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Properties of

which it entered, must be closed. The gas may now be drawn off at either of the stop-cocks, by a tube passing into the water-trough, or it may be propelled through a blow-pipe, or otherwise employed.

204. *Oxygen gas is insipid, colourless, and inodorous; its specific ⚫xygen gas. gravity is 16 hydrogen being assumed = 1. 100 cubical inches at mean

Supports respiration.

Stahl's idea of combustion.

Insufficient.

temperature and pressure weigh 33.88 grains.

205. It is a powerful supporter of respiration and combustion. A small animal, confined in oxygen gas, lives thrice as long as when confined in the same bulk of common air. A lighted taper, or a burning piece of sulphur, or phosphorus, introduced into this gas, is very rapidly consumed, with intense ignition.

206. The phænomena of combustion were referred by Stahl and his associates, to a peculiar principle which they called phlogiston; it was supposed to exist in all combustibles, and combustion was said to depend upon its separation; but this explanation was absurdly at variance with the well-known fact, that bodies during combustion increase in weight.

After the discovery of oxygen gas, it was adopted by Lavoisier as the Theory of La universal supporter of combustion. The basis of the gas was supposed to unite to the combustible, and the heat and light which it before contained in the gaseous state, were said to be evolved in the form of flame. But in this case, several requisites are not fulfilled; the light depends upon the combustible, and not upon the quantity of oxygen consumed; and there are very numerous instances of combustion in which oxygen, instead of being solidified, becomes gaseous during the operation; and, lastly, in others, no oxygen whatever is present. Combustion, therefore, cannot be regarded as dependent upon any peculiar principle or form of matter, but must be considerthe electrical ed as a general result of intense chemical action. It may be connecenergies of bo-ted with the electrical energies of bodies; for all bodies which power

Combustion may be connected with

fully act upon each other, are in the opposite electrical states of positive and negative; and the evolution of heat and light may depend upon the annihilation of these opposite states, which happens whenever they combine.

SECTION II. Of Chlorine.

207. To obtain this gas, a mixture of black oxide of manganese and muriatic acid may be heated over a lamp in a glass retort. It is

* As the specific gravities and atoms of the simple gases seem to be equimultiples of each other and as Thomson for very fair reasons has assumed the atom of oxygen as unity as well as its specific gravity in his late excellent paper, (ann. Philos; October, 1820), we will follow him in order also to point out this interesting connexion. The specific gravity of oxygen will therefore be supposed = 1.0 it has also been established, that, the atoms of all bodies, as far as examination has gone, are individually equamultiplies of the atom of hydrogen for the purpose therefore of commencing at a proper place, to exemplify this law, we shall here state the atom of hydrogen = 0.125 (that of oxygen being = 1), and refer to sect. 235 for the cal

culation.

:

1

2

soon copiously evolved, and may be conveniently collected over warm Method of obwater; it is absorbed by cold water, and cannot therefore be long re-taining chlotined over that fluid.

It may also be procured from a mixture of 8 parts of common salt, 3 of black oxide of manganese, 4 of water, and 5 of sulphuric acid.

203. Chlorine was discovered by Scheele in 1774; it was called Time of dis by him dephlogisticated muriatic acid. The term oxymuriatic acid my syn was afterwards applied to it by the French chemists.

noms.

209. Chlorine is a permanently elastic gaseous fluid; it has a pun- Characteris. gent and disagreeable smell, and is highly injurious when respired, ticar even largely diluted with atmospheric air. Its colour is greenish yel

low.

210. When dry, it suffers no change by exposure to the most intense cold, but in its ordinary state it contains aqueous vapour, which, at a temperature of 32°, is deposited in the form of a white crystalline compound, which effervesces, and is again taken up by the gas, upon the application of heat.

211. Chlorine is not altered by exposure to very high temperatures. Unaltered in By means of the following apparatus, Sir H. Davy exposed it to the high temperacontinued action of charcoal intensely ignited by Voltaic electricity, tures, without the smallest change in its properties.

A glass globe of about four inches' diameter, has at its upper part a sliding wire passing air-tight through a groundcollar, to the lower end of which is attached a piece of well-burned charcoal: at the bottom is a stop-cock supporting a brass pincers, in which is another pointed piece of charcoal; the globe is exhausted upon the air-pump, filled with chlorine, and the stop-cock and sliding wire attached to the extremities of the Voltaic apparatus; the charcoal points are then brought into contact by pushing down the upper wire, and they are thus retained as long as necessary in intense ignition.

*212. The specific gravity of chlorine, compared with hydrogen, is Specific gravias 36 to 1; 100 cubic inches weigh 76.25 grains.

ty.

ter, its use in

213. At the temperature of 60o, water dissolves two volumes of chlorine. The solution is of a pale yellow colour, has an astringent Solution in wanauseous taste, and destroys vegetable colours: hence its use in bleach-bleaching. ing; though the gas itself, when perfectly free from moisture, has

scarcely any action upon them,

214. When a burning taper is immersed in a jar of chlorine, the brilliancy of the flame is much impaired, it becomes red, throws off much charcoal, and is soon extinguished.

Many bodies such as phosphorus and several of the metals, are Union with spontaneously ignited by chlorine, and burn in it with much brilliancy.combustibles. In these cases binary compounds result, some of which, like those of

Sp gr. of chlorine 2.25 or just ths of 1 (the standard oxygen.)

[graphic]

i

219. Oxide of chlorine has an odour somewhat resembling that of Properties of chlorine, but much less irritating and disagreeable. Its taste is as-oxide of chlotringent, and not at all acid. It dissolves in water, forming a lemon-rine. yellow solution.

220. When oxide of chlorine is gently heated, it is decomposed when heated with explosion and expansion: two volumes are enlarged into three, is decomposed of which two consist of oxygen, and one of chlorine; it is therefore with explosion composed (of 36 parts by weight of chlorine, combined with 32 of composition. oxygen)*.

and expansion

221. Chloric acid. In the substance which has been thus called by Composition of its discoverer M. Gay-Lussac (Annales de Chimie, tom xci. p. 108,) chlorisacid. thet (relative proportions of chlorine to oxygen are to each other as 36. to 40.) But it is a compound which cannot exist, independent of water or some base, and, therefore, may be compared to the sulphuric and some other acids, afterwards to be described.

Preparation.

Chloric acid may be prepared by passing a current of chlorine through a mixture of oxide of silver and water. Chloride of silver is produced, which is insoluble, and may be separated by filtration. The excess of chlorine, which the filtered liquor contains, is separable by heat, and the chloric acid dissolved in water remains. It is a sour, colourless liquid, producing peculiar compounds, afterwards to be de- Properties. scribed. It forms no precipitate in any metallic solution. The compounds may be called chlorates. The most remarkable of them have been long known under the name of Oxymuriates.

222. Perchloric or oxychloric acid, is procured by distilling oxychlo- preparation rate of potassa (547) with its own weight of sulphuric acid. It con- and composisists of (36. chlorine + 56. oxygen.) It does not exist independent tion of perchi of water, or a base, and has been but imperfectly examined.

The proper terms for the above acids of chlorine would be Chlorous and Chloric acids, the former producing Chlorites and the latter Chlo

rates.

SECTION III. Of Iodine.

223. IODINE is procured by the following process: Lixiviate pow-process for obdered kelp with cold water. Evaporate the lixivium till a pellicle taining lodine. forms, and set aside to crystallize. Evaporate the mother liquor to dryness, and pour upon the mass half its weight of sulphuric acid. Apply a gentle heat to this mixture in the flask a of the alembic shown in the annexed figure, of which b is the head or capital, having a tube

• The gas, originally called Euchlorine by Sir H. Davy, appears to be a mixture of chlorine with the compound above described, and not a definite compound of two volumes of chlorine and one volume of oxygen. Should it, however, upon more accurate inquiry, prove a definite combination, it might be termed chlorous oxide, and the above compound would then be chloric oxide.

+ We have before remarked that the sp. gr. of chlorine (oxygen being 1) is = 2.25, if we also take the atom of oxygen = 1, then to find the atom of chlorine we have only to double the specific gravity, viz. 2.25 × 2 = 4.5, the same as deduced above, from the proportional Weights of constituents. Moreover the atom of hydrogen being already stated, = 0.125 tha atum of chlorine is evidently 36 times as great or = 4.5, 1. e. the atoms of these 2 gases are as their specific gravity. (Sec. 212.)

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ne form of opaque crystals, having a mewashed out of the head of the alembic ....er. and quickly dried upon bibulous paper. ocained from soap-makers' black ash by a evaporating the mother liquor to dryness, metimes greater when it is merely concen

sulphuric acid, boiled, and filtered: the ts weight of powdered black oxide of mandembic, or flask with a tube attached to its imes as before.

Vau

sered in 1812, by M. Courtois, of Paris. *wase, tom. xc.,) Gay-Lussac (ib. xc.,) and Davy ave fully investigated its properties. black colour; its lustre is metallic. It is a ty. It is soft and friable. *Its specific gravity yellow stain upon the skin. Its smell resemmerine; its taste is acrid. It is extremely volature between 60° and 80°, produces a violet

it rises more rapidly. At 220° it fuses, and et-coloured fumes, which condense in brilliant

carons.

Like chlorine and oxygen, it is electroe attracted by the positive surface of the Voltaic able colours yellow. It is very sparingly solu1d not holding more than 베이이이 its weight in soluDe solution is yellow. It is much more soluble ara ether.

... with oxygen and with chlorine, and gives rise which have been called Iodic, or Oxiodic, and

Trans. 1815.) This compound of oxygen ained directly, for those bodies exert no muIcared by acting upon oxide of chlorine by iodine.

have vapour is to that of Hydrogen, as 125: 1 and this x by the the atom of iodine thus 125 X 0, 125 = 15.625 atom Iodine.

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