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Acids which contain different quantities of oxygen are distin-
guished by their termination. The name of that which con-
tains most oxygen ends in ic, the other in ous.
Thus we say
sulphuric acid, and sulphurous acid. All salts that are com-
posed of acids ending in ic, take an ending in ate; as sulphate
of lime, a compound of lime with sulphuric acid. All salts
composed of acids ending in ous, take an ending in ite, in-
stead of ate; as sulphite of lime. When there is an excess
of acid, the preposition super is added; and when an excess of
the base, then sub is prefixed, as super-sulphate of potash, or
sub-borate of soda, (borax.)

THE name acid, in the language of chemists, has been given to all substances, whether liquids or solids, which produce that sensation on the tongue which we call sour. Most of the acids owe their origin to the combination of certain substances with oxygen; and they have the property of changing the blue, green, and purple juices of vegetables to red, and of combining with alkalies, earths, or metallic oxyds, so as to compose those compounds termed salts. The acids were formerly divided into three classes, mineral, vegetable, and animal; but the more useful and scientific way of dividing them is into two classes only. The undecomposable acids, and those which are formed with two principles, are comprised in the first class; while those acids which are formed with more than two principles compose the second class.

Sulphuric acid is procured by burning sulphur, in contact with some substance containing oxygen; by which process the sulphur combines with the oxygen, and becomes acidified. In commerce it is commonly called the oil of vitriol. That peculiar acid which is called muriatic is usually obtained from muriate of soda, which is the chemical name for common salt. Carbonic acid is a combination of carbon and oxygen. It was formerly called fixed air, on account of its being so intimately combined in chalk, lime-stone, and other substances. If you pour some diluted sulphuric acid over pulverized chalk or marble contained in a glass vessel, which has a tube connected with it, an effervescence will take place, and carbonic acid gas will escape through

the tube.

This gas is more destructive of life than any

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other, and it extinguishes flame instantaneously. Water may be made by pressure to absorb three times its bulk of this gas; by which it acquires an acidulous and not unpleasant taste. Soda water, cider, and other fermented liquors owe their briskness and sparkling to the presence of this gas. Fatal accidents often happen from the burning of charcoal in chambers, for wherever charcoal is burned this gas is always formed. It so often occupies the bottoms of wells, that workmen ought not to venture into such places without previously letting down a lighted candle. If the candle burns they may enter it with safety; if not, a quantity of quick-lime should be let down in buckets, and gradually sprinkled with water. As the lime slakes, it will absorb the gas, and the workmen may afterwards descend in safety.

The number of acids that are well known amounts to more than forty, and their uses are so many and important that it is impossible to enumerate them. They are indispensable to various arts and manufactures; they are employed for culinary purposes, and for medicine; they act an important part in the great elaboratory of nature, and form a great proportion of many of the mountainous districts of the globe in their various combinations.

The precise number of the salts is not known, but they probably amount to more than two thousand. The different salts are known from each other by the peculiar figure of their crystals, by their taste, and other distinctive or specific characters. The separation of salts from the water in which they may be dissolved, is generally effected by evaporation and cooling. When a certain portion of the water of solution is evaporated, and the remainder left in a proper temperature at rest, the salts will shoot into crystals, and will be found dispersed through the water at the bottom and at the sides of the vessel, and sometimes also on the surface of the solution. Their crystallization is owing to the abstraction of the heat or water by which they were dissolved. Crystallized salts are liable to changes in their appearance by exposure to atmospheric air. Some have so great an af finity for water that they absorb it with avidity from the atmosphere, and thus becoming moist or liquid, they are said to deliquesce. Others, having less affinity for water than atmospheric air has, lose their water of crystallization by exposure, and readily fall into powder. Such salts are said

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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 supposed, 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 proper. ties 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.

143

LESSON 65.

Simple Combustibles.

E'thers, volatile liquids formed by the distillation of some of the acids with alcohol. Alcohol, 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

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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 or der 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

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