out numerous sparks, exhibiting a very beautiful Here the combustion produces a appearance. combination of the oxygen with the carbon of the charcoal, and the result is carbonic acid.

A small bit of phosphorus, put into a copper spoon, burns in this gas with a light intensely bright. It is necessary to inform the young practitioner, that this experiment must be made with great caution. The phosphorus must be cut under water, and the piece employed must not exceed half the size of a small pea. The glass jar, in which the combustion is made, is not unfrequently broken by the heat. The result of this combustion is the phosphoric acid, from the combination of the phosphorus with the oxygen.

But

In all these cases, if the products of the combustions be carefully weighed, it will be found to exceed that of the substances burned, and the oxygen will be diminished, which shows they have absorbed a quantity of the oxygen employed. this is still further proved, because the oxygen may be extracted from these newly-formed compounds, and the original bodies will be thus made to re-appear.

If the metal potassium, or sodium, be burned in oxygen, they form, by their union with it, the alkalis, potass and soda; so that oxygen is not only an acidifying, but an alkalising principle.

Oxygen appears to be connected with the cause of the red colour in blood, for if dark coloured blood be put into a phial of oxygen gas and shaken, the blood will assume a bright red colour.

NITROGEN.

Nitrogen gas is so called, because its base forms nitric acid by its union with oxygen. It was by Lavoisier named azotic gas, and its base azote, from a Greek word signifying without life, because it is entirely destructive to animal life.

This, also, though a very abundant principle, cannot be exhibited in a free or uncombined state.

In the state of gas, it forms a considerable part of our atmosphere; in the solid state it enters into the composition of animal and vegetable bodies, nitric acid, and ammonia. It is incapable of supporting combustion or animal life. It is not absorbed by water, and it has no acid properties.

It may be obtained by separating the oxygen from a portion of the atmospheric air; the residue will be nitrogen. This is done by exposing a certain quantity of atmospheric air to sulphuret of potass, which absorbs the oxygen, leaving the nitrogen free.

It may be also obtained by treating muscular flesh, (as lean veal) with nitrous acid in a retort; the flesh is decomposed, and the nitrogen set at liberty.

That it does not maintain combustion, and is fatal to animal life, may be proved by plunging a lighted taper into a vessel filled with this gas, the taper will be immediately extinguished. If a small animal, as a mouse, or a bird, be immersed in it, it immediately dies.

COMBINATIONS OF OXYGEN AND NITROGEN.

Nitrogen and oxygen unite together in four different proportions:

1. Nitrous oxide, in which the oxygen is but half the volume of the nitrogen.

2. Nitric oxide, in which the volumes of oxygen and nitrogen are equal.

3. Nitrous acid, in which the volume of oxygen is twice the volume of nitrogen.

4. Nitric acid, in which the oxygen is two and a half times the volume of nitrogen.

Nitrous oxide. This gaseous compound, called also the gaseous oxide of nitrogen, or the gaseous oxide of azote, was first discovered by Dr. Priestley; but it is to Sir Humphry Davy that we owe a thorough knowledge of its properties.

Nitrous oxide is a permanent gas. A candle burns in it with a brilliant flame and crackling noise; before its extinction, the white inner flame becomes surrounded with a blue one. Phosphorus introduced into it, in a state of inflammation, burns with increased splendour, as in oxygen gas.

Sulphur, introduced into it when burning with a feeble blue flame, is extinguished; but when in a state of vivid inflammation, it burns with a rosecoloured flame. Lighted charcoal burns in it more brilliantly than in atmospheric air.

Iron wire, with a small piece of wood affixed to it, and introduced inflamed into a vessel filled with this gas, burns rapidly, and throws out bright scintillating sparks.

Nitrous oxide is rapidly absorbed by water that has been boiled, and a quantity of gas equal to rather more than half the bulk of the water may be thus

COMBINATIONS OF OXYGEN AND NITROGEN. 41

made to disappear; the water acquires a sweetish taste, but its other properties do not differ perceptibly from common water. The whole gas may be expelled again by heat.

It does not change blue vegetable colours. It has a sweet taste, and a faint, but agreeable odour. This gas explodes with hydrogen, when electric sparks are made to pass through the mixture. Animals, when confined wholly in this gas, give no signs of uneasiness at first; but they soon become restless, and then die.

When it is mingled with atmospheric air, and then received into the lungs, it generates highly pleasurable sensations. The effects it produces on the animal system are very extraordinary; it excites the body to action, and rouses the faculties of the mind, inducing a state of great exhilaration, an irresistible propensity to laughter, a rapid flow of ideas, and unusual vigour and fitness for muscular exertions, in some respects resembling the sensations attendant on intoxication, without any languor or depression of spirits, or disagreeable feelings afterwards; but more generally followed by vigour and a disposition to exertion, which gradually subsides.

This gas is produced when substances having a strong affinity with oxygen are added to nitric acid, or to nitrous gas. It may, therefore, be obtained by various methods, in which nitrous gas or nitric acid is decomposed by bodies capable of attracting the greater part of their oxygen. The most commodious and expeditious, as well as cheapest mode of obtaining it, is by decomposing nitrate of ammonia by heat, in the following manner: put into a glass retort some pure nitrate, and apply to it an Argand's lamp; the salt will soon liquify, and

42 COMBINATION:S OF OXYGEN AND HYDROGEN.

when it begins to boil, gas will be evolved. Increase the heat gradually, till the body and neck of the retort become filled with a milky white vapour. In this state, the temperature of the fused nitrate is between 340° and 480°. After decomposition has proceeded for some minutes, so that the gas, when examined, quickly enlarges the flame of a taper, it may be collected over water. Care should be taken, during the whole process, never to suffer the temperature of the fused nitrate to rise above 500° of Fahrenheit; which may be easily judged of from the density of the vapours in the retort, and from the quick ebullition of the fused nitrate; for if the heat be increased beyond this point, the vapours in the retort acquire a reddish and more transparent appearance, and the fused nitrate begins to rise, and occupy twice the bulk it did before. The nitrous oxide, after its generation, should stand over water for several hours; it is then fit for respiration or other experiments.

The explanation of this process is as follows: Nitrate of ammonia consists of nitric acid and ammonia; nitric acid is composed of nitrous gas and oxygen; and ammonia consists of hydrogen and nitrogen. At a temperature of 480°, the attractions of hydrogen for the nitrogen in the ammonia, and that of nitrous gas for the oxygen of the nitric acid, are diminished; while, on the contrary, the attractions of the hydrogen of the ammonia for the oxygen of the nitric acid, and that of the remaining nitrogen of the ammonia for the nitrous gas of the nitric acid, are increased; hence all the former affinities are broken, and new ones produced; namely, the hydrogen of the ammonia attracts the oxygen of the nitric acid, the result of which is water. The nitrogen of the