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potass together in equal parts, after trituration in a porcelain mortar. This fluid has an acid, astringent taste, and the name iodous acid has been given to it; but the proportion of its elements has not been ascertained. Quarterly Journal of Science and Art, xvii. 381.

335. Chloriodic acid, or as it is called by Gay Lussac chlorure of iodine, is obtained by the direct action of chlorine upon iodine, iodine absorbing less than one-third of its weight of chlorine; the union produces crystals of a deep orange color. Gay Lussac states indeed that two compounds are the result of this combination, the one, as noticed, of a deep orange color, the other an orange red, the largest portion of chlorine being contained in the first.

336. Chloriodic acid precipitates the salts of iron and other metals.

337. Nature of Iodine (From Dr. Henry's Elements). Iodine, from all that we yet know respecting it, is to be considered as a simple or elementary body, having a very striking analogy with chlorine, which it resembles, firstly, in forming one acid by uniting with hydrogen, and a different acid with oxygen; secondly, in its effects on vegetable colors; thirdly, in its affording with the fixed alkalis, salts, which nearly approach in character to chlorates; and fourthly, in its electrical habits. Its discovery indeed lends strong support to that theory which considers chlorine as a simple body, and muriatic acid as a compound of chlorine and hydrogen. In the property of forming an acid, whether it be united with hydrogen or oxygen, iodine bears also an analogy to sulphur; and it is remarked by Gay Lussac of the combinations of chlorine, iodine, and sulphur, with the elements of water, that while the acids which they respectively form with oxygen have their elements strongly condensed, those formed with hydrogen have their elements very feebly united. Sulphur has the strongest affinity for oxygen, then iodine, and lastly chlorine. But for hydrogen, chlorine has a stronger attraction than iodine, and iodine than sulphur; whence it appears that the affinity of each of those bodies for oxygen is inversely proportionate to its affinity for hydrogen.

338. The source of iodine in nature has been investigated by M. Gaultier de Claubry. His first experiments were directed to the several varieties of fucus, the combustion of which furnishes the soda of sea-weeds. Before these vegetables are destroyed by combustion he ascertained that iodine exists in them, in the state of hydriodate of potassa; and that calcination only destroys the vegetable matter with which it is combined. As the bydriodate of potassa is a deliquescent salt, it remains in the mother liquor after separating the carbonate of soda, and most of the other salts, by crystallisation. In the course of these experiments M. De Claubry found that starch is one of the most delicate tests of the presence of iodine, and if added to any liquid containing it, with a few drops of sulphuric acid, iodine is indicated by a blue color of greater or less intensity. In this way he detected iodine in the decoction of several varieties of fucus; but he was unable to discover the slightest trace of it in sea-water. The fucus saccharinus yielded

it most abundantly; and, in order to obtain it by the cheapest and easiest process, he recommends that we should submit this fucus, dried and re duced to powder, to distillation with sulphuric acid.

339. In the Addenda to Dr. Henry's Elements, we meet with the following additional notification in reference to the source &c. of iodine: The only known sources of iodine were certain vegetables and some marine molluscæ, till Vauquelin discovered it a few months since in the specimen of a mineral, sent from Mexico, under the name of Virgin silver from Serpentine.' The best method of separating the iodine from this substance was found to be as follows: Five parts of the pulverised mineral were heated with two parts of caustic potassa, and a little water to facilitate the mixture; and kept some time in fusion. The mass was washed with water till the latter ceased to become alkaline; a portion of the liquor saturated with nitric acid has the property of rendering starch blue, when a few drops of solution of chlorine had been previously added. Of the portion insoluble by water, diluted nitric acid dissolved a part with effervescence; but there remained a yellowish substance resembling chloride of silver, which became orange colored by heat, and passed to a greenish yellow on cooling. This substance was iodine of silver.

340. The alkaline liquor afforded hydriodate of potassa, by saturating the alkali with sulphuric acid, evaporating to dryness, and adding alcohol, which took up the hydriodate only, leaving the sulphate of potassa. The whole iodine thus extracted from 100 grains of the ore, Vauquelin calculates at 18 grains; and on reviewing the composition of the ore, the other ingredients of which were sulphur, lead and silver, he considers it as most probable that all the iodine contained in the native mineral was united with the latter metal. It is probable that with this clue to more perfect analysis, iodine will be found in othe minerals, and especially in ores of silver, for which metal it has like chlorine a strong attraction. Ann. de Chym. et de Phys. xxix. 991.

341. FLUORINE. This is a principle which has not hitherto been obtained in a separate state; it seems to be united with hydrogen in the fluoric acid; this acid, like the muriatic, appears to be composed of hydrogen, and a peculiar base, which base in the instance before us, has been denominated fluorine by Sir H. Davy; and phtore from 40opios, destructive, by Ampére: it possesses a negative electric energy, which is proved by its being determined to the positive pole.

342. It exists in the fluor spar, a mineral found in great beauty and abundance in Derbyshire. This spar is stated to be composed of twenty calcium, and 17.1 fluorine. See FLUORIC ACID.

343. ELECTRO-POSITIVE BODIES.-The bodies which fall now to be considered have been usually classed as inflammable or combustible; to this appellation, Dr. Henry very properly states, that the same objection exists as to that of supporters of combustion. Against our author's own classification, it may, however, be objected that the title of electro-positive includes all substances with the exception of the few just noticed. Dr. Henry, indeed, anticipates this objection, and

proposes a subordinate division of elementary bodies, that is of those bodies which have not hitherto been resolved into a more simple

state.

344. i. Those which by combining with oxygen, chlorine, or hydrogen, are capable of being converted into acids, but which have no metallic properties.

345. ii. Those which either decidedly rank as metals, or are so nearly allied to metals in their general habitudes, as to render it improper to assign to them any other place in a chemical arrangement. In the class of metals will be found a few bodies which yield acids when united with oxygen; and one or two which are even acidified by combination with hydrogen.

346. One great advantage, as it appears to us, in adopting this arrangement, is, as above-intimated, that it preserves in the student's mind a constant recollection of the great principles of electro-chemical science, and of the immense benefit these new views have already conferred on chemistry, and still promise to confer.

347. In Mr. Brande's Manual, which cannot be too highly recommended to the student, the following substances are introduced for consideration in his division, under the title of Simple Acidifiable and Inflammable Substances; and he prefaces the notice of them by stating that the bodies belonging to this class are electro-positive, and consequently, when separated from their combinations with the substances described in the last chapter, (oxygen, chlorine, iodine), by Voltaic electricity; they are attracted by the negative surface. With very few exceptions they combine with the three supporters of combustion already described, and of these compounds one or more are acids. They are six in number. 1. Hydrogen. 2. Nitrogen. 3. Sulphur. 4. Phosphorus. 5. Carbon. 6. Boron. The plan that we are about to pursue will lead to the investigation of these bodies and principles, almost in the direct order, thus adopted by Mr. Brande. They are all acidifiable, but not all in strict propriety combustible or inflammable bodies.

348. HYDROGEN. See AIR, p. 381.-Hydrogen exists in a state of gas, or, in other words, it is combined with caloric, and probably with electricity and light, to such an extent as to occasion its gaseous constitution, and from this combination we cannot separate it any other other way than by causing it to combine with some other substance. This gas was first attentively examined by Mr. Cavendish; it was formerly termed inflammable air. It may be prepared by the action of dilute sulphuric acid upon iron filings or upon zinc. The gas will escape, and may be collected in the usual manner. Mr. Donovan has proposed, in order to purify the gas from admixture with sulphuretted hydrogen and carbonic, that we should first agitate common hydrogen with lime water during a few minutes; next with a little nitrous acid; afterwards with a solution of green sulphate of iron, and finally with water. Dr. Henry, in alluding to this proposal, says it appears to him that the carbonic acid, and sulphuretted hydrogen, may equally well be removed by the simple process of washing the crude gas, either with lime-water or with a solution of caustic potassa.

349. For the properties and peculiarities of hydrogen gas, we refer to the article AIR; but we may quote in this place an illustration which is given in Dr. Henry's work, of the fact that elastic fluids or gases penetrate each other, and become thoroughly mixed under all circumstances; in this, differing from common or inelastic fluids (liquids) which are capable of a remaining in contact with each other for a long time without admixture.

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320. Provide twa glass vials, each of the capacity of about an ounce measure, and also a tube open at both ends, ten inches long, and 1-20th inch bore. At each end the tube is to be passed through a perforated cork, adapted to the necks of the vials. Fill one of the bottles with hydrogen gas, and the other with oxygen gas; place the latter on a table with its mouth upwards; and into this insert the tube secured by its cork. Then holding the hydrogen bottle with its mouth downwards, fit it upon the cork at the top of the tube. The two bottles thus connected, are to be suffered to remain in this perpendicular position. After standing two or three hours, separate the vials and apply a lighted taper to their mouths, when it will almost certainly occasion an explosion in both. The hydrogen gas, though sixteen times lighter than the oxygen, must, therefore, have descended through the tube from the upper into the lower vial; and the oxygen gas, contrary to what might have been expected from its greater weight, must have asscended through the tube, and displaced the lighter hydrogen.'

351. Hydrogen and Oxygen. (Water.)-Mix two volumes of hydrogen gas with one volume of oxygen gas, and inflame the mixture by the electric spark in a proper apparatus; the gases will by this treatment disappear totally, and the inner surface of the vessel will be moistened with a fluid which will be found to be pure water, and equal in weight to the gases which have disappeared.

352. Again, expose pure water to the action of Voltaic electricity, and you resolve it into hydrogen, which will be disengaged at the negative pole, and oxygen will be disengaged at the positive pole; the hydrogen will be two volumes, the oxygen one, so that water is demonstrated both by synthesis and analysis to be formed of hydrogen and oxygen, in the proportion of two volumes of the former to one of the latter.

353. Under the word WATER, in the body of the work, we shall enter into a disquisition on its properties; it may be here generally stated, that in its ordinary and natural state, such as spring and river water, it always contains air, and that it is always so far combined with foreign substances as considerably to interfere with its abstract existence. The water immediately from rain is purer, but even this always contains some of the atmospherical elements, and also some traces of vegetable or animal matter. Even after water has been distilled, some impurities or particles of foreign matter remain in it, and to render it completely free from these impregnations, it requires to be slowly and carefully redistilled. More or less of water is ever contained in the air of the atmosphere, even in the dryest weather, and many bodies, from mere ex

are

posure to the atmosphere, will abstract a portion of it, or in other words of its moisture; such the deliquescent salts mentioned under the nead of crystallisation. Whether aqueous fluids exist in the atmosphere chemically combined, or merely mechanically mixed, has been made a question; or rather, it has been debated whether it is chemical solution or mere calorific influence which retains that portion of fluid in the air which is capable of being deposited by an alteration of circumstances; it is most consistent with the general analogy of material existence, perhaps, to suppose the latter to be the

case.

354. M. Thenard has shown that an additional quantity of oxygen may be made to unite with water, so as to constitute a very different proportion of hydrogen and oxygen in composition, than the proportion of water. This combination is effected by means of the peroxide of barium, a substance afterwards to be described. See Quarterly Journal of Science and Art, vol. viii. p. 114, 115.

355. Hydrogen with Chlorine, Muriatic Acid, or, more consistently with the new theory and nomenclature, Hydro-chloric Acid.-Mix equal quantities of hydrogen and chlorine, and expose them to the action of a lighted taper, or even to the direct action of the sun's rays, an explosion or detonation will take place; the same effect will be produced by Voltaic electricity, showing, says Mr. Brande, a curious analogy between electric and solar light; for ordinary artificial light does not accelerate the combination (see Brande's account in the Philosophical Transactions of 1820). The produce of the union of equal parts of chlorine, whether effected suddenly and with explosion, or silently, is muriatic, or more properly speaking, hydrochloric acid gas. 356. This acid is procurable by other methods; it may be obtained by pouring sulphuric acid on common salt, the sulphuric acid unites in this case with the base of the salt, and the muriatic acid is evolved in the form of gas.

357. Muriatic acid gas has a pungent smell, it is caustic in its action upon the skin, it extinguishes flame, it is heavier than common air. Its specific gravity is stated by Gay Lussac to be 1-278; 100 cubic inches, according to Mr. Brande, weigh 38.8 grains. It is very rapidly absorbed by water, and, when dissolved in that fluid, it forms the liquid muriatic acid, for the mode of preparing which, and for the theory of its formation, see HYDROCHLORIC ACID.

358. This acid in a liquid state manifests the following properties. It emits suffocating whitish fumes, it affords muriatic gas by being heated with heat. When diluted with water an elevation of temperature is occasioned; it combines freely with the alkalis and with most of the earths, both in their caustic, or rather pure, and their carbonated states. It is specifically heavier than water. When brought into contact with any substance containing oxygen in a state of loose combination, its hydrogen unites with this oxygen, forming water, while the chlorine becomes liberated in the state of gas. Indeed chlorine is procured in this way, but it is usual not to employ the already formed liquid acid

for the purpose, but to use the materials that have the power of furnishing the acid gas, as the chloride of sodium (common salt), oxide of manganese, and sulphuric acid.

359. On the theories which have prevailed respecting Chlorine and Muriatic Acid.-As these have an important bearing upon the legitimacy of the new electro-chemical doctrines, we shall take the liberty of extracting verbatim, the account of them, found in Dr. Henry's volumes. There are few subjects,' says Dr. Henry, 'respecting which the opinions of chemists have undergone such frequent changes as concerning the nature of chlorine and of muriatic acid. The views originally taken by Scheele, the illustrious discoverer of the former substance, was that the muriatic acid is compounded of a certain base, and an imaginary principle called phlogiston (see part 1st.); and that by the action of certain bodies it became dephlogisticated, or deprived of that supposed principle of inflammability. It was afterwards found, however, that all bodies which are capable of producing this change in muriatic acid contain oxygen, and that their portion of oxygen is diminished by the process. It appeared, therefore, to be an obvious conclusion, that what takes place in the action of metallic oxides on muriatic acid, is simply the transference of oxygen from the oxide to muriatic acid; and, conformably with this theory, the resulting gas received the name of oxygenated muriatic, or oxymuriatic acid. Sir H. Davy was led by his early experiments to modify in some degree this view of the theory of the process; and to consider the muriatic acid as a compound of a certain basis with water; and the oxymuriatic acid as a compound of the same basis with oxygen. This modification was rendered necessary by the fact, that when a metallic body is heated in muriatic gas, oxymuriatic acid is obtained, and water appears in a separate state. It was evident, therefore, that muriatic acid gas must either contain water ready formed, or the elements of water, or hydrogen capable of composing water with the oxygen of the oxide. But at a subsequent period, the same distinguished philosopher vas induced by the experiments of Gay Lussac and Thenard, as well as by his own researches, to form a different theory on the subject. Oxymuriatic acid he now considers as a simple or undecompounded substance; and muriatic acid as a compound of that simple substance with hydrogen. To convert the muriatic acid into chlorine we have only, according to this view, to abstract hydrogen from the muriatic acid, and this, it is believed, is all that is effected by the action of those oxides which are adapted to the purpose. Again, to convert chlorine into muriatic acid, we have only to combine it with hydrogen; and accordingly, the simple mixture of one measure of each of these gases, when exposed for a short time to the sun's rays, or exploded by an electric spark, affords two measures of muriatic acid gas.

360. The oxymuriatic acid, or chlorine, as Sir H. Davy proposes to call it, in order to avoid all connexion of its name with hypothetical views, is supposed also to unite at once with

the metals, without requiring, like the sulphuric, nitric, and other acids, that the metals should first be in the state of oxides. In proof of this theory it appears to be sufficiently established, that no oxygen can be obtained either alone, or in a state of combination with combustible bodies added for the purpose, from the compounds of chlorine and metals. The analyses, however, of the metallic muriates, as they were formerly considered, remain unimpeached by this change of theory. All that is necessary to transmute in ideas a muriate, into a compound of chlorine, is to deduct the oxygen from the metallic oxide; and adding to it the muriatic acid, to consider the same as chlorine. For example, muriate of soda, deprived of all water, consists,

On the old theory, of muriatic acid 46.7 28

Davy, in the 34th volume of Nicholson's Journal; to Sir H. Davy's paper, in the Philosophical Transactions for 1818, p. 169; to the 8th vol. of Transactions of the Royal Society of Edinburgh; the Annals of Philosophy, 12th vol. 379, and xiii. 26, 285; and to a paper by Mr. R. Phillips in the new series of that work, vol. 1st, p. 27, on the action of chlorides on water.' Henry.

363. Hydrogen and Iodine.-When iodine is presented to nascent hydrogen,a union is produced and a gaseous acid is the result, which is named hydriodic acid. This gas is best prepared in any quantity, by the action of moistened iodine, upon phosphorus. It is received over mercury, but, as it is soon decomposed by that metal, it should be transferred as soon as possible into an exhausted vessel.

364. This acid is colorless, and has an ex

Soda composed of {x 400 533 32 tremely sour taste; it smells like muriatic acid.

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361. According to this view, the atom of dry muriatic acid (hydrogen being unity, and oxygen 8), would be equivalent to 28; and this + 8 (1 atom of oxygen), would give 36 for the atom of oxymuriatic acid. The latter number, indeed, still represents the atom of chlorine as deduced from the fact, that it unites with an equal volume of hydrogen gas, and is 36 times specifically heavier than that inflammable gas. We may consider then, 60 parts of common salt as composed, according to the old view, of 28 parts dry muriatic acid, and 32 parts of soda, (24 sodium and 8 oxygen), or of 24 sodium +36 chlorine, according to the new theory.

362. It is remarkable, that there is hardly any fact connected with the chemical history of chlorine and muriatic acid, that does not admit of being almost as well explained upon the hypothesis that chlorine is compound, as upon that of its being a simple substance. On the whole, however, the weight of evidence is very much in favor of the new, or rather the revived opinion of its elementary nature, especially since the discovery of iodine; and I have little scruple, therefore, in adopting it, as affording the most simple and satisfactory explanation of phenomena, as well as the best ground-work for a conspicuous arrangement of the objects of chemistry. The reader who wishes to examine fully the evidence for both opinions, is referred to the controversy between Dr. Murray and J.

Its specific gravity, as compared with hydrogen, is given as 59.3 to 1; 100 cubic inches weighing 133.6 grains.

365. In a liquid form it is best procured by passing sulphuretted hydrogen through a mixture of iodine and water; sulphur becomes deposited, and, on heating and filtering the liquor, we obtain a pure solution of hydriodic acid.

366. This liquid acid is slowly decomposed by the action of atmospheric air, its hydrogen is attracted by the oxygen of the air, and a portion of iodine is thereby rendered free, which colors the liquor. It is likewise decomposed by concentrated sulphuric, by nitric acid, and by chlorine. Voltaic electricity rapidly decomposes the liquid acid, iodine appearing at the positive, and hydrogen at the negative pole. Although the acid gas so powerfully acts upon mercury, the liquid acid does not affect it. Those bodies called oxides, in which the oxygen is loosely combined, readily decompose the acid, and neutral salts are obtained, called hydriodates; a process of preparing the hydriodate of potass, is given in the new series of the Annals of Philosophy, vol. vii. p. 48. We mention this on account of the salt having lately been employed as an important article in medicine. See MEDICINE.

367. Hydrogen with Fluorine (Fluoric acid). This is introduced here under the presumption that hydrogen is its acidifying principle; there appears,' says Dr. Henry, every reason to believe, that hydrogen is the acidifying principle of fluoric acid, and that, in the same manner as hydrochloric acid is constituted of chlorine united with hydrogen, this acid also consists of a peculiar base, belonging, like chlorine, to the electro-negative class of bodies, and rendered acid by combination with hydrogen.' To this basis, though not yet exhibited in a separate state, the name of fluorine has been given, and the acid has been termed hydrofluóric.

368. This acid may be procured in a liquid state, by distilling the powdered fluor spar, with twice its weight of strong sulphuric acid. Mr. Knight, in the seventeenth volume of the Philosophical Magazine, has described and represented an ingenious apparatus for the purpose.

369. One peculiarity of the fluoric acid is, that it acts strongly on glass; hence it has been employed for etchings on glass. This peculiarity makes it of course necessary to preserve it in bottles, composed of materials which the acid has not power thus to corrode, those of silver or lead may be used.

370. Fluorine, it will be recollected, is at present rather a supposed than an actually demonstrated base. The fluates are still treated of by some chemists as compounds of fluoric acid with metallic oxides; but Sir H. Davy and M. Ampére, as we have already stated, consider them as compounds of metals, with a peculiar principle analogous to chlorides, which has been called fluorine or phtore. Fluor spar, for example, may be either a fluate of lime, or a fluoride of calcium. And in the same manner that we convert, in imagination, a muriate into a chloride, we may change a fluate into a fluoride. Thus fluor spar may be constituted either of

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Weight of the atom of anhydrous fluate of lime

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1 atom of fluorine, 10 + 8

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18

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hitherto without success, to discover the ingredients of which nitrogen is composed, supposing it to be a compound body. Sir H. Davy ignited, by means of intense electricity, potassium in nitrogen gas, and hydrogen appeared as the result, some nitrogen being at the same time found deficient. Hence it was supposed that the nitrogen had suffered some decomposition, but in further experiments it was ascertained that n proportion to the potassium being free from. a coating of potassa, which contains water, in that proportion, was less hydrogen found to appear, and less nitrogen was also observed to be wanting.

374. Nitrogen and Oxygen.-Besides the proportion of nitrogen with oxygen that forms at mospheric air, and for an account of which we refer to the article AIR, these bodies are known to unite in four other proportions, and constitute the compounds called,

i. Nitrous oxide of Davy, or the protoxide of nitrogen.

ii. Nitric oxide, or deutoxide of nitrogen. iii. Nitrous acid.

iv. Nitric acid.

375. Nitrous Oxide.-The salt called nitrate of ammonia will yield this gas, by being heated 38 in a retort to a temperature of between 420 and 430°. It may be collected over water. The theory of its formation is as follows: nitric acid is made up of oxygen and nitrous gas, as we shall shortly state; the component parts of ammonia are hydrogen and nitrogen. By an increase of temperature, the nitrous gas combines with an additional dose of nitrogen, and thus nitrous oxide is formed; the oxygen of the decomposed nitric acid unites with the hydrogen of the ammonia, and forms water.

1 atom of calcium Weight of the atom of fluoride of calcium 38 371. It should be added, that if the latter views be correct, fluates, like muriates, can only be capable of existing either in solution, or in a state of hydrous salts. The actual conversion of a fluoride into a fluate will then be attended with the decomposition of an atom of water; and 1 of hydrogen by weight will unite with 18 fluorine, making the real atomic weight of fluoric acid 19, while 8 of oxygen will unite with the atom of metallic base. The atomic weight of the fluate will, in that case, be 19+ that of the alkaline, or earthy base, or 9 (= to an atom of water) more than the number assigned to the anhydrous compound.' Henry.

372. NITROGEN, OR AZOTE (see the article AIR, p. 380, No. 56,-Nitrogens, or azote, (the latter word derived from the Greek à and Cwn,on account of the unfitness of the gas for supporting animal life), was first recognised as a distinct aeriform fluid in 1772. In addition to the modes of procuring it, as stated under AIR, we may give the following: fill a bottle about one-fourth with the solution of nitrous gas, in liquid sulphate of iron, or with liquid sulphate of lime, and agitate it with the air that 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, so long as any absorption takes place.

373. Various attempts have been made, but

376. Nitrous oxide gas has the following characteristics: it is heavier than common air, 100 cubic inches weighing, according to Brande, 46 125 grains; compared with hydrogen, its specific gravity is 20.5 to 1. Its taste is sweet, and its smell not disagreeable. It is easily absorbed by water. It supports combustion, and a taper immersed in it burns brilliantly, sometimes with a crackling noise. Red-hot charcoal burns in it with brilliancy, and consumes some of its oxygen. Many of the metals likewise decompose it at a high temperature. This gas detonates with hydrogen, and the best analysis of it is effected in this manner: one volume of nitrous oxide requires one volume of hydrogen. This mixture, fired by the electric spark, produces water, and one volume of nitrogen remains. Now, as one volume of hydrogen takes half a volume of oxygen to form water, nitrous oxide must consist of two volumes of nitrogen and one volume of oxygen; these three volumes being so condensed, in consequence of chemical union, as only to fill the space of two volumes. The specific gravity of nitrogen, compared with oxygen, is as 13 to 15. Nitrous oxide therefore consists of

Number for nitrous oxide

13 Nitrogen 7.5 Oxygen

20.5

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