dized; and will be found, when weighed, to be considerably heavier than before. When completely oxydized in this mode, 100 parts of iron wire gain an addition of about 30.

V. Every substance, capable of union with oxygen, affords, by combustion, either an oxide, an acid, or an alkali.-When a body, by being burnt in oxygen gas, affords a compound, which has none of those qualities that characterize acids or alkalies, we denominate this product an oxide. If we collect, for example, the iron wire, which was burned in the last experiment, we shall find that it has lost all its metallic qualities, and has become a brittle, dark-coloured substance totally destitute of lustre and of taste, and termed an oxide of iron. But if, instead of iron wire, we had burned a quantity of sulphur in oxygen gas, over water, the result would have been that the water, which confined the gas, would have become acid or sour. Potassium, on the contrary (one of the new metals discovered by Sir H. Davy), would have yielded an alkali under the same circumstances. Hence the extensive class of combustible bodies may be subdivided into three orders; 1st, those which afford oxides by combination with oxygen; 2dly, those which yield acids; and 3dly, those which give alkalies. In many instances, however, a body is capable of passing through the intermediate state of an oxide, before it is converted either into an acid or an alkali.

VI. Oxygen gas supports, eminently, animal life.-It will be found that a mouse, bird, or other small animal, will live four or five times longer in a vessel of oxygen gas, than in one of atmospherical air of the same dimensions.

VII. This effect seems connected with the absorption of oxygen by the blood.-Pass up a little dark-coloured blood into a jar partly filled with oxygen gas, and standing over mercury. The gas will be in part absorbed, and the colour of the blood will be changed to a bright and florid red. This change to red may be shown, by putting a little blood into a common vial filled with oxygen gas, and shaking

it in contact with the

gas.

SECTION III.

Chlorine Gas.

I. THIS gas may be found by either of the following processes: Process 1. Into a stopper retort introduce eight ounces of liquid muriatic acid, and four ounces of finely powdered manganse, and ap ply the heat of a lamp. A gas will be produced, which may be received, in the usual manner, over water of the temperature of 80° or 90° Fahrenheit. From the foregoing materials about 160 cubical inches of gas may be obtained.

Process 2. Grind together in a mortar eight ounces of muriate of soda (common salt) with three ounces of powdered manganese ; put

them into a stoppered retort, and pour on them four ounces of sulphuric acid, which have been diluted previously with four ounces of water, and suffered to cool after dilution. Or the proportions recommended by Thenard may be employed, viz. 1750 muriate of soda, 450 oxide of manganese, water and sulphuric acid each 800. On applying a gentle heat gas will be produced, as in Process 1. But as the gas is absorbed by contact with cold water, though not rapidly, it should be received, when it is intended to be kept, in bottles filled with, and inverted in, water of the temperature of 80° or 90° Fahr. and provided with accurately ground stoppers. The stoppers must be introduced under water, while the bottle remains quite full of the gas, and inverted, and no water must be left in the bottle, along with the gas.

II. Chlorine gas has the following properties:

(a) It has a yellowish green colour: and this property has suggest ed the name chlorine*.

(b) It has a pungent and suffocating smell. In experiments on this gas, great care should be taken that it does not escape, in any considerable quantity, into the apartment; for its action on the lungs is extremely oppressive and injurious.

(e) It is heavier than common air (taking the statement of Gay Lussac) in the proportion of 2470 to 1000 by experiment, or 24216 by calculation; and 100 cubic inches should, therefore, weigh 75.33 grains. Sir H. Davy finds them to weigh between 76 and 77 grains, at a mean temperature and pressure, which would make its specific gravity 2.5082.

(d) By a temperature of +40° Fahr. it is reduced into a liquid form, and is condensed on the sides of the vessel. But if the gas be previously dried by exposure to muriate of lime, it bears a cold of 40° below 0 without condensation*.

When a receiver, filled with this gas, not artificially dried, is surrounded by snow, or pounded ice, the gas forms on its inner surface of solid concretion, of a yellowish colour, resembling, in its ra mifications, the ice which is deposited on the surface of windows during a frosty night. By a moderate increase of heat, such as to 50° Fahrenheit, this crust melts into a yellowish, oily liquid, which, on a farther elevation of temperature, passes to the state of a gas. (e) Chlorine gas, in its ordinary state, destroys all vegetable coIours. This may be shown by passing, into the gas confined by water, a piece of paper stained with litmus, the colour of which will immediately disappear. Hence the application of this gas to the purpose of bleaching, its power of effecting which may be shown by confining, in the gas, a pattern of unbleached calico, which gas, has been previously boiled in a weak solution of caustic potash, and then washed in water, but not dried. Chlorine gas, however, which has been carefully dried by solid muriate of lime, and into which per

fectly dry litmus paper is introduced, produces no change of colour in the litmus, a sufficient proof that its bleaching power depends on the presence and decomposition of water.

(f) This gas is absorbed by water; slowly, if allowed to stand over it quiescent, but rapidly when agitated.

1. The best method of effecting the impregnation of water with this gas, is by means of a Woulfe's apparatus, the bottles of which should be surrounded by ice-cold water. The quantity of the gas, which water is capable of absorbing, appears, from the concurrent testimony of Davy and Dalton, to be twice its bulk. The former has lately remarked that water, apparently saturated with chlorine by agitation with it in a narrow vessel, takes up more of the gas when exposed to it with a broad surface.

2. The watery solution, if perfectly free from common muriatic acid, has not the usual taste of an acid, but an astringent one. Its purity from muriatic acid may be ascertained by a solution of nitrate of mercury, which is not precipitated by pure chlorine.

3. The watery solution has the colour and peculiar smell of the gas, and has a similar property of discharging vegetable colours. Hence it may be employed in bleaching.

4. When the watery solution of chlorine is exposed to a temperature only a little above that of freezing water, the gas, which is combined with it, separates in the form of a liquid, heavier than

water.

5. Chlorine is not altered by the temperature of boiling water; for its solution may be raised in distillation, and again condensed without change.

6. When the solution of chlorine in water is exposed to the direct rays of the sun, oxygen gas is obtained, and the acid passes to the state of muriatic acid.

Chlorine is susceptible of combination with various other bodies, and the compounds possess, in many instances, remarkable properties. These will be made the subject of a distinct chapter in a subsequent part of the work.

SECTION IV.

Nitrogen or Azotic Gas.

AFTER separating, from any quantity of atmospherical air, all the oxygen which it contains, there remains a gas which was called by Lavoisier azotic gas, a name applied to it in consequence of its unfitness for supporting animal life; and derived from the Greek privative and a vita. This, however, as being merely a negative property, has since been deemed an improper foundation for its nomenclature: and the term NITROGEN gas has been substituted; because one of the most important properties of its base is, that by

a

union with oxygen it composes nitric acid. By this appellation therefore, I shall hereafter distinguish it.

I. Nitrogen gas may be procured, though not absolutely pure, yet sufficiently so for the purpose of exhibiting its general properties, in any of the following manners: 1. Mix equal weights of iron filings and sulphur into a paste with water, and place the mixture, in a proper vessel, over water, supported on a stand: then invert over it, a jar full of common air, and allow this to stand exposed to the mixture for a day or two. The air contained in the jar will dually diminish, as will appear from the ascent of the water within the jar, till at last only about four 5ths of its original bulk will remain. The vessel containing the iron and sulphur must next be removed, by withdrawing it through the water; and the remaining air may be made the subject of experiment.

gra

2. A quicker process, for procuring nitrogen gas, consists in filling a bottle, about one 4th, with the solution of nitrous gas in liquid sulphate of iron, or with liquid sulphuret of lime, and agitating it with the air which fills the rest of the bottle. During the agitation, the thumb must be firmly placed over the mouth of the bottle; and, when removed, the mouth of the bottle must be immersed in a cup full of the same solution, which will supply the place of the absorbed air. The agitation, and admission of fluid, must be renewed, alternately, as long as any absorption takes place.

3. Atmospheric air, also, in which phosphorus has burned out, affords, when time has been allowed for the condensation of the phosphoric acid, tolerably pure nitrogen gas.

4. Azotic gas may be procured from the lean part of flesh meat (beef for example), which may be put into a gas bottle, along with very dilute nitric acid. By a heat of about 100°, the gas is disengag ed, and may be collected over water. Its source has been satisfactorily traced to the animal substance, no part of it proceeding from the nitric acid.

II. Nitrogen gas has the following properties;

1. It is not absorbed by water.

2. It is a little lighter than atmospheric air, 100 cubic inches being found by Sir H. Davy to weigh 30-04 grains under a pressure of 30 inches, and at the temperature of 55° Fahrenheit. At 60° Fahrenheit 100 inches weigh, therefore, 29-73 grains. According to Biot and Arajo, its specific gravity is 0.96913.

3. It immediately extinguishes a lighted candle, and all other burning substances. Even phosphorus, in a state of active inflammation, is instantly extinguished when immersed in nitrogen gas. This is best shown by placing the burning phosphorus in a tin cup, raised by a stand over the surface of the water, and quickly inverting over it a jar filled with nitrogen gas.

4. It is fatal to animals that are confined in it

5. When mixed with pure oxygen gas, in the proportion of four parts to one of the latter, it composes a mixture resembling atmos pheric air in all its properties. Of this any one may be satisfied, by mixing four parts of azotic gas with one of oxygen gas, and im

mersing, in the mixture, a lighted taper. The taper will burn as in atmospherical air.

Composition of Nitrogen.

That nitrogen is not an element, but itself a compound, has been long suspected, and various attempts have been made to discover its ingredients. Some of the facts, which have been supposed to throw light on its nature, I shall reserve for the chapter of ammonia, because they will be better understood in connection with that subject.

Berzelius, from the combination of experiment with much theoretical reasoning, has deduced, that nitrogen is compounded of oxygen and an unknown base, in the following proportions*:

Base

... 44.32 ..

Oxygen 55.68

100

This base, it must be observed, however, is purely hypothetical; and, as it has never yet been exhibited in a separate state, we cannot at present know any thing of its properties. Berzelius has proposed for it the name of nitricum.

A series of experiments to prove the composition of nitrogen by synthesis, has been published in the 4th volume of Dr. Thomson's Annals, by Mr. Miers, of London. He attempted to deprive water of part of its oxygen by transmitting it, along with sulphurated hydrogen, through an ignited copper tube; by which process he obtained a mixture of oxygen and nitrogen gases, in proportions the same as those constituting atmospheric air. If no source of fallacy existed in the experiment, it would follow that nitrogen is composed of oxygen and hydrogen, with less oxygen than exist in water. But the experiments, though ingeniously devised, require the most careful repetition, before so important a conclusion can be established: and there is reason to suspect, from the nature of the products, that atmospheric air must, by some means, have found its way into the apparatus. It is remarkable, however, that the proportions of the elements of ammonia, deduced by Mr. Miers from his experiments, precisely agree with the hypothetical proportions assigned by Berzelius, viz. 55.6 oxygen and 44.4 hydrogen per cent. in weight.

The experiments of Sir H. Davyt, directed to the decomposition of nitrogen, on the presumption of its being an oxide, have not been attended with any better success. Potassium was ignited, by intense Voltaic electricity, in nitrogen gas; and the result was, that hydrogen appeared, and some nitrogen was found deficient. This, on first view, would lead to the suspicion, that nitrogen was decomposed. But, in subsequent experiments, in proportion as the potassium was more free from a coating of potash, which would introduce water, so, in proportion, was less hydrogen evolved, and less Phil. Tran. 1810.

*3 Thomson's Annals, 284.