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248. Hydrogen and Chlorine. When equal volumes of these gases Muriatic acid. are mixed and exposed to light, they combine, and produce a sour compound commonly called muriatic acid gas; or, in conformity to more modern nomenclature, hydrochloric acid gas. If the above mixture be exposed to the direct solar rays, a detonation ensues, as was first remarked by M. M. Gay-Lussac and Thenard. (Recherches Physico-Chymiques, ii. 129.) It also detonates when exposed to the light of the Voltaic discharge, showing a curious analogy between electric and solar light; for ordinary artificial light does not accelerate the combination. BRANDE, Phil. Trans. 1820.

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The best mode of showing the composition of muriatic acid, is to introduce into a small but strong glass vessel a mixture of the two gases, and to inflame them by the electric spark; no change of volume ensues, and muriatic gas results. The apparatus shown at page 334, may be used for this purpose.

muriatic or by

249. Muriatic acid may be decomposed by the action of several of the metals. Potassium, for instance, absorbs the chlorine, and the hydro-Analysis of gen is evolved; muriatic acid gas thus affords half its volume of hydro-dro-chlorine gen. As the specific gravity of hydrogen to chlorine is as one to 36.0, muriatic acid will consist of 1 hydrogen + 36.0 chlorine, and its representative number will be 37.0.

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250. Muriatic acid may be readily procured by acting upon common salt by sulphuric acid; the evolved gas must be received over mercury. It was first obtained pure by Dr. Priestley, but its composition

Properties.

Absorbed by water.

was discovered by Scheele, and has since been most ably investigated by Davy.

251. Muriatic acid gas extinguishes flame. Its specific gravity, compared with hydrogen, is = 18.5; 100 cubic inches = 39.162 grains.* 252. Muriatic acid gas is greedily absorbed by water, which takes up 480 times its bulk, and has its specific gravity increased from 1 to

1.210.

253. For saturating water with gases which are easily soluble in that fluid, we generally employ Woulfe's apparatus, one form of which is shown in the annexed cut. a, is a tubulated retort in which the materials, producing the gas or vapour, are contained; b, a receiver communicating by a bent tube with the three-necked bottle c, which is connected also by a tube with d. These bottles are about half filled with water, or any other fluid intended to be saturated with the gas; when that in c has become saturated, it passes into d, and afterwards through the tube e, which may be placed under the water, or mercury, in the pneumatic trough. In case absorption should take place in the vessels a or b, the pressure of the external air might force the water from d into c, and from e into the balloon b. This is prevented by the safety tubes ff, which dipping not more than half an inch under the surface of the water, allow a little air to enter, so as to compensate for the absorption. The different joints may be secured either by grinding, or by well-cut corks rendered tight by a mixture of drying oil and pipe-clay.

ed.

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254. When muriatic acid is thus dissolved in water, it forms the liquid muriatic acid or spirit of salt, and may easily be procured by distilling a mixture of dilute sulphuric acid and common salt, as directed in

Mow obtain- the London Pharmacopeia. The most economical proportions are 32 parts of salt, and 22 of sulphuric acid, diluted with one third its weight of water. The retort containing these ingredients may be luted on to a receiver, containing twice the quantity of water used in diluting the sulphuric acid, and the distillation carried on in a sand-bath.

255. When this liquid acid is pure it is perfectly colourless, but it generally has a yellow hue arising from a little iron. When heated, the gaseous acid is evolved.

* When the specific gravity of oxygen =1, that of muriatic acid gas will be 1.156; now to find the atom of muriatic acid, we have only to multiply its specific gravity by 4, i. e. 1.156 X4-4.625 the atom of muriatic acid, (when that of oxygen is taken=1), again the atom of muriatic acid is 37 times as great as that of hydrogen, for 0.125×37-4.625,

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256. The following Table shows the quantity of real acid contained in 100 parts of liquid acid of different specific gravities.-DAVY's Elements, p. 253.

Table showing the Quantity of real Acid in Liquid Muriatic Acid of different Specific Gravi ties. (Temperature 45° Fahr. Barometer 30.)

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257. Hydrogen and Iodine exert a slow action under ordinary cir- Hydriodie cumstances; but when iodine is presented to nascent hydrogen, they acid. readily unite, and produce a gaseous acid, the hydriodic acid. It is prepared by the action of moist iodine upon phosphorus, and must be received over mercury; which, however, soon acts upon and decomposes it, so that it should be transferred as speedily as possible into an exhausted vessel. In procuring it, it is convenient to use a small retort or bent tube, into the bulb of which is introduced the iodine, and a small stick of phosphorus placed in the neck above it, which can be shaken down upon the iodine when the beak of the tube or retort is placed under the inverted jar; a quantity of the gas is instantly and violently generated, and a further portion is obtained on applying the flame of a spirit lamp.

258. Hydriodic acid is colourless, very sour, and smells like muriatic acid*. Its specific gravity to hydrogen is as 63.00 to 1. 100 cubic inches = 133.4 grains.

259. Hydriodic gas is rapidly absorbed by water. The solution, exposed to a temperature below 260°, becomes concentrated by loss of water; at about 260° it boils, and may be distilled. The specific

• These conclusions are obtained from the fact, that, hydriodic acid is composed of equal
volumes of hydrogen and iodine vapour. The specific gravity of hydriodic acid is 3.9375
(or being =1), now four times this 15.75 the atom of this acid-again 15.75 is just 126
mes 0, 125 the atom of hydrogen, (that of oxygen being -1).

gravity of the strongest liquid acid is 1.7. It becomes dark coloured when kept, in consequence of a partial decomposition, and it readily dissolves iodine, becoming of a deep brown colour.

The liquid hydriodic acid is best prepared by passing sulphuretted hydrogen through a mixture of iodine and water; sulphur is deposited, and on heating and filtering the liquor, a pure solution of hydriodic acid is obtained, which may be concentrated by evaporation.

260. That hydriodic acid gas consists of equal volumes of hydrogen and vapour of iodine is shown by the action of mercury, which by absorbing the iodine, evolves half a volume of hydrogen from one of the gas.

It is instantly decomposed by chlorine, which produces muriatic acid and the blue vapour of iodine is rendered evident. These gases often take fire on mixture.

It consists of........ 1.56 hydrogen, 0.248 (nearly 2 atoms)

Hydriodic acid

.....

98.44

100.00

iodine, 15.625 (1 atom)

It is to be noted that Thomson in his system of chemistry gives the composition of this acid from the same data,

8.6804 15.625 (1 atom)
0.125 (1 atom)

Iodine

Hydrogen

.........

0.0694

How obtain

ed.

Properties.

SECTION II. Nitrogen.

261. THIS was first recognised as a distinct aëriform fluid, by Dr. Rutherford in 1772. (Thesis, De aere Mephitico.) It may be obtained by heating phosphorus in a confined portion of dry atmospheric air, which consists of nitrogen and oxygen; the phosphorus absorbs the latter, and the former gas remains. After repeated washing, it may be considered as pure. It may also be obtained by the action of moist sulphuret of iron upon atmospheric air.

262. 100 cubic inches of nitrogen weigh 29.625 grains; so that its specific gravity, compared with hydrogen, is as 14* to 1. It is tasteless, inodorous, and insoluble in water. It does not support combustion and is fatal to animals; hence was called azote. It is not inflammable; but when its compounds are submitted to Voltaic decomposition, it is attracted by the negative pole.

263. Nitrogen and Oxygen. -These bodies unite in four proportions, and form the compounds called,

1. Nitrous oxide. 2. Nitric oxide. 3. Nitrous acid. 4. Nitric acid.

* When the specific gravity of oxygen is taken as the standard, or =1, that of nitrogell will be 0.875, or 14 of 1; again when the atom of oxygen is made 1, or the standard then twice the specific gravity of nitrogen will be its relative atom, thus, 0875×2=1.750 atom of nitrogen.

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264. Protoxide of Nitrogen, or Nitrous Oxide, may be obtained by Nitrous oxide. heating in a glass retort over an Argand lamp, the salt called nitrate of ammonia, to a temperature of about 420°. The gas which passes off may be collected over warm water, and is nitrous oxide.* 100 cubic inches weigh 46.574 grains; its specific gravity, therefore, to hydrogen. is as 22 to 1.

The taste of this gas is sweet, and its smell peculiar, but agreeable. It is easily absorbed by water, which takes up about its own bulk, and evolves it unchanged when heated.

Its singular effects, resembling intoxication, when respired, were first ascertained by Sir H. Davy. (Researches Chemical and Philosophical, chiefly concerning Nitrous Oxide. London, 1800.) The experiment of breathing this gas, however, cannot be made with impumity, especially by those who are liable to a determination of blood to

the head.

265. Nitrous oxide supports combustion, and a taper introduced into it has its flame much augmented and surrounded by a purplish halo. Phosphorus and sulphur, when introduced in a state of vivid ignition into this gas, are capable of decomposing it, and burn with the same appearance nearly as in oxygen; but, if when put into the gas, they are merely burning dimly, they then do not decompose it and are extinguished, so that they may be melted in the gas, or even touched with a red hot wire without inflaming. Charcoal, and many of the metals, also decompose nitrous oxide at high temperatures.

266. At a red heat this gas is decomposed and converted into nitrogen and nitric oxide, undergoing at the same time an increase of bulk. For experiments of this kind the following simple apparatus may be used: It consists of two bladders, one of which is filled with the gas, and the other empty attached to the extremities of a porcelain tube which traverses the body of a furnace. The bladders are supplied with stop-cocks, and the gas is squeezed from one to the other when the tube is red hot.

267. The best analysis of this gas is effected by detonation with hy- Analysis of nie drogen; one volume of nitrous oxide requires one volume of hydrogen, trous oxide. 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

*Protox of nitrogen, when oxygen is the standard has its specific gravity=1.375; this maltuplied by 2 gives 2.75 for the atom of nitrogen, when oxygen is also the atomic standardtow 1.75 is just 22 times 0.125 (the atom of hydrogen, for the same standard.)

N

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