Page images
PDF
EPUB

rendered it apparent that, from the extremely energetic properties which have been impressed upon these classes of elementary matter, it must be a comparatively rare occurrence to find them existing in nature in the isolated or uncombined condition; and therefore, if we are provided with no other means of recognizing them than those which apply to that state, these bodies must frequently elude us. Such means are not, however, wanting; and it will be seen from the observations which follow, and from the details which will occupy this and the next chapter, that the tests which we can apply to prove the existence of these bodies in their compounds, are, if possible, still more copious and conclusive than those which serve to assure us of their presence when they exist in the elementary state.

In the present chapter we shall devote ourselves exclusively to the detection of the basic radicals in their compounds; reserving the description of the methods of distinguishing the acid radicals of compound bodies for a subsequent chapter.

The principal means at our disposal for the recognition of a basic radical, is by the addition of some reagent to produce a saline combination which shall contain it, and which shall be at the same time easily identified by some remarkable physical or chemical characters. The majority of those compounds, the formation of which is held to be most conclusive proof of the presence of a basic radical, are such as present some striking peculiarity of colour, or of insolubility in certain menstrua, or of colour and insolubility combined ; but there are others again which are gases of well-marked properties ; and these are equally recognizable, and no less certain criteria of the presence of the body sought for.

The great mass of the basic radicals with which the student will have to do being elementary, no proof can be obtained of their presence from any decompositions which they might undergo; the compound basic radicals, as ammonium, strychnine, morphine, and quinine, being of complex constitution, may be thus recognized.

Without further remark we will now proceed to state at length the various tests for the basic radicals when in combination, pausing only to give a synoptical view of the subdivisions to be adopted, the members of each of which will be found identical with those given at page 3, as the subdivisions of the basic elements. In Subdivision III., however, three organic bases have been introduced.

1. Salts, the solutions of which are not precipitated by carbonate of ammonium; by a mixture of the chloride, hydrate, and sulphide of ammonium; or by the passage of hydrosulphuric acid gas through their acid solution :

SALTS OF POTASSIUM, SODIUM, LITHIUM, AND AMMONIUM.

2. Salts, the solutions of which are precipitated by carbonate of ammonium ; but not by a mixture of chloride, hydrate and sulphide of ammonium, nor by the passage of hydrosulphuric acid gas through their acid solution :

SALTS OF BARIUM, STRONTIUM, CALCIUM, AND MAGNESIUM.

3. Salts, the solutions of which are precipitated by carbonate of ammonium, and also by a mixture of chloride, hydrate and sulphide of ammonium; but not by the passage of hydrosulphuric acid gas through their acid solution :

SALTS OF YTTRIUM, ERBIUM, TERBIUM, THORINUM, CERIUM,

LANTHANIUM, DIDYMIUM, ZIRCONIUM, GLUCINUM, ALUMI-
NIUM, CHROMIUM, URANIUM, IRON, MANGANESE, COBALT,

NICKEL, ZINC, MORPHINE, QUININE, STRYCHNINE. 4. Salts, the solutions of some of which are precipitated by carbonate of ammonium, and by a mixture of chloride, hydrate and sulphide of ammonium ; but all of which, without exception, are precipitated by the passage of hydrosulphuric acid gas through their acid solution :

SALTS OF CADMIUM, COPPER, SILVER, MERCURY, LEAD, BIS

MUTH, PALLADIUM, TIN, ANTIMONY, ARSENIC, PLATINUM,
RHODIUM, RUTHENIUM, IRIDIUM, OSMIUM, GOLD, TUNGSTEN,
MOLYBDENUM, VANADIUM.

SUBDIVISION I. SALTS OF POTASSIUM, SODIUM, LITHIUM, AND OF THE

COMPOUND METAL AMMONIUM. The number of these combinations is of course only limited by the number of acid-radicals in existence, each of the above basic bodies (and the same observation is true of most of the basic radicals) having the property of forming salts with every acid radical. The stability of these combinations varies with the accurate opposition of the combining substances to each other; if they are unequally matched, then a ready decomposition is effected, if a more appropriate combination can afterwards occur. Since the metals of this subdivision are the most powerfully basic bodies with which we are acquainted, the inequality of power, if there be any, is always on the side of the acid-radical, and such compounds are invariably decomposed when brought into contact with an acid-radical of more intense properties. The metallic chlorides (MCI), bromides (MBr), iodides (MI), and sulphates (M, SO.) are among the more stable; while the nitrates (MNO), oxides (M,0), sulphides (M, S), hydrates (MHO), sulphydrates (MHS), and carbonates (M, CO3), are examples of the more easily decomposable salts of these metals. The decompositions take place as follows:

M0 +2HCl =8,0 +2MCI
M,CO+H,80,=H,CO, +M, SO,

MHO + HBr =1,0 +MBr. These observations also apply to the corresponding salts of almost every basic radical known.

The salts of the metals of this group are remarkable for their great solubility in water; and especially is it to be noted that their oxides, sulphides, carbonates *, sulphates, oxalates, and phosphates are soluble in that menstruum. The application of this statement will be seen when the salts of the other metals are considered, since many of their combinations with the acid radicals mentioned above are insoluble in water.

* The rare metal lithium presents a remarkable exception here, its carbonate and phosphate being insoluble.

There are certain conventional expressions applied to the salts of this group with which the student should familiarize himself :

1. Their hydrates (MHO) are termed “the alkalies,” or “ the caustic alkalies ;" and the hydrates of potassium and sodium are called “ the fixed caustic alkalies,” in contradistinction to the hydrate of ammonium, which is very volatile.

2. Their salts in general are called “ salts of the alkalies," or “alkaline salts ;” and such expressions as “the sulphates of the alkalies,” or “ an alkaline acetate,” are frequently employed.

There is a very striking family resemblance among the salts of this group of metals in many of their physical and chemical properties; many of the combinations of the different members of the group, with the same acid-radical, crystallize in the same form, or are isomorphous : they are all colourless also, unless combined with a coloured acid-radical; and in peculiarity of taste, and absence of actively poisonous properties, they possess a great similarity.

Since the great object of analysis is continually to subdivide larger into smaller groups, until at last each individual member is isolated, we will at once divide this group into two sections, by availing ourselves of the following properties of the different members :

SECTION I.-SALTS OF POTASSIUM, SODIUM, AND LITHIUM. Not volatilized by exposure in a dish to the heat of a naked flame, i. e. by ignition.

SECTION II.--SALTS OF AMMONIUM. Readily volatilized by ignition.

We have comparatively slender means at our disposal for the detection of all these metals, on account of the great solubility of most of their salts in all menstrua; for it must be remembered that our recognition of substances depends for the most part upon the formation of some insoluble salt of well-defined physical peculiarities of colour or form. The few salts which are insoluble present, however, such striking features, as almost to defy mistake.

SECTION I. Bodies not volatilized by ignition.
SALTS OF POTASSIUM, SODIUM, AND LITHIUM.

SALTS OF POTASSIUM. Solution for the reactions :-chloride of potassium (KCl) in water.

The metal potassium combines with oxygen in two proportions, forming a protoxide 1,0, and a peroxide K,0,; oxygen is, however, the only acid-radical with which potassium is known thus to combine; every other salt which it forms contains the basic and acid-radicals, either in the same relative proportion as they occur in the protoxide K,0, or in those in which they occur in the (proto-)chloride KCl, they are therefore termed protosalts; and all may be referred to the two types of MCI and M,0. The potassium salts are white, unless the acid-radical contained in them, or an associated basic radical, is coloured; they are good examples of the taste known as saline, and are not usually poisonous, unless taken in very large quantities ; they are often employed in medicine.

When heated before the blowpipe they frequently decompose, if their acid-radical is a compound; and this decomposition is the more readily effected when they are heated in the presence of some powerful chemical agent, such as charcoal, which forms the usual support for substances undergoing the blowpipe examination.

This body, although inert generally at low temperatures, becomes at high temperatures a very powerful chemical agent, and by its influence under such circumstances, a sulphate, for instance, would be converted into a sulphide, thus

K, 80, +2C=K, S+200,: or again, a nitrate would yield a carbonate by the joint effect of the heat and the carbonic acid produced by the combustion of the charcoal, thus

4KNO3 +50=2K, CO, +300, +4N.

« PreviousContinue »