himself to the dexterous management of collecting and transferring common air.

EXPERIMENT I.

Methods of transmitting air from one vessel to another.

If we are desirous of transferring air from one vessel to another, it is necessary that the vessel destined to receive it be full of water, or some fluid heavier than air. For that purpose, take a wide mouthed bell-glass or receiver, plunge it under the water in the trough in order to fill it, then raise it with the mouth downwards, and place it on the shelf of the trough, so as to cover one or more of the holes in it.

It will now be full of water, and continue so as long as the mouth remains below the surface of the fluid in the cistern; for in this case the water is sustained in the vessel by the pressure of the atmosphere, in the same manner as the mercury is sustained in the barometer. It may without difficulty be imagined, that if common air (or any other fluid resembling common air in lightness and elasticity) be suffered to enter the inverted vessel filled with water, it will rise to the upper part on account of its levity, and the surface of the water will subside. To exemplify this, take a glass or any other vessel, in that state which is usually called empty, and plunge it into the water with its mouth downwards, scarce any of it will enter the glass, because its entrance is opposed by the elasticity of the included air; but if the vessel be turned with its mouth upwards, it immediately fills, and the air rises in bubbles to the surface. If this operation be performed under one of the jars or receivers which are filled with water, and placed upon the perforated shelf, the air will ascend in bubbles as before; but, instead of escaping, it will be caught in the upper part of the jar, and expel part of the water it contains.

In this manner we see that air may be emptied out. of one vessel into another by a kind of inverted pouring; by which means it is made to ascend from the lower to the upper vessel. When the receiving vessel has a narrow neck, the air may be poured in a similar manner through an inverted funnel inserted in its mouth.

If the air is to be transferred from a vessel that is stopped like a bottle, the bottle must be unstopped with its orifice downwards in the water, and then inclined in such a manner that its neck may come under the perforated excavation of the shelf. The gas will escape from the bottle; and, passing into the vessel destined to receive it, will ascend in it in the form of bubbles.

In whatever manner this operation is performed, the necessity of the excavation in the lower part of the shelf may be readily conceived. It is, as mentioned before, destined to collect the gas which escapes from the vessel, and direct it in its passage towards the vessel adapted to receive it. Without this excavation, the gas, instead of proceeding to the place of its destination, would be dispersed and lost.

The vessels or receivers for collecting the disengaged gases should be glass cylinders, jars, or bell-glasses of various sizes; some of them should be open at both ends, others should be fitted with necks at the top, ground perfectly level, in order that they may be stopped by ground flat pieces of metal, glass, slate, &c. others should be furnished with ground stoppers; some should be graduated into cubic inches, and subdivided into decimal or other equi-distant parts. Besides these, common glass bottles, tumblers, &c. may be used.

CLASSIFICATION OF GASES.

All the elastic aeriform fluids with which we are hitherto acquainted are generally divided by systematic writers into two classes; namely, those that are respirable and capable of maintaining combustion, and those that are not respirable and incapable of maintaining combustion. This division indeed has its advantage; but the term respirable, in its physicological application, has been very differently employed by different writers. Sometimes by the respirability of a gas has been meant its power of supporting life, when repeatedly applied to the blood in the lungs. At other times all gases have been considered respirable which were capable of introduction into the lungs by voluntary efforts, without any relation to their vitality.

In the last case the word respirable seems to us most properly employed, and in this sense it will be used hereafter.

Non-respirable gases are those which, when applied to the external organs of respiration, stimulate the muscles of the epiglottis in such a manner, as to keep it perfectly close on the glottis ; thus preventing the smallest particle of gas from entering into the bronchia, in spite of voluntary exertions.

Of respirable gases, or those which are capable of being taken into the lungs by voluntary efforts, according to their conditions, only one has the power of uniformly supporting life, namely, atmospheric air: other gases, when respired, sooner or later impair the health of the human constitution, or perhaps occasion death, but in different modes.

Some gases effect no positive change in the blood; animals immersed in it die of a disease produced by the pri vation of atmospheric air, analagous to that occasioned by their submersion in water.

Others again produce some positive change in the blood, as appears from the experiments of Dr. Beddoes and Professor Davy. They seem to render it incapable of supplying the nervous and muscular fibres with principles essential to sensibility and irritability. These gases, therefore destroy animal life on a different principle.

It is obvious, therefore, that the above classification does not hold good in all respects, but is capable of misleading the student. We shall not divide the gases we are going to treat of into different classes, for we do not see the advantage which can arise from any division; we shall therefore examine first those which are simple, the bases of which cannot be exhibited in an insulated state, namely, oxygen, nitrogen, and hydrogen gas. We shall then consider the combination of these gases with each other, in order to understand some of the most important phenomena in which they are concerned, together with the rest of those gases, of which the bases may be exhibited experimentally.

OXYGEN GAS.

PART XV.

SECT. I.

PROPERTIES OF OXYGEN GAS.*

OXYGEN gas is an elastic invisible fluid, like common air, capable of indefinite expansion and compression. It has neither taste nor odour, nor does it show any traces of an acid. Its specific gravity, as determined by Kirwan, is 0.00135, that of water being 1.0000; it is therefore 740 times lighter than the same bulk of water. Its weight is to atmospheric air as 1103 to 1000. 116 cubic inches of oxygen gas weigh 39.38 grains. It is not absorbed by water, but entirely absorbable by combustible bodies, which at the same time disengage its caloric and light, producing in consequence a strong heat and flame. It rekindles almost extinct combustible bodies; it is indispensable to respiration, and is the cause of animal heat; it hastens germination; it combines with every combustible body, with all the metals, and with the greater number of vegetable and animal substances; it is considered as the cause of acidity, and from this last property is derived the name oxygen, a word denoting the origin of acidity.

The act of its combining with bodies is called oxydation (oxydizement) or oxygenation (oxygenizement) and the bodies with which it is combined are called oxyds.

Oxygen gas is the chief basis of the pneumatic doctrine of chemistry.

*From ous acid, and you, I am born.

METHODS OF OBTAINING OXYGEN GAS.

(See Appendix No. 15.)

We are at present acquainted with a great number of bodies from which we may, by art, produce oxygen gas. It is most amply obtained from the oxyds of manganese or mercury, from nitrate of potash, from the green leaves of vegetables, and from oxygenized muriate of potash, or soda. Besides these, there are a great many other substances from which oxygen gas may be procured.

EXPERIMENT I.

To obtain oxygen gas from oxygenized muriate of potash.

In order to procure oxygen gas in a state of great purity, pure oxygenized muriate of potash must be made use of. With this view, put some of the salt into a small earthen or glass retort, the neck of which is placed under the shelf of the pneumatic trough filled with water, and heat the retort by means of a lamp. The salt begins to melt, and oxygen gas will be obtained in abundance and of great purity, which may be collected and preserved

over water.

RATIONALE...Oxygenized muriate of potash consists of oxygenized muriatic acid and potash : at an elevated temperature a decomposition of the oxygenized muriatic acid takes place its oxygen unites to the caloric, and forms oxygen gas. The oxygenized acid becomes therefore converted into simple muriatic acid, which remains in the retort united to the potash, in the form of muriate of potash.

EXPERIMENT II.

To obtain oxygen gas from green leaves of vegetables.

Oxygen gas may likewise be obtained from the green leaves of vegetables.

For this purpose fill a bell glass with water, introduce fresh gathered green leaves into it, and place the bell or receiver inverted in a vessel containing the same fluid;