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and variety of the globe which we inhabit. In its solid state, we are familiar with it, in the form of blocks of ice, of sleet and hail, of hoar-frost fringing every shrub and blade of grass, or of snow protecting the tender plant, as with a fleecy mantle, from the piercing frosts of winter. The rare but splendid spectacles of mock suns, or parhelia, are due to the refractive power of floating spiculæ of ice upon the sun's rays. In its liquid condition, as rain or dew, it bathes the soil; and the personal experience of all will testify to the charm which the waterfall, the rivulet, the stream, or the lake, adds to the beauty of the landscape; whilst few can behold unmoved the unbounded expanse of ocean, which, whether motionless, or heaving with the gently undulating tide, or when lashed into fury by the storm which sweeps over its surface, seems to remind man of his own insignificance, and of the power of Him who alone can lift up or quell its roaring waves. In vapor, how much variety is added to the view by the mist or the cloud, which, by their ever-changing shadows, diversify, at every movement, the landscape over which they are fitting; whilst the gorgeous hues of the clouds around the setting sun, and the glowing tints of the rainbow, are due to the refractive action of water and watery vapor upon the solar rays.'

NITROGEN.

28. Preparation of Nitrogen. -Pure nitrogen may be readily prepared by passing a stream of chlorine gas through strong aqua ammonia. It is well to pass the nitrogen through a wash-bottle, to remove the white fumes, which, as we have seen (3), are a compound of hydrogen and nitrogen. The apparatus used is shown in

* Miller's Elements of Chemistry, Part II. pp. 35, 36.

Figure 1o. The chlorine is generated in the flask at the left; the ammonia is put in the next bottle ; and the nitro

Fig. 10.

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gen is washed in the third bottle, by being made to bubble up through water.

29. Properties of Nitrogen. - Nitrogen is a colorless gas, and is a little lighter than air. Its chief characteristic is its inertness. We have already seen (3) that it neither burns nor allows a taper to burn in it.

30. Nitric Oxide. Put some bits of copper into a bottle (Figure 11), and add aquafortis or nitric acid. A

Fig. 11.

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reddish gas fills the upper part of the bottle, and passes off through the tube. When collected over water, it is colorless. The red color was owing to impurities, which have been absorbed by the water.

Invert a jar of this gas over a piece of well-lighted phosphorus, and the latter burns almost as brilliantly as in oxygen, filling the jar with white fumes of phosphoric anhydride (phosphoric acid.) The experiment proves the presence of oxygen in the gas in which the phosphorus was burned.

Pass a mixture of equal parts of this same gas and hydrogen through a tube containing some heated platinized asbestos, and hold a piece of moistened red litmuspaper at the mouth of the tube. The paper is turned blue, showing that ammonia has been produced; for ammonia is the only gas that turns red litmus-paper blue. We have seen (3) that ammonia is a compound of hydrogen and nitrogen ; therefore there must have been nitrogen in the gas mixed with the hydrogen.

The gas is, in fact, a compound of nitrogen and oxygen, and is called nitric oxide (deutoxide or binoxide of nitrogen), and its symbol is NO.

31. Catalysis. - In the above experiment the platinized asbestos remains wholly unchanged. By its mere presence, it has made the hydrogen unite with the elements of the gas mixed with it. This remarkable action by mere presence is called catalysis. It occurs in many other cases, but is very imperfectly understood.

32. Nascent State. Nitrogen, as we have seen, is a very inert substance. Indeed, it can be made to combine directly with scarcely any element. In the above experiment, the hydrogen first seizes upon the oxygen, forming water, and sets the nitrogen free.

At the moment when it is thus set free it has an increased activity, and readily unites with the hydrogen to form ammonia.

It is found generally true that elements are unusually active when just liberated from compounds. They are then said to be in the nascent state.

33. Nitrous Anhydride. -- If a jar of oxygen be inverted over a jar of nitric oxide, the gases, on mixing, become of a bright cherry-red color. The compound formed differs from nitric oxide only in containing more oxygen.

It is called nitrous anhydride (nitrous acid), and its formula is N,Og.

34. Nitric Peroxide and Nitric Anhydride. — It is possible to form two higher oxides of nitrogen, NO2, nitric peroxide, and NGOs, nitric anhydride.

The former, at a temperature below 70°, is an orangecolored liquid ; and the latter is a white solid, which eagerly unites with water, forming the well-known

aquafortis, or nitric acid, HNO. The reaction between nitric anhydride and water is shown by the following equation :

} (H2O + N2O3)=HNOz. 35. Nitric Acid. - Nitric acid is a strongly fuming liquid, colorless when pure, but usually yellowish from the presence of some of the lower oxides of nitrogen. It is one of the most corrosive substances known, and rapidly destroys all animal substances. When diluted, it stains the skin, wool, feathers, and the like, a bright yellow color, and is often used as a permanent yellow dye for silk and woollen goods. It acts violently upon tin and iron filings, especially when they are moistened with water. Indeed it attacks all the ordinary metals, except gold and platinum. Its action upon them, however, is more energetic when it is somewhat dilute.

The action of nitric acid upon the metals is owing to the readiness with which it parts with some of its oxygen. It first oxidizes them, and then acts upon these

basic oxides (16), to form salts (17). During this process, the lower oxides of nitrogen are always given off, as is indicated by the appearance of red fumes.

Nitric acid may be made on a small scale by heating potassic nitrate (saltpetre), in a retort with sulphuric acid (oil of vitriol). The nitric acid distils over, and is collected in a receiver. The re-action is as follows:

2KNO, +H,80,=K,50 + 2HNO3. The hydrogen and the potassium change places, giving rise to potassic sulphate (sulphate of potash) and nitric acid.

On the large scale, iron retorts, coated with fire-clay on the inside of the upper part, where they are exposed to the acid vapors, are employed for the distillation, and sodic nitrate (soda saltpetre) is substituted for potassic nitrate, as it is a cheaper salt, and likewise yields 9 per cent more nitric acid than potassic nitrate.

36. Nitrous Oxide. - A fifth oxide of nitrogen is obtained by gently heating ammonic nitrate (nitrate of ammonia). It is called nitrous oxide, and its symbol is N,O. The reaction is shown by the following equation :

(H.N)NO, = 2H,O+N,O. The ammonic nitrate, (H N)NO3, breaks

up

into water and nitrous oxide.

N,O is a colorless gas, and readily gives up its oxygen. Phosphorus burns in it as brilliantly as in pure oxygen. A splint of wood with a sp rk on the end of it bursts into flame when plunged into the gas. When inhaled, it has a peculiarly exhilarating effect, and hence is called laughing gas. It is used by dentists as an anæsthetic, since it makes the patient for the time insensible to pain. Great care must be taken that the gas when inhaled is perfectly pure.

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