hydrogen may be retained in a state of union, each possessing its specific form, and the substance which results possesses very interesting properties. It consists of two particles of oxygen, one on each pole of a particle of hydrogen (Fig. 39): hence, as has been already shown, it must possess the property of discharging colours. It also disorganizes the skin, and thickens the saliva. It is a limpid liquid of very difficult congelation, and, at the temperature of 15° cent. or 60° Fahr., resolves itself into water and vital air. It is very interesting to observe, that, though it contains already an excess of oxygen, it may become a deoxidizing agent, a fact inexplicable in any other view of the structure of oxygen, than that here given. When presented to loosely engaged oxygen, such as that in the oxides of the noble metals, the same phenomena ensue as if they were exposed to a stream of hydrogen gas. The oxygen of the deutoxide, in its intermediate state between that of oxygen and water, is attracted to the contiguous oxygen, and separated as particles of hydrogen. Thus, water is formed by the aid of the oxygen of the oxide, in sets of five particles for every particle of oxygen in the deutoxide whose conversion into hydrogen takes place. It is to be remarked, that a particle of this substance is that which would result, were a molecule of vital air to be reversed, and the two atoms of radiant. matter to unite. It is not impossible, then, that it may be generated in a sunbeam; and to this partly, perhaps, and in some instances, the solar ray may owe its bleaching properties. Deutoxide of hydrogen has been very rarely produced in the laboratory; it owes its discovery to the genius of M. Thenard. The phenomena which it exhibits are perfectly inexplicable on the common chemical hypotheses.

It has been already shewn, that when oxygen and hydrogen are placed in each other's vicinity, and in a state of natural electrical equilibrium, water is immediately formed. The

decomposition of water on the great scale, is therefore difficult, for the nascent gases, immediately when removed from the decomposing focus, unite again and reproduce water. Hence there might be very powerful decompositions of water into oxygen and hydrogen, at depths of the ocean, and no elastic matter escape at the surface, were water subject only to decomposition into oxygen and hydrogen. For preserving the oxygen which has been developed, it is necessary that both its poles be covered, and the access of hydrogen prevented.

Now, if we consider the structure of a particle of water, we must expect, that, though it be chiefly decomposed into oxygen and hydrogen, another form may frequently result from the five particles of hydrogen left by the departure of the sixth. Such, indeed, must always be the case when a particle of hydrogen is driven out from the centre of the particle of water. But other accidents, such as an aversion in the medium to the development of negative forms, may produce the evolution of the same form, which is much less negative than oxygen. Suppose, by a violent compression in the direction of the equator, that a particle of hydrogen is driven in towards the centre, its presence there forms a mechanical obstacle to the evolution of the form of oxygen, and the five remaining particles are under the necessity of uniting by their apices, and a form (Fig. 12) results, possessing symmetry enough to exist for some time. This is a particle of nitrogen.

To become symmetrical, this body must either disengage the five atoms of matter which project from one side, so as to give rise to the form (Fig. 4), or provide itself with other five to the other side, so as to give rise to the form (Fig. 7). We may suppose that one will do the first, and another contiguous serve itself with the atoms which the first has set free, and thus from two of the unsymmetrical forms (Fig. 12), there result two symmetrical ones, (Figs. 4 and 7). But should two of the unsymmetrical bodies (Fig. 12.) meet, it is evident that they can unite together, and a beautiful, highly symmetrical, and quiescent form, results (Fig. 14). Such are the forms, together with oxygen and hydrogen, which are most

immediately derived from the decomposition of water; and that such decomposition must take place abundantly in the ocean, both on its confines with its own basin and the sunbeam, we can scarcely doubt.

The two small forms (Figs. 4 and 7), as will be afterwards shewn, continue in the ocean, but the large symmetrical one (Fig. 14) is aëriform; it is evident that its poles are conformable to those of oxygen; and if two such contain a particle of oxygen between them (Fig. 40), it will be secure from the access of hydrogen, and the whole may emerge at the surface. Its axis, however, where a more advantageous union is afforded to the oxygen, will subdivide, and, at the surface, each molecule will separate into three parts, from which will result one particle of vital air, (now occupying the centre as oxygen), and two molecules of nitrogen, or one binate molecule, or volume of vital air, and four of nitrogen. Now, this is the known. composition of the atmosphere.

We are thus introduced to another body composed of hydrogen, which, though itself is somewhat inert and uninteresting; yet consists of two particles locked up, which, individually presented to other bodies, possess very great chemical activity. The atomic weight of a particle of nitrogen is 10. It is, therefore, five times the atomic weight of hydrogen, and this has been already assigned as its atomic weight by Dalton. Its specific heat must be considerable, but, like oxygen, its properties are unknown, as its particles instantly on the nascent state, unite face to face, and constitute a molecule of nitrogen, whose atomic weight is consequently 20, or double that of a particle.

The gas composed of binate molecules of nitrogen is invisible and tasteless. Its specific heat is said to be rather

• The atomic weights of nitrogen by Berzelius, Wollaston, and Thomson, when transferred from vital air considered as 10 to oxygen, and thus made to correspond to the atomic ratios of this work, gives,

Berzelius, 9.750

Wollaston, 9.645

Thomson,

X 2.

9.625

True weight, 10.000

greater than that of vital air, as we should expect; its magnitude is nearly the same as a molecule of vital air; its atomic refractive power is considerably greater. The specific gravity and weight of 100 cubic inches must, consequently, be less than that of the same volume of oxygen (vital air deprived of radiant matter); and, accordingly, instead of 1.010, or that of oxygen, the specific gravity of nitrogen is found to be about 972; and, therefore, instead of about 31 grains to 100 inches, that volume of nitrogen is found to weigh about 29.76 grains. But, when we consider that no two chemists. ever found a volume of the same gas to possess the same weight, we will almost cease to be curious about small fractions of grains. In this gas, indeed, the weights assigned are very uniform; and, besides, nitrogen, common air, carbonic oxide, and carbonic acid, ought to give uniform results, in as far as their own structure is concerned; but when the action of the gas upon the radiant medium is considerable, as in the case of the compounds of carbon, sulphur, phosphorus, and chlorine, with hydrogen, the weights are very variable at different times and places, and in the hands of different manipulators.

Nitrogen is not only developed in the inorganic kingdom by the decomposition of water; it is an abundant product of animal assimilation. While it remains in the organization of animals, however, there is every reason to believe that it exists in a solid state, or as an icosaedron (Fig. 13); and if so, the icosaedron may be regarded as the characteristic form of the animal structure, as the decaedron (Fig. 4), afterwards to be illustrated, is of the vegetable. Carnivorous animals receive it into their bodies as an ingredient in their food, but a greater quantity is found in the blood of the ox than in that of man, though the former is not known to consume any nitrogen at all. It is true, that, at every respiration, a large quantity descends by the windpipe, though not the gullet; but whether absorption take place in the lungs or not, there is positive evidence, that as much, or more, nitrogen is given out, than is inhaled. In these organs, indeed, the assimila

tion of water, or its equivalent hydrogen, into nitrogen, is somewhat distinctly intimated. The lungs are, by their natural organization, conformed to a mixture of vital air and nitrogen; and when this natural state is destroyed, their action tends to restore it. Thus, Messrs Allen and Pepys confined a guinea-pig in an atmosphere of vital air, and the residuary atmosphere was found to contain a volume of nitrogen larger than the animal's own body. In another experiment, they confined it in an atmosphere composed of 21 parts vital air, and 79 hydrogen: the result was the same as before, but the appearance of the nitrogen was accompanied with the disappearance of a quantity of the hydrogen. It is never safe to judge of the healthy functions of an organ, by placing it in circumstances where a diseased or unnatural action is demanded; but all experiments are adverse to the opinion, that any quantity of the nitrogen, so abundant in animal bodies, can be derived from the air. The experiments of Dr Edwards even prove, that animals give out more than they inhale, and that chiefly at the fattening time of the year, as if an excess generated from the food eaten, found an exit from the lungs in a manner analogous to carbon. The growth of fishes is sometimes amazingly rapid, while their respiration is very inconsiderable.

These facts, and others afterwards to be mentioned, connected with the voltaic decomposition of ammonia, have induced some chemists to regard nitrogen as a more compound body than oxygen; but under the electric discharge it suffers no more change than the other. Indeed, we should expect that hydrogen and nitrogen are the two gases into which others should be resolved in such a process, rather than that they should suffer change; and perhaps means may yet be discovered for converting oxygen and nitrogen into each other. There seems no reason why an electric shock, which is chiefly transmitted along the radiant medium, should injure either of them. But time, and the sunbeam made to act upon bodies in certain unnatural electrical states sustained during the whole experiment, might probably effect many of those changes