페이지 이미지
PDF
ePub

must at own be admitted that the separate existence of this base is a gratuitous Supposition On the part of Chemists, and has never yet been proved. Oxygen gas, however, may be obtained in great abundance, and it is this which we shall now describe. Its name is derived from two Greek words, Signifying producer of acids; but modern discoveries make it doubtful whether this is a correct application. It is, however^ now too late to alter it, unless a change in nomenclature is a less evil than having a word which, to the great mass of persons, does hot express the misapplied attribute.

Oxygen gas, the substance now to be described, is, both from the" nature of its properties and its wide diffusion through all the different parts of matter, one of the most Important bodies with which Chemistry has ever made man acquainted. Although no being can breathe without its presence, and no plant can live, and although it is the principal agent in all the

fihehomena of combustion, its exStence was only discovered first by Dr. Priestley, on August 1st, 1774, and was obtained by exposing red oxide of mercury to a burning lens. In consequence of a theory which then existed, but whidh is now exploded, he called ft dephlogisticated air. In 1774, Mr. Scheele, a very celebrated Swedish Chemist, without being at all acquainted with what Dr. Priestley had done, also discovered oxygen gas, and gave it the name of empyreal air. In the same year, Mr. Lavoisier, a French Chemist, equal in reputation either to Scheele or Priestley, succeeded, by his experiments, in expelling this gas from the red oxide of mercury, which first led him to suppose that metals absorbed a portion of atmospheric air when they were calcined, which may be considered as one of the facts that most conduced to establish the present and overthrow the phlogistic theory of Chemistry. Though the discovery of oxygen was of the highest importance, a'nd may

well be looked on as one of those events which, like the invention of the printing-press or the discovery of fluxions, has amazingly contributed to improve our knowledge of the particular science to which it relates, yet, from it having been made by two persons in countries remote from each other, though at no great distance of time, it would appear that it was, if we may so speak, a necessary discovery, and grew out of numerous other discoveries, which were then making in every place where Chemistry was studied- If neither Dr. Priestley nor Mr. Scheele had made us acquainted with it, some other person would. We do not say this to depreciate in any respect the great merit of these two distinguished Chemists: both of them, and more particularly our own countryman, whose researches were not con-v fined to Chemistry, have illustrated their names by several great and useful discoveries; but it appears to us, while we are humbly endeavouring to promote a knowledge of one branch of the external world, we may also sometimes take an opportunity of promulgating a truth of some importance, though not exactly scientific. This great discovery, though it very properly fell to the lot of two men who had long engaged themselves with chemical researches, Was not so much the result of their individual exertions, as of the general progress then making in Ghemistry in the whole of Europe. It is one more proof of the fact,' that every great and useful discovery is the result, not of particular circumstances or of chance, as it is sometimes expressed, but of general laws; and we dwell on it with pleasure, as the surest guarantee men can possess that the progress of society does not depend on accident, and is as certain as the laws of nature are permanent. We have individually, too, a pleasure in reflecting on this fact, and pointing it o-jt to the notice of our readers, because we infer from it, that though ungifted ourselves with any power to add to the stock of knowledge, we may,

by more extensively diffusing what is known, awaken the slumbering genius of many Newtons, and be the cause of other men making discoveries ; at least we shall secure tor those who improve science a larger share of reputation, and a juster appreciation of their merit. Oxygen gas, though diffused throughout nature, is then always combined with something else, and is never found or obtained pure but by some chemical means. We are not only indebted to Chemistry for a knowledge of its existence, but in its pure state it must be considered as a product of the laboratory. In our first Number, we described two separate methods of obtaining it; the following is another:—Take an iron bottle, capable of holding more than an English pint, of the shape represented in the figure.

[graphic][graphic][ocr errors]

To the mouth of this bottle a bent iron tube is to be fitted by grinding; and for this purpose a gun-barrel, with its buttend cut off, answers very well. Into the bottle put, in a state of powder, black oxide of manganese, a substance much in use with bleachers and other manufacturers; fix the iron tube into the mouth of the bottle, and make the joining air-tight by the luting recommended in last Number. Put the bottle into a common fire, and surround it with burning coals. The heat of the Cre first expels the atmospheric air contained in the tube, which soon ceases, however, to pass off. When the bottle has become obscurely red, air again issues from the end of the tube, and becomes more abundant as the

heat increases. The mouth of the tube is now to be placed in the pneumatic apparatus, exactly under the opening of the glass jar D. (in the plate of Number II.) The air gradually ascends to the top of the glass and displaces the water. The glass should be removed before all the water is forced out, and the dish or saucer in which it is removed should contain a little water, in order to prevent the escape of the air. After one glass is removed, anothermay be placed over the tube till as much of the gas is collected as is required. The air contained in these glasses is oxygen gas.

The method now described was discovered and employed by Dr. Priestley; the second method, described in Number I., is the method which was used by Scheele. The first method, described in our first Number, is, however, better than either of the others for obtaining the gas in a state of purity. There are several pther methods of obtaining it, but these are the easiest, and most generally cmployed. From whatever source obtained, the properties of oxygen gas are always the same, and are as follows:—It is colourless and invisible, like common air; it is elastic, like it, and susceptible of being compressed by mechanical means, having a tendency to dilate itself as the pressure is removed. It is found to be somewhat heavier than common air. Taking the specific gravity of the latter as 1.000, the specific gravity of oxygen gas is 1.1111,or,accordingto some authorities, 1.1115.

If a lighted taper be placed in a jar filled with oxygen gas, it burns with a splendour which the eye hardly dare look on; and the heat which it gives out is much greater than when burnt in the atmosphere. After a short period, the candle is extinguished. The same effect takes place if a candle is immersed in ajar of common air, from which the access of every fresh supply is excluded; but the candle burns longer in oxygen gas than in common air. Oxygen gas exists in a great quantity in the atmosphere, aud as a caudle will not hum in the other gases with which it is there combined, it has been concluded that it is the oxygen alone of the atmosphere which supports the ilame, and that without its presence, combustion, or what is, in common language, called burning, could not go on. In fact, it has been supposed, that combustion is, in all cases, only a rapid union of the combustible substance with oxygen, the heat and light being emitted either by the combustible, by the oxygen, or by both. Although tin's theory has been carried further than our knowledge at present warrants, for we cannot now say, since potassium burns in sulphuretted hydrogen, neither of which bodies contain oxygen, as far as we know, that this substance is necessary to combustion, and that it Will not go on if oxygen be not present; yet it has been demonstrated, that in all ordinary cases of combustion, oxygen combines with the combustible substance, and all tires kept uprnby the action of atmospheric air depend for their activity and intensity on the quantity of oxygen it contains. Admitting, therefore, that some other substances may possess the same property when in our laboratories, yet they are only, as far as we know, sparingly diffused; and oxygen gas is the great agent inall the alterations, whether the produce of nature or art, which are effected by means of fire. One conspicuous property, therefore, of oxygen gas, is that of supporting and promoting combustion; and it has been demonstrated, with very few exceptions, that the phenomena of combustion and the emission ef heat and light are caused byiaiapid union of oxygen with the substance consumed.

Though oxygen plays such an important part in all the phenomena which go on in dead matter, or in the mi animated part of crea-tion, it is of not less importance in all the phenomena of life, both in the vegetable and animal kingdoms. It was proved long ago, by the great philosopher, Boyle, that ani

mals cannot live without air, and by Mayow that they cannot breathe the same air for any length of time without suffocation. Dr. Priestley and various other philosophers have proved that animals live much longer in oxygen gas than in common air. It is even the oxygen gas alone of the atmosphere which seems to be consumed in respiration; and numerous experiments show that a quantity of it proportionate to the size of the animal is always absorbed by breathing. An ordinary man consumes about 32 ounces of oxygen gas every 24 hours; and to give the reader some idea of the immense quantity of it in bulk which is required, It is only necessary to state, that IWcubic inches, at the comnron pressure, do' not weigh above-30 grains. To supply the immense quantify of this gas, which is thus necessary for the existence of animals all over the globe, it is constantly reproduced by a beautiful provision in nature, which we shall hereafter describe.

Although oxygen gas is so necessary to life, it has, however, been also distinctly ascertained, that pure oxygen gas by itself is not well adapted to animal existence. An animal confined in it breathes in a hurried and laborious manner, and at length dies, even though a sufficiency of oxygen' gas is present to sustain the life of another animal of the same species. Plants, also, it is stated, will not vegetate unless oxygen gas have access to'their leaves. The whole theory of respiration, and the whole of the important part whiclroxyge'n gas performs in thisfuncfion,wbich is necessary to all animal life,'is" not yet known. Enough striking facts have, however, been ascertained, to show that oxygen gas is the stimulating, an,d,' we had almost said, the Hfe-giving principle' of the atmosphere. Air in which it is contained in abundance, increases the circulation of the brood, and imparts to the hitman frame all the marks of a more intense vitality; "while, on the contrary, air in which it is deficient, which

is contaminated by the breath of numerous persons, or the action of large (ires, is found to be little stimulant, and the persons who breathe it become languid, dull, and weary,as if the springs of their life were drying up. So striking and important, indeed, is this property of oxygen gas, that it was formerly called vital air, and a very distinguished Chemist of the present day, in the ardour of youthful imagination, did not hesitate to promulgate, at least in his conversation, an opinion that this gas was the essence of all vitality; that the mind of man was strong and vigorous in proportion to the oxygen contained in his frame and inhaled by his breath; and that oxygen was synonymous with what some ancient philosophers called the soul of the world. Although such a theory exceeds the bounds of our knowledge, the importance, and even the necessity of oxygen gas to the continuance of healthy animal and vegetable existence cannot be denied; and its use in supporting life may be considered as one of its most distinguishing properties.

In our classification, we stated that it was one of those few bodies which are evolved at the positive electrical pole, and of all bodies it appears to have this property in the highest degree. It is a necessary consequence of the other simple substances being evolved at the opposite pole, to suppose that when a compound substance containing oxygen is evolved at the positive side, that this is entirely owing to the presence of oxygen gas, and that no compound in which it, or one of the other simple substances having the same property, does not predominate, is ever evolved at this pole.

Of course a substance so important is extensively diffused. It is found in great abundance in the atmosphere, in the animal, in the mineral, and in the vegetable kingdoms. Twenty-one parts out of the hundred, in bulk, of the atmosphere, are oxygen gas; almost all the remainder is azotic gas

or nitrogen. Of water, eighty-five parts out of the hundred, in weight, arc oxygen; the other fifteen parts are hydrogen. Nearly all the products of combustion contain oxygen; and in almost all acids it is one main ingredient. The philosophic observer, who delights in tracing general laws, and who is struck with admiration at finding that—

"That rery law which moulds a tear, And bida it trickle from its source; That law preserves the earth a sphere. And guides the planets in their course,"

will be equally pleased at discovering that oxygen gas is possessed of the same properties wherever the researches of man have reached. It is found at the top of the highest mountains, and has been brought down from the heights of the atmosphere by those aerial voyagers who, in search of knowledge, have ventured even to soar far beyond, the eagle's utmost flight; it is met with wherever the miner has sunk his shafts; and it springs, forming one element of water, from the lowest depths to which the instruments of man have penetrated.

ACETAT OF MORPHrA, Since our last we have seen one foreign Journal in which some further information is contained on the subject of this poison. We observe with pleasure, that while the Chemists of our own country are condensing the gases to make them mechanic powers in the hands of man, our continental neighbours are engaged in the discovery of subtle poisons. In the Institute, on Monday, Jan. 2G, M. Dublanc, jun., an apothecary of Paris, announced to this learned body, that he had found in the alcoholic tincture of nutgalls a very sensible test proper to detect the presence of morphia in liquids, whether that substance exists in them uncombined or combined with either acetic or sulphuric acid.

M. Vauquelin, on the same day, made a report on a memoir of M. Lassaigne, on this subject, from which it results, 1st, That it is possible, in many oases of poison, by the action of morphia, to detect evident traces of this substance. 2d, That it is always in the viscera, to which the poison has been carried, that remains of it must be sought. 3d, That the substances rejected by vomiting, a short time after taking morphia into the stomach, contain a considerable quantity of it. 4th, That it is not possible, as far as we know, to discover any traces of acetat of morphia in the blood of any animal poisoned by it.

M. Lassaigne proceeded in this way:—If the presence of acetat of morphia was suspected in any liquid, he evaporated it by a gentle heat; he then treated the residuum with alcohol, to separate the animal matter and dissolve the acetat of morphia, as well as the osmazome and any salts. The alcohol is then evaporated. The residuum is dissolved in water, to separate a greasy substance, and this solution is allowed to evaporate spontaneously. When it contains acetat of morphia, it crystallizes in diver- . gent prisms, of a yellow colour, which are known by their bitter taste, by ammonia decomposing them, by acetic acid being disengaged when concentrated sulphuric acid is added; and, finally, by an orange red colour, which they assume when treated with nitric acid. If the acetat is, however, in very small quantity, it remains mixed with the osmazome, and will not crystallize; and in this case nitric acid detects its existence, by the orange red colour. If the examination is to be made of a solid substance, it is boiled about ten minutes in the water, and the above method is then pursued with this decoction. If the substances in which the presence of acetat of morphia is expected are of an alkaline nature, it is necessary to add to the alcohol or to the water a small quantity of acetic acid, to restore the acetat of morphia, which may have been decomposed.

Following this method of proceeding, the author found the acetat of morphia, 1st, in substances vomited by animals to which the

acetat had been given; 2d, in the stomach of a cat, which died after taking five grains of the acetat, but he found none in the intestines, in the heart, or in the blood of the same' animal; 3d, in a liquid in the thorax of a dog, which died in ten minutes after the injection of fourteen grains of the acetat; 4th, in the small gut of a cat, which died in ten hours after eighteen grains of this substance had been injected into this intestine; 5th, in the duodenum of a dog, which died in four hours and a half after eighteen grains of acetat had been injected into the duodenum; but no acetat of morphia was found in the blood of a dog, which was bled twelve hours after thirty-six grains of this poison bad been injected into the crural vein.

CHEAP WINE AND BRANDY.

The following methods of making those cheap Wines and Brandies, which the unwary lover both of money and liquor is tempted to buy, from seeing large placards stuck up in every part of the town, is taken from a pamphlet lately published by a wine-merchant. In addition, however, we must observe, that many of the ingredients out of which the cheap articles are made, are not of Nature's Chemistry,—are not the produce of the vineyard, but of the laboratory: —

s.<t. Take 2-3ds Cape, cost 15s. per doz. 10 0 Take l-3d very strong young Sherry or Teneriffe, Madeira, Lisbon, &c. the cheapest kind of Sherry, yet best calculated to mix in this manner, on account of its overpowering body and strong new flavour, cost 32s. per dor 10 8

£1 0 8

Apparently cheap price 2 2 0

Cost 10 8

Profit, £1 1 4

What a bargain! says the Purchaser. Cent, per ceut, says the Vender.

« 이전계속 »