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A MANUAL OF CHEMICAL ANALYSIS
PART I.—CHEMICAL REACTIONS.
INTRODUCTION. TERRESTRIAL matter has been found by the researches of chemists to be capable of resolution into about sixty-two elements or simple bodies; of these nearly half are of frequent occurrence, while the remainder are comparatively rare. Thus every substance met with in nature is either an element or a combination containing two or more elementary bodies, either mechanically or chemically blended. When it is desired to ascertain what simple bodies exist in any given form of matter, chemical analysis is resorted to.
The student who seeks to become fitted for this method of inquiry, should investigate carefully the chemical properties of the simple substances, since it is only by observations founded upon them that he will be able to distinguish the various constituents of the bodies that may be presented to him for examination.
Investigation into the chemical properties of the elements has shown that many of them are diametrically opposed to one another, and thus two great classes may be formed, characterized by the possession of most antagonistic properties : to one of the classes the term “basic elements” has been applied, and to the other that of “acid elements.” These classes have also been named “metals” and “ metalloids” respectively, as well as “electro-negative” and “ electro-positive" elements. Attempts, however, at absolute classification fail, since it is found that some of the simple bodies occupy an intermediate position, and, strictly belonging to neither division, serve to connect the extremes to
gether. To place them therefore somewhat in the form of an arc, is preferable to arranging them in two columns under distinct heads. Potassium (K) thus commences the list of basic elements, and chlorine (Cl) begins that of the acid elements; while the elements connecting the lower ends of the scales partake, to some extent, and in certain circumstances, both of the basic and acid character.
Notwithstanding its want of strict correctness, a more arbitrary and absolute di vision into basic and acid elements is a very convenient one for analytical purposes; and in accordance with this classification, we will now proceed to consider the chemical properties of matter.
THE BASIC ELEMENTS. THE bodies which constitute this class are those elements known by the name of metals, together with the gas hydrogen. The metals are for the most part solid bodies, although one, mercury, is liquid, and thus forms a link between the solid basic elements and the gaseous one, hydrogen. From its close resemblance to the other basic elements, this gas also is expected, if ever sufficiently condensed, to appear in the metallic form. The metals are characterized by peculiar physical properties, the chief of which are “metallic” lustre, and power of conducting heat and electricity; but the first of these properties, although frequently quoted as an unmistakeable proof of the metallic character of a body, is so dependent upon the state of aggregation of its particles, being entirely lost if the metal is reduced to a fine powder, as to be of little value; while the power of conducting electricity and heat is to be considered but doubtful evidence of metallic character. Chemical characteristics are the best criteria of the basic nature of a body; that is to say, it must possess properties powerfully opposed to those of the acid elements.
The great class of basic elements may be thus subdivided :
1. Metals which are lighter than water (H,0), and decompose it at common temperatures :
Potassium=K. Sodium=Na. Lithium=Li.
2. Metals which are heavier than water (H,O), and decompose it at common temperatures :
Barium=Ba. Strontium=Sr. Calcium=Ca. Magnesium=Mg.
3. Metals, the majority of which expel hydrogen (H) from hydrochloric acid (HCl) at common or boiling temperatures :
SUBDIVISION I. POTASSIUM, SODIUM, AND LITHIUM. These metals possess a silvery lustre ; they are of less specific gravity than water. They are very difficult of preparation, on account of their great affinity for oxygen, with which they are often found combined in nature. A bright surface of any one of these metals becomes immediately tarnished if exposed for a moment to the air, a combination with the atmospheric oxygen being effected. Under the influence of the same affinity they decompose water, which is a chemical compound of oxygen and hydrogen, combining with its oxygen and setting free its hydrogen..
I. POTASSIUM=K. Potassium may be readily recognized by placing a small portion of it on the surface of water; the water is decomposed by the potassium, which becomes red-hot (a circumstance of frequent occurrence in chemical actions); the evolved hydrogen is then set on fire by the heated potassium, and burns with a violet flame, the colour being due to the presence of a small quantity of vaporized metal. Owing to its great tendency to combine with oxygen, potassium is always preserved under some liquid which contains none of that element: the liquid generally employed is Persian naphtha.