to effloresce. Salts have not only the property of dissolving in water, but by exposure to great heat they will melt, and they require different degrees of heat to put them in a state of fusion, as well as different quantities of water for their solution.

Many of the salts are found native, and the carbonates, sulphates, and muriates are the most frequent. Chalk, limestone, and marble, are all included in the term carbonate of lime. Few salts are more copiously disseminated than the sulphate of lime, particularly in the vicinity of Paris, and hence its name Plaster of Paris. Of the native muriates, muriate of lime occurs with rock-salt, and muriate of magnesia is found in abundance in sea-water; and muriate of soda not only exists in immense quantities in the ocean, but vast mountains in different parts of the world are entirely formed of this salt. Nitrate of potash, known by the more familiar name of nitre or salt-petre, is collected in various parts of the globe. Phosphate of lime, which is the basis of all animal bones, exists native in Hungary, and composes several entire mountains in Spain. Mountains of salt were probably formed in very remote ages, and by processes of which we can form no idea. It may be sup posed, however, that these changes have been slow and gradual, for several of the native salts exhibit marks of regularity and beauty in their crystallization, which cannot be imitated by art.

QUESTIONS.-1. To what substances is the name acid given? 2 To what do most acids owe their origin? 3. How do they form salts? 4. What is said of the division of acids? 5. How is sulphuric acid procured? 6. Muriatic acid? 7. What is carbonic acid? 8. How may you obtain carbonic acid gas? 9. What are some of the properties of this gas? 10. Why do fatal accidents often happen from the burning of charcoal? 11. How may it be destroyed at the bottom of wells? 12. What is said of the number and uses of the acids? 13. How are the different salts known from each other? 14. How may salts be separated from their water of solution? 15. To what changes are crystallized salts liable on exposure to atmospheric air? 16. What native salts are mentioned? 17. What is said of salt mountains?

SIMPLE COMBUSTIBLES.

LESSON 65.

Simple Combustibles.

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E'thers, volatile liquids formed by the distillation of some of the acids with alcohol. Al'cohol, rectified spirit of wine. It is always the same from whatever kind of spirit it is distilled: it is the purely spirituous part of all liquors that have undergone the vinous fermentation.

The combinations of sulphur are denominated sulphurets; of phosphorus, phosphurets; of carbon, carburets; of hydrogen, hydrurets; the sulphuret of iron, for instance, is the union of sulphur with iron.

Most of the simple substances are combustible, or bear some relation to combustion. Light and caloric are evolved during combustion; oxygen is the principal agent; and hydrogen, sulphur, phosphorus, carbon, and the metals, are the subjects, or the true instruments of this process, Hydrogen gas may be combined with water, sulphur, phosphorus, or with carbon. When combined with phosphorus it forms phosphuretted hydrogen gas, which takes fire whenever it comes in contact with atmospheric air. The elastic substance, which is called carburetted hydrogen gas, is carbon dissolved in hydrogen; it has likewise been called heavy inflammable air. It is this gaseous compound which has occasioned so many dreadful accidents to miners, who call it the fire-damp. This gas is procured from pit-coal by dry distillation; and from its inflammability and brilliant flame, it has been used for lighting streets, shops, manufactories, and light-houses on the sea-coast. The rate at which it is procured is trifling compared to the expense of oil and tallow.

Phosphorus is a solid inflammable substance, which burns at a very low temperature, when in contact with oxygen gas or atmospheric air. Many amusing experiments may be performed with it, but it must be handled with extreme caution. If you fix a piece of solid phosphorus in a quill, and write with it upon paper, the writing, in a dark room, will be beautifully luminous. If the face or hands be rubbed with phosphuretted ether, they will appear, in a dark place, as though on fire, without danger or sensation of heat.

Pure carbon is known only in the diamond; but carbon in the state of charcoal may be procured by heating to red

ness a piece of wood closely covered with sand in a crucible, so as to preserve it while in the fire, and afterwards, while cooling, from the action of the atmosphere. It is capable of forming various combinations, but charcoal is that with which we are most familiar. Carbon is not only a component part, but it forms nearly the whole of the solid basis of all vegetables, from the most delicate flower in the garden to the huge oak of the forest. It not only constitutes the basis of the woody fibre, but is a component part of sugar, and of all kinds of wax, oils, gums, and resins, and of these again, how great is the variety! It is imagined that most of the metals may be combined with carbon; but at present we know only of its combination with iron. In one proportion it forms cast iron; in another, steel; and in a third, plumbago, generally, though improperly, called black lead. There is no lead in its composition. Cast iron contains about one forty-fifth of its weight of carbon,-steel is combined with about one part of carbon in two hundred of iron,—and plumbago, or carburet of iron, has been found to consist of nearly. nine parts of carbon to one of iron. Wrought iron differs from cast iron, in being deprived of its carbon and oxygen, by continued heat and repeated hammering, which render the metal malleable. Steel is made of wrought iron by various processes, whereby the metal resumes a small portion of the carbon, and acquires a capacity of receiving different degrees of hardness.

The metals are generally procured from beneath the surface of the earth, in a state of combination either with other metals, with sulphur, oxygen, or with acids; though a few of them have occasionally been found in a state of purity. Metals are the great agents by which we are enabled to examine the recesses of nature; and their uses are so multiplied, that they are become of the greatest importance in every occupation of life. They are the instruments of all our improvements, of civilization itself, and are even subservient to the progress of the human mind towards perfection. They differ so much from each other, that nature seems to have had in view all the necessities of man, in order that she might suit every possible purpose his ingenuity can invent, or his wants require. We not only receive this great variety from the hand of nature, but these metals are rendered infinitely valuable by various other properties they

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 oxygen 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 Iodides, Chlori des; 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

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 exquisitely 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 gas is decomposed, and its oxygen combines with the ignited