as follows:—

SECTION I-SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE.

The chlorides, bromides, iodides, and fluorides.

SECTION II.-SALTS OF THE ACID-RADICALS WHICH CONTAIN CHLORINE, BROMINE, AND IODINE COMBINED WITH OXYGEN.

The hypochlorites, chlorites, chlorates, perchlorates, hypobromites, bromates, iodites, iodates, and periodates.

SECTION III.-SALTS OF THE ACID-RADICALS WHICH CONTAIN CHLORINE, BROMINE, AND IODINE COMBINED WITH METALS.

The chloropalladiates, chloroplatinates, chlororhodiates, chlororutheniates, chloriridiates, and chloraurates.

SECTION I.-The chlorides, bromides, iodides, and fluorides. SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE. The radicals of this Section are monobasic, and when combining with monatomic basic radicals yield compounds having the general formula MR. They are detected by both the methods described in the preliminary observations to the present Chapter, i. e. both by presenting to a soluble chloride, bromide, iodide, or fluoride a soluble salt of some basic radical known to form, with the acid element sought for, an insoluble salt of easily recognizable properties, and also by submitting the chloride, bromide, or iodide to such decomposing influences as are calculated to eliminate their acid-radical.

SALTS OF CHLORINE, OR CHLORIDES.

These salts are for the most part soluble in water, sparingly soluble in alcohol, and nearly insoluble in ether. Their formulæ vary according to the atomic nature of the combined basic constituent; but the following are the most usual:

MC1, MC1, M,Cl,, MC12, and MC1,.

When heated before the blowpipe on charcoal, the deportment

of chlorides differs according to the nature of the combined basic radical: if the metal belongs to Subdivision I., the compound fuses, and sinks into the charcoal; if to Subdivision II., it fuses and generally remains as a molten mass upon the charcoal: the chloride of magnesium is the exception here; for, as it cannot exist in the presence of aqueous vapour, it suffers decomposition, and leaves a white residue of oxide. Some of the remaining chlorides, such as those of silver and lead, fuse without change; others again, as those of tin, antimony, and arsenic, volatilize, whilst others, such as those of platinum and gold, decompose into chlorine and the metal.

If a bead of microcosmic salt be fused upon a platinum wire, and cupric oxide (Cu,O) added to it until the bead is saturated, if a chloride be then introduced, and the bead submitted to the heat of the blowpipe jet, a blue colour will be imparted to the flame.

THE HYDROGEN SALT (HCl), or hydrochloric acid, is a transparent colourless gas at ordinary temperatures, which, at 45°3 C., and under the pressure of 40 atmospheres, becomes a colourless liquid, highly dispersive of light. 1 volume of water dissolves 480 volumes of the gas.

The principal insoluble salts of this acid-radical are-as the student will readily recollect-the cuprous, argentic, plumbic, mercurous, and platinous chlorides.

THE CUPROUS SALT is produced by the action of a soluble cupric salt on a solution of stannous chloride. Its formula is Cu,Cl. It is insoluble in water, but soluble in most acids.

The Argentic or Silver Salt is produced by the action of a soluble silver salt on hydrochloric acid or any other soluble chloride: it is a white curdy precipitate, which assumes a grey tinge on exposure to light.

Its formula is AgCl.

It is insoluble in water, soluble to a slight extent in solutions of certain chlorides and in concentrated acids, and easily dissolves in hydrate of ammonium, in cyanide of potassium, and in hyposulphite of sodium.

THE MERCUROUS SALT is produced by the action of a soluble