by receiving an atom in its pole. But, in this case, there will evidently be no destruction of the form of the oxygen. Two such particles, each charged with an atom of radiant matter, will immediately place themselves so as to cover each other's naked poles, and constitute a symmetrical molecule, formed by two particles of vital air, as in Fig. 38.

The absolute atomic weight of a particle of vital air, then, is 11; of a molecule 22. The relations between the atomic weights of this work and those of other systems, will now be seen. According to the views of Dalton, the atomic weight of hydrogen is assumed as unity; that of vital air is regarded as 7, because this is supposed by him to be the weight of the oxygen which unites with 1 of hydrogen to form water. Sir H. Davy, not insisting upon the atomic views of Dalton, agreed with him in making hydrogen the unit; but the proportional number for oxygen he regards as 15, because a volume of vital air, equal to one of hydrogen, which weighs 1, is believed by him to weigh 15. The views of Berzelius, who, like Davy, has respect to equal volumes, are the same; but he wisely transfers the initial number from hydrogen to vital air, or oxygen, making the latter 100, and hydrogen 6.2177. Wollaston agreed with Dalton, in making the atomic weight of oxygen correspond to half a volume of the same, and this he has the happiness to make 10, while that of hydrogen he regards as 1.32. Prout reduces the ratio of these two bodies to that of 8 to 1, or 1 to 1.25, and these are the fundamental numbers of the system of Thomson. As no distinction is made by these philosophers between vital air and oxygen, the notation of Berzelius, Wollaston, Thomson, and most chemists, does not always agree with that advanced in this work. When their atomic weights are raised from the specific gravities of the bodies considered in the gaseous state, or compared with that of vital air, to be suited to those of this work, they must be increased in the ratio of 10 to 11, or multiplied by 1.1.

As it exists in the atmosphere, where it must possess its most perfect condition, the specific gravity of vital air is pro

bably rather more than 1.111; but different chemists assign different specific gravities. 100 cubic inches, were they collected and weighed, would balance about 34 grains. The most careful experiments give from 34.7 (Saussure) to 33.6 (Berzelius and Dulong). Oxygen, could it be preserved from union with radiant matter, would possess a specific gravity nearly th less, or 1.010; and the same volume would weigh, in round numbers, about 31 grains. The radiant matter in the poles of the oxygen is very free to vibrate, and will be warm, and will add something less thanth to the weight of the oxygen. The specific heat of vital air must. still be very small, though greater than that of oxygen; it gives little interruption to the transmission of light, and possesses a very small refractive or exclusive power, which might be expected from the form of its particle.

The number of molecules in a cubic inch is the same as in hydrogen; hence the number of particles is double. It might be thought that particles, such as those of vital air, so heavy compared with hydrogen, ought to be more dense under the same pressure; but their energy of mutual repulsion increases in the same ratio as their weight, for every atom added gives its repulsive as well as attractive fluid to the mass, and though differences of form might naturally produce small differences in the balancing of the two, yet the force of symmetry belonging to the surrounding radiant matter disposes their centres always to occupy the same positions, so that generally equal volumes contain an equal number of insulated particles. If an excessive repulsion or want of buoyancy render this impossible, the law of symmetry demands that the gas shall occupy every alternate cavity, or half or double the number of the first. The exceptions to this are extremely few, and occur in aëriform bodies, from which, perhaps, the radiant matter is almost entirely excluded, such as the vapour of sulphuric ether.

The electrical state of vital air is somewhat more quiescent than that of oxygen, as it has now, by the aid of the accessory atoms, acquired a positive axis. Hence its demand for union is not so vehement. Many bodies, indeed, which have

ter.

a strong affinity for oxygen, can decompose water more readily than unite with vital air; and hydrogen itself requires to be aided by a high temperature, before it can find access to the pole now occupied by the atom, and resolve the whole into waWhether this union is effected by the departure of the atom of radiant matter to give place for the hydrogen, or by an opening up of the molecule of vital air into two particles, so that the hydrogen finds its way to the naked poles before covered in, it may be difficult to determine. The latter seems more probable.

In this way, it is evident that any quantity of these gases vital air and hydrogen, if mingled in due proportions, may be wholly resolved into water, the radiant matter being disengaged; and it is no less evident, that the proportions required are an equal number of particles, or half the number of molecules of vital air, that is half the volume. During the union there is evidently a very violent movement in every particle, which generates a violent state of tremor or heat, a part of which is retained by the aqueous atom, and a part is given off to surrounding bodies. Thus, as the capacity for entertaining calorific excitement of an aqueous particle is much greater than one of oxygen, means are provided for developing it at the moment when the water, with its increased capacity, is generated. In cases of violent chemical action, luminous rays are almost always instituted in the radiant medium. It is evident that it must be thrown into a state of excitement

where the action is going on. Here, however, the light propagated is less than in many other cases, partly on account of the great heat which is adverse to lumeniferous propagation, as already shown, partly because there is no opaque body where the action is going on, to form a base to the rays of light, and render the flame visible. The most simple manner in which hydrogen and vital air may be made to exhibit their union and the resultant water, is by permitting hydrogen to escape by a small aperture into the air, and heating the matter around it by bringing a flame into it for a moment. The jet assumes a spindle form, the axis being longer or shorter according to the velocity of egress; and in the confines of this

jet with the atmosphere the union takes place. The water generated is carried up as steam by the ascending current of air, which is heated by proximity to the flame. The surface of the hydrogen burns, and this fiery stratum forms a capsule to contain it, and prevent it from dissipation in the air, till it shall have been burned by passing through.

The structure of such a flame then, is very beautiful. The internal part is hydrogen, or the combustible gas whatever it may be; then there is a stratum of burning gas, then one of water and vital air, then nitrogen, and then the atmosphere. Such an arrangement as this, where so powerful a chemical action is going on, must evidently be in a state of developed galvanism, the positive region being, as in other cases, the region of most violent action. That such is really the case, has been shewn by the researches of M. Pouillet, who found the axis of the flame negative, the peripheral region positive, and the neutral circle in some intermediate position.

Besides water, which is almost the only product of this combustion, it appears that some nitrogen is always generated, -a result which is only to be expected, as will fully appear when treating of that body.

If vital air could be compressed with sufficient violence, water would also be generated as well as by combustion with hydrogen. By the first stroke, were the atoms on the poles of all the particles brought near enough to unite in pairs, and constitute a particle of hydrogen, half the volume of vital air would condense as water. By the second stroke, which ought not to be repeated till the residuary oxygen has become provided with radiant matter again, the half would again be converted into water, and thus any quantity less than the whole of a volume of vital air, might ultimately be converted into water.

Though vital air exists abundantly in the air which we breathe, yet it cannot be directly extracted and insulated from this source, for the purposes of experiment. It is always procured from some body, in which either oxygen or vital air exists in such a state of easy combination, that it may

be disengaged by heat or a superior affinity. It is invisible, and destitute of taste and smell. Combustible bodies introduced into it when hot, burn with great vehemence, uniting with it, and degenerating into a calx or oxide, according to their species. Oxides possess no common properties. They are sometimes acid, at other times alkaline, and some are crystalline, and others aëriform. Chemical substances have received their names in a great measure from their relation to oxygen, but it is the natural use of language to name bodies from some characteristic property; and though the multitude of organized species may render generic and specific distinctions necessary in zoology and botany, yet there is not the same urgency for these refinements in chemistry. It is to be regretted that the names given by the fathers of the science are so completely forgotten; for it is not right, without some good excuse, to change a name which has been given by any one to the substance which he has discovered or first described. Nomenclature of bodies, founded upon the products of their distinction or analysis, must constantly change with the progress of the science, and, at best, can only remind us of certain chemical, not natural, properties which they possess.

Vital air is essential to respiration, but these phenomena will be treated of afterwards with more propriety, under Carbon. Most other gaseous bodies, when breathed, speedily occasion disorganization, even though vital air enter the lungs at the same time. But nothing can supply the want of vital air. Without it suffocation sconer or later is induced. Neither can plants exist in regions from which it is excluded. It is the cup in which light is handed to sustain the functions of life, and from the simplest plants to the pulsation of our heart, all is dependent on the presence of vital air. As already mentioned, it constitutes rather more than one-fifth of the atmosphere. It is absorbed by water in very considerable quantities, and is always found wherever there is a medium suitable for the life of an organized body.

Deutoride of Hydrogen.-By a peculiar process, oxygen and