ITS SEPARATION FROM AMMONIA BY CHLORINE.

33

chemists term Nitrogen, is marked rather by the absence of salient characteristics than by any active properties of its own. Even its volume-weight is, so to speak, of a neutral average character. While hydrogen is very much lighter, chlorine very much heavier, and even oxygen somewhat heavier than air, we find the volume-weight of nitrogen and air to be almost identical. Compared with hydrogen as a standard unit, the volume-weight of nitrogen is 14, that of air being 14.4, as already stated. This will not, however, be matter of surprise hereafter; when, studying in its turn the composition of atmospheric air, we find nitrogen to be its most abundant constituent.

Nitrogen may be liberated from ammonia by a process similar to that which enabled us to separate oxygen from water, namely, by the action of chlorine. Even at common temperatures chlorine combines with the hydrogen of ammonia, and sets free its nitrogen. For this purpose we pass a current of chlorine gas through the strongest ammonia-solution of commerce contained in a large three-necked bottle (Fig. 42). Powerful action

is at once manifested by the formation of white fumes in the upper part of the bottle, while flashes of light traverse the

34 HYDROGEN AND NITROGEN SOLE CONSTITUENTS OF AMMONIA.

liquid, which is caused to effervesce by the evolution of gas. The white fumes evolved indicate the formation of a solid body, with which we are not at present concerned, further than to mention that it necessitates the use of the wide connecting tubes shown in the figure, as small ones would be speedily choked by the condensation of the fumes. The gas obtained is passed through a wash-bottle, and then collected over water for examination; which soon proves it to be neither hydrogen nor chlorine nor oxygen, but the same gas (nitrogen) which we obtained by the electrolysis of ammonia.

By means of the electric current, we have analytically proved hydrogen and nitrogen to be constituents of ammonia. The presence of these two gases in ammonia has been, moreover, demonstrated; that of hydrogen by the action of sodium, that of nitrogen by the aetion of chlorine. To proceed in accordance with the plan adopted in the examination of hydrochloric acid and water, we should now by synthesis prove hydrogen and nitrogen to be the only constituents of ammonia. Unfortunately, up to this hour no simple process has been discovered whereby ammonia can directly be reproduced from hydrogen and nitrogen. We must, therefore, for the present rest contented with the fact that the united weights of hydrogen and nitrogen extracted from ammonia have been found to correspond exactly with the weight of the ammonia operated on-a result affording irrefragable proof that these two bodies, and no others, enter into the constitution of ammonia.

The study of hydrochloric acid, water, and ammonia, has acquainted us with a series of facts, the importance of which will not be fully apparent to us till we are further advanced in our inquiry. But we have already obtained some partial insight into the wide field of research they open up; and a brief retrospective glance may be appropriate here to prepare us for proceeding with our investigation.

Under the influence of electricity, of heat, and of certain chemical agents, we have seen a small number of well-known

ELEMENTARY BODIES; THEIR CHARACTERS.

35

substances pass through a series of most remarkable transformations. By appropriate treatment, hydrochloric acid has been found to split up into hydrogen and chlorine, water into hydrogen and oxygen, ammonia, lastly, into hydrogen and nitrogen.

The ingredients, thus dissevered, we have found ourselves able, in the case of hydrochloric acid and water, directly to recombine, so as to call again into existence the compounds we had previously decomposed; and though, in the case of ammonia, direct synthesis proved to be impossible, chemists have ascertained, by means of the balance, the precise weight of each constituent entering into the composition of a weighed quantity of the compound. In this manner, by a twofold demonstration the most cogent that can be conceived, hydrogen and chlorine, hydrogen and oxygen, hydrogen and nitrogen, have been proved to be the true and only constituents, respectively, of hydrochloric acid, water, and ammonia.

Having thus succeeded in determining the constituents of hydrochloric acid, water, and ammonia, we are naturally led to inquire into the characters and composition of those constituents themselves.

Is it in our power to resolve hydrogen, chlorine, oxygen, and nitrogen into simpler forms of matter? and, if so, what are the methods of analysis by which this result may be achieved?

To these questions, which have been experimentally propounded to Nature by many of the most illustrious philosophers, as well of the present as of past generations, but one answer has been obtained, viz., that hydrogen, chlorine, oxygen, and nitrogen, are incapable of decomposition by any means as yet at our disposal. They resist the powerful influences of electricity and of heat, even when raised to the highest attainable degrees of intensity; and they issue unchanged from every variety and form of chemical reaction hitherto devised in the hope of resolving them into simpler forms of matter. are therefore justified in regarding hydrogen, chlorine, oxygen, and nitrogen as indecomposable, or simple bodies, termed

We

36

NUMBER AND CLASSIFICATION OF THE ELEMENTS.

ELEMENTS, in contradistinction to compound, decomposable bodies, such as hydrochloric acid, water, and ammonia.

How many of these bodies, simple and compound, are there ? Of compound bodies, we find a series, numbering many thousands, in the so-called inorganic kingdom of nature, which comprises all the diversified mineral constituents of our earth's crust; while another series, far more complex in composition, and almost innumerable in multitude, exists in the two great provinces, vegetal and animal, which together make up Nature's organic realm. Yet all this boundless variety of matter springs from only 61 primary bodies, or elements, diversely combined. These appear to be the constituents of the celestial bodies, as well as of our earth. The meteorites which at intervals reach our planet from the sky are built up of no other ingredients; and, as a bold but well-founded induction has, of late years, justified the belief that several of them are also constituents of the sun and other fixed stars, we are entitled to regard it as possible that many, if not all, of the remainder may also exist in those bodies.

These 61 elements are arranged alphabetically in the following table, in which, it will be observed, they are classified in three groups, by the use of types of three degrees of prominence. The first group, distinguished by the largest type, comprises, besides the four elements with which we have become acquainted in these introductory sketches, some 14 more, which may rank with them as the 18 most widely diffused bodies found at the surface of our globe. This class includes the main constituents of the Ocean (oxygen and hydrogen), of the Atmosphere (oxygen and nitrogen), and of the Earth's crust (oxygen in combination with silicon, carbon, and the metallic constituents of the earths and alkalis). With these are also classified others which, like bromine and iodine for example, though much less abundant, are equally pervasive. Next in typographical prominence are ranged some 23 elements, comparatively rare, but all more or less useful in the arts, and many of them, such as copper, tin, zinc, &c. familiar to us in every-day life. A third

TABLE OF THE ELEMENTS.

37

series, distinguised by the smallest type, comprises about 20 elements, which may be termed Nature's chemical raritiesbodies occurring so seldom, and in quantities so minute, as to baffle our endeavours to trace the service which they may render, either in the household of nature or in the arts of life. In this group, three other supposed elementary bodies (Erbium, Terbium, and Norium), would find their appropriate places, had not recent researches shown their existence to be so problematic, as to render them quite inadmissible in a list of established elements.

The typography of this table makes it apparent at a glance that only about one-third of the elements are entitled to rank as of primary, and a somewhat similar number as of secondary importance. It is to these two classes of elements, of course, that our attention will be principally directed. On the "chemical rarities" we shall bestow but a cursory glance.

From the manner in which we have arrived at the idea of element, it is obvious that this term must be used with certain restrictions. The bodies enumerated in the above table we