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possess by their combustibility, their solubility in fluids, their combinations with various substances, and by their union with each other, whereby compounds or alloys are formed, extremely useful in a variety of arts, manufactures, and other requisites of life. By combining them with oxy gen we can invest them with new properties, and are enabled to employ these to promote the progress of the fine arts, by imitating the master-pieces of creation in the production of artificial salts, gems, and crystals, of every colour and of every shade.

QUESTIONS.-1. What are the simple combustibles? 2. What is said of phosphorus combined with hydrogen gas? 3. What is carburetted hydrogen gas? 4. What do miners call it? 5. To what use may it be applied? 6. What is phosphorus? 7. What experiments may be performed with it? 8. How may carbon be obtained in the state of charcoal? 9. What is said of carbon with regard to vegetables, sugar, wax, &c. 10. What is said of its combinations with iron? 11. In what state are metals generally found? 12. What is said of the utility of metals? [NOTE. Chlorine (oxymuriatic acid,) boron and fluorine (the bases of the boric and fluoric acids,) and a substance of recent discovery, called iodine, have lately been added to the list of simple substances. (see Appendix.) Iodine and Chlorine are capable of forming distinct and peculiar acids by combination with Hydrogen. They form various other compounds, such as lodides, Chlorides; Iodates, Chlorates; Iodurets, Chlorurets, &c.

LESSON 66.

Oxyds and Combustion.

As oxygen can combine in different proportions with the same simple substance, the products have been designated by the names of protoxyd, deutoxyd, or tritoxyd, according as the oxygen entered into it, in one, two, or three proportions; and that has been called peroxyd, which was most oxydated, or oxydized. Retort', see description of fig. 48, in Appendix.

ANY metal or combustible body which is combined with less oxygen than is sufficient to render it acid, is usually called an oxyd. Whenever a substance is converted into an oxyd, we say it is oxydized; but if it becomes an acid by its union with oxygen, we say it is oxygenized. The mineral, the animal, and the vegetable kingdoms, all furnish matters which are convertible into oxyds, by an union with oxygen. Metallic oxyds are formed in several ways, the chief

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of which are by the access of atmospheric air, by the decomposition of water, and by the decomposition of acids. Iron may be mentioned as a familiar example of a metal becoming oxydized by atmospheric air. It is well known that when this metal is exposed to air and moisture, it acquires rust, or in other words its surface is converted to an oxyd, in which state the metal will be found to have acquired an increase of weight. Common red lead, which is a true oxyd of lead, is made by melting that metal in ovens so constructed as to have a free access to atmospheric air. Gold, silver, and platina, cannot be oxydized, unless in a very high temperature; and with respect to other metals, they not only differ in their capacity for oxygen, but also in their attraction for it; so that one will often rob the other, thus reducing the first oxyd to its primitive metallic form. If you dissolve some quicksilver in nitric acid, and after dropping a little of the solution upon a bright piece of copper, gently rub it with a piece of cloth, the mercury will precipitate itself upon the copper, which will be completely silvered,

With regard to the oxyds of nitrogen; the first degree of oxydizement produces nitrous oxyd;-a further portion of oxygen nitric oxyd, and they are both in a state of gas. Nitrous oxyd gas bears the nearest resemblance of any other to atmospheric air. It will support combustion even better than common air; it is respirable for a short time, and it is absorbed by water. Persons who have inhaled this gas have felt sensations similar to those produced by intoxication. In some people it produces involuntary muscular motion and a propensity to leaping and running; in others, involuntary fits of laughter; and in all, high spirits, and the most exquisite ly pleasurable sensations, without any subsequent feelings of debility. It is readily procured by exposing crystals of nitrate of ammonia, in a retort, to the heat of a lamp, by which means, the ammoniacal salt is decomposed, and this gas is evolved.

Combustion may be defined to be a process by which certain substances decompose oxygen gas, absorb its base, and suffer its caloric to escape in the state of sensible heat. The agency of oxygen in combustion is attributable to its affinity for combustible bodies. The combustible having a greater affinity to oxygen than oxygen has to caloric, the oxygen as is decomposed, and its oxygen combines with the ignited

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body, while its caloric, becoming free, is diffused among the surrounding bodies. Whenever we burn a combustible body, a continued stream of atmospheric air flows towards the fire place, to occupy the vacancy left by the air that has undergone decomposition, and which, in its turn, becomes decomposed also. Hence a supply of caloric is furnished without intermission, till the whole of the combustible is saturated with oxygen. As the combustible burns, light is disengaged, and the more subtile parts, now converted by caloric into gas, are dissipated in that state. When the combustion is over, nothing remains but the earthy parts of the combustible, and that portion which is converted, by the process, into an oxyd, or an acid. The smoke which arises from a common fire is chiefly water in the state of vapour, with a mixture of carburetted hydrogen and bituminous substances; part of the water comes from the mosture of the fuel; the other part is formed during combustion, by the union of the hydrogen of the combustible with the oxygen of the atmosphere. The agency of oxygen in combustion may be demonstrated by placing a lighted candle under a glass vessel inverted upon a plate of water. will be seen that the candle will go out as soon as it has consumed all the oxygen contained in the included air, and that the water will rise up in the vessel to fill the vacancy. In the decomposition of atmospheric air by combustion, it is natural to ask what becomes of the nitrogen gas? As the oxygen becomes fixed in the combustible body, its caloric is disengaged, a part of which combines with the nitrogen, and carries it off in the form of rarefied nitrogen gas. When bodies are burnt, none of their principles are destroyed. We have reason to think that every particle of matter is indestructible, and that the process of combustion merely decomposes the body, and sets its several component parts at liberty, to separate from each other, to form other new and varied combinations. It was said of old, that the Creator weighed the dust, and measured the water, when he made the world. The first quantity is here still; and though man can gather and scatter, move, mix, and unmix, yet he can destroy nothing: the dissolution of one thing is a preparation for the being, and the bloom, and the beauty of another, Something gathers up all the fragments, and nothing is lost.

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QUESTIONS.-L. What is an oxyd? 2. What are the principal ways by which metallic oxyds are formed? 3. What is said of iron as an example? 4. What is red lead and how is it made? 5. What is said of ueferent capacity and attraction of metals for oxygen? 6. What experiment is given for illustration? 7. What is said of the properties of nitrous oxyd gas? 8. What effects does it produce on being inhaled? 9. How may it be procured? 10. How may combustion be defined? 11. How is the process of combustion explained? 12. What remains when the combustion is over? 13. What is smoke? 14. How may the agency of oxygen in combustion be demonstrated? 15. What becomes of the nitrogen gas? 16. What is said of the indestructibility of matter? 17. What is a retort? (see Appendix.) 18. How may chlorine be procured? 19. What is said of the attraction of chlorine for the metals? 20. How is combustion defined in the Appendix, and on what grounds is it so defined?

LESSON 67.

Electricity.

Electric. The first electrical phenomena are supposed to have been observed in a mineral substance called araber, in Greek elektron, and hence the fluid or power has been denominated electric.

THE surface of the earth, and of all the bodies with which we are acquainted, is supposed to contain or possess a power of exciting or exhibiting a certain quantity of an exceedingly subtile agent, called the electric fluid or power. The quantity usually belonging to any surface, is called its natural share, and then it produces no sensible effects; but when any surface becomes possessed of more, or of less, than its natural quantity, it is electrified, and it then exhibits a variety of peculiar and surprising phenomena ascribed to the power called electric. If you take a stick of sealing-wax and rub it on the sleeve of your coat, it will have the power of attracting small pieces of paper, or other light substances, when held near them. If a clean and dry glass tube be briskly rubbed with the hand, or with a piece of flannel, and then presented to any small light substances, it will immediately attract and repel them alternately for a considerable time. The tube is then said to be excited. If an excited glass tube, in a dark room, be brought within about half an inch of the finger, a lucid spark will be seen between the finger and the tube, accompanied with a snapping noise, and a peculiar sensation of the finger. Dry flannel clothes,

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when handled in the dark, frequently exhibit a sparkling appearance, attended with the same kind of noise that is heard in the experiment of the glass tube.

All those bodies which transmit or conduct electricity from one surface to another, are called conductors, and those surfaces that will not transmit the electric power, are called electrics or non-conductors. The general class of conductors comprehends metals, ores, and fluids in their natural Vitrified and resinous substances, state, except air and oils. amber, sulphur, wax, silk, cotton, and feathers, are electrics or non-conductors. Many of these, such as glass, resin, When a surand air, become conductors by being heated. face is supposed to have more than its natural quantity of this fluid, it is said to be positively electrified; and when less than its natural share, to be negatively electrified. When any electrified conductor is wholly surrounded by non-conductors, so that the electric fluid cannot pass from it along conductors to the earth, it is said to be insulated. The human body is a good conductor of electricity; but if a person stand on a cake of resin, or on a stool supported by glass legs, the electric fluid cannot pass from him to the earth, and if he is touched by another person standing on the ground, the same sparkling appearance and noise, as mentioned above, will be exhibited. Two surfaces, both positively, or both negatively electrified, repel each other; and two substances, of which one is positively, and the other negatively electrified, attract each other. Opposite electricities always accompany each other, for if any surface become positive, the surface with which it is rubbed becomes ́negative; and if any surface be rendered positive, the nearest conducting surface will become negative. When one side of a conductor receives the electric fluid, its whole surface is instantly pervaded; but when an electric or nonconductor is presented to an electrified body, it becomes electrified on a small spot only. If to one side of a pane of glass, you communicate positive electricity, the opposite side will become negatively electrified, and the plate is then said to be charged. These electricities cannot come together, unless a communication, by means of conductors, is made between the sides of the glass; and if their union be made through the human body, it produces an affection of the nerves called an electric shock.

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