Carbonate

“ Estimation of the Actual Calcium Carbonate.—The lime which is found in the state of carbonate plays one of the most important rôles in the chemical phenomena which take place in the soil. It is often of great importance to determine it. The most certain process is to estimate the carbon dioxid which is disengaged from the carbonate under the influence of an acid and to receive this gas in a jar graduated to measure it by volume. The flask recommended by the French Commission for this purpose contains about 300 cubic centimeters. ”

“ It exists in various natural bodies in which carbon and oxygen are combined; it is evolved by the decomposition of numerous bodies called carbonates, in which carbon is united with a particular base, such as the carbonate of lime, the carbonate of iron, the carbonate of copper, &c. It is also evolved by the processes of fermentation, by the breathing of animals, the combustion of fuel, and the functions of plants. Carbonic acid also exists in various waters. ”

“ If the earth contain carbonate, however, it is necessary to add the fuming acid in small portions of about five cubic centimeters at a time, waiting each time until the disengagement of the gas caused by the previous addition has ceased. A soil which contains from thirty to forty per cent of calcium carbonate should be carefully treated in a porcelain capsule with a slight excess of sulfuric acid, pure and dilute. The mixture is afterward to be evaporated to dryness upon a sand-bath and the residue heated in a drying oven to 110°. ”

“ In specific gravity, it scarcely differs from distilled water. It nevertheless generally holds in solution common air, carbonic acid, carbonate of132 lime, chloride of lime, and a trace of nitric acid. If it be collected from the roofs of houses, after it has rained for some time, it contains sulphate of lime and occasionally carbonate of lead. The quantity of common air in rain water does not exceed 31⁄2 cubic inches in 100 cubic inches of water; it contains more oxygen than atmospherical air; the same quantity of rain water contains one inch of carbonic acid gas. ”

“ It is less volatile and pungent than the neutral carbonate; soluble in 4 parts of water at 55° Fahr., 3·3 parts at 62°, 2·5 parts at 96°, and 2 parts at 120°; boiling water and alcohol decompose it, with the evolution of carbonic acid gas and ammonia; by age or exposure to air, the surface assumes an opaque white colour, from its carbonate flying off, and the remaining bicarbonate being less volatile. Unlike the carbonate, it can neither be resublimed nor digested or distilled with either alcohol or water, without suffering decomposition. Sp. gr. ”

“ The carbonates form a very important class of salts. They are found in large quantities in nature, and are often used in chemical processes. Only the carbonates of sodium, potassium, and ammonium are soluble, and these can be made by the action of carbon dioxide on solutions of the bases, as has just been explained.
The insoluble carbonates are formed as precipitates when soluble salts are treated with a solution of a soluble carbonate. Thus the insoluble calcium carbonate can be made by bringing together solutions of calcium chloride and sodium carbonate:
CaCl2 + Na2CO3 = CaCO3 + 2NaCl. ”

“ It is afterwards treated with dilute nitric acid to dissolve the calcium carbonate. When the carbonate is abundant, it is sufficient to determine it by difference which is done by washing the material, drying and weighing. But when the proportion of carbonate is very small and in consequence when its exact determination acquires a greater importance, it is better to determine the lime directly. For this purpose the part soluble in dilute nitric acid is collected, treated with ammonia and acetic acid and precipitated with ammonium oxalate. ”

“ Most of the earthy carbonates are found abundantly in nature. In general the salts of this class may be formed by adding an alkaline carbonate to a salt of the metal in solution by double decomposition.
Prop. The carbonates of the alkalies are soluble in water; those of the other bases are for the most part insoluble, except the water is highly charged with carbonic acid. From most of them carbonic anhydride or anhydrous carbonic acid can be easily expelled by heat. ”

“ The carbonate, being insoluble in strong alcohol (and many other liquid organic compounds) , is much used for dehydration of the corresponding aqueous preparations. The pure carbonate is constantly used in the laboratory as a basic substance generally, for the disintegration of silicates, and as a precipitant. The industrial preparation serves for the making of flint glass, of potash soap (soft soap) and of caustic potash. Potassium bicarbonate, KHCO3, is obtained when carbonic acid is passed through a cold solution of the ordinary carbonate as long as it is absorbed. ”

“ After cooling thoroughly, the cold basic acetate, which may now have crystallised or separated out more or less, according to the strength of the solution, is treated with carbonic acid gas, whereby the basic acetate, in the presence of the ammonia set free, is converted into basic carbonate of lead of exceptionally white colour, and with high basicity and covering power, proper care being taken as specially indicated later on. ”

“ There it is, you see—that is to say, the carbonate lime, which results from carbonic acid, and that carbonic acid must be formed from the carbon which comes from the wood, from the candle, or any other thing. Indeed, you have yourselves frequently tried a very pretty experiment, by which you may see the carbon in wood. If you take a piece of wood, and partly burn it, and then blow it out, you have carbon left. There are things that do not shew carbon in this way. A candle does not shew it, but it contains carbon. Here also is a jar of coal-gas, which produces carbonic acid abundantly. ”

“ Of sodium and potassium hydroxide, it may be said that they can be used with all indicators, and their solutions may be boiled, but they absorb carbon dioxide readily and attack the glass of bottles, thereby losing strength; sodium carbonate may be weighed directly if its purity is assured, but the presence of carbonic acid from the carbonate is a disadvantage with many indicators ”

“ Most other carbonates are formed by precipitation of salts of the metals by means of alkaline carbonates. All carbonates, except those of the alkali metals and of thallium, are insoluble in water; and the majority decompose when heated strongly, carbon dioxide being liberated and a residue of an oxide of the metal left. The alkaline carbonates undergo only a very slight decomposition, even at a very bright red heat. The carbonates are decomposed by mineral acids, with formation of the corresponding salt of the acid, and liberation of carbon dioxide. ”

“ If the quantity of carbonic acid diminishes, the bicarbonate of the water is decomposed, half of its carbonic acid escapes into the atmosphere, and the neutral carbonate of lime is precipitated. The aqueous vapor condensed from the air dissolves part of the carbonic acid contained therein, and carries it along, when it falls as rain upon the earth, and takes up there enough lime to form the bicarbonate, which is thus carried back to the sea. ”

“ Their formula in Na2CO3, 10H2O, corresponding to 37% of dry sodium carbonate. They are made by dissolving ordinary soda-ash in hot water, adding a small quantity of chloride of lime for the destruction of colouring matter and the oxidation of any ferrous salts present, carefully settling the solution, without allowing its temperature to fall below the point of maximum solubility (34 deg. C.) , and running the clarified liquid into cast-iron crystallizers or ``cones,'' where, on cooling down, most of the sodium carbonate is separated in large crystals of the decahydrated form. ”

“ Mix the precipitate, without drying it, with a gallon of water, and force carbonic-acid gas into it under strong pressure, till a complete solution is effected. The Eau Magnésienne of the French codex is about a third of this strength; and we have met with some prepared in this country not much stronger.
Carbonated Lime Water. Carrara water. Lime water (prepared from lime made by calcining Carrara marble) is supersaturated by strong pressure with carbonic acid, so that the carbonate of lime at first thrown down is redissolved. It contains 8 gr. of carbonate of lime in 10 fl. oz. ”

“ Carbon is found in nature in the uncombined state in several forms. The diamond is practically pure carbon, while graphite and coal are largely carbon, but contain small amounts of other substances. Its natural compounds are exceedingly numerous and occur as gases, liquids, and solids. Carbon dioxide is its most familiar gaseous compound. Natural gas and petroleum are largely compounds of carbon with hydrogen. The carbonates, especially calcium carbonate, constitute great strata of rocks, and are found in almost every locality. ”

“ Carbon is an element widely distributed in nature, occasionally appearing in its elementary form, as graphite or the diamond, but much more important in its compounds. Small quantities are present in the air as carbon dioxide, CO2, immense quantities occurring in the carbonate minerals, which have been considered under their respective metallic salts, as calcite, malachite, siderite, cerrusite, smithsonite, witherite, etc., and still other large quantities being represented in organic compounds, which occur as rocks under the heads of petroleum, coal, etc. ”

“ Carbonic acid occurs in nature, combined with many salifiable bases; as in the carbonates of soda, baryta, strontia, magnesia; the oxides of iron, manganese, zinc, copper, lead, &c. From these substances it may be separated, generally speaking, by strong ignition, or, more readily, by the superior affinity of muriatic, sulphuric, or nitric acid, for the earth or metallic oxide. It is formed whenever vegetable or animal substances are burned with free access of air, from the union of their carbonaceous principle with atmospheric oxygen. ”

“ A large exposure of land surface is correlated with a rapid solution of calcium and magnesium carbonates, which, becoming bicarbonates, represent a loss of carbonic acid to the atmosphere. On the other hand, the formation of the normal carbonate by lime-secreting animals causes a direct liberation of the second equivalent of the bicarbonate. Therefore extensive oceans and abundant marine life are correlated with warm climate. ”

“ The Neva contains 40 parts of calcium carbonate per 100 parts of saline matter. The considerable amount of calcium carbonate which river water contains is very easily explained from the fact that water which contains carbonic acid in solution easily dissolves calcium carbonate, which occurs all over the earth. Besides calcium carbonate and sulphate, river water contains magnesium, silica, chlorine, sodium, potassium, aluminium, nitric acid, iron and manganese. ”

“ When the sulphuric acid is permitted to unite with the chalk and water, carbonic acid is liberated. A boy turning a wheel forces the gas into the water in the bottles, or the water and carbonate of soda is drawn off thus impregnated into bottles and corked down, in the manner so familiar to all. ”

“ From these we may well conclude that enormous variations have occurred, but not that the variation has always proceeded in the same direction.
“Carbonic acid is supplied to the atmosphere by the following processes:— (1) volcanic exhalations, and geological phenomena connected therewith; (2) combustion of carbonaceous meteorites in the higher regions of the atmosphere; (3) combustion and decay of organic bodies; (4) decomposition of carbonates; (5) liberation of carbonic acid mechanically inclosed in minerals on their fracture or decomposition. ”

“ The solvent power which holds all these solid substances in solution, and which contributes to their agreeable taste, is the carbonic acid gas with which the water is so freely charged. This free carbonic acid gas is probably formed by the decomposition of the carbonates which compose the rock. The water, impregnated with it, becomes a powerful solvent, and, passing through different strata, absorbs the various mineral substances which compose its solid constituents. ”

“ From two to ten grams of earth are employed, according to its richness in organic matter. The total carbon dioxid is obtained in this process both from carbonates and organic bodies. The water and carbon dioxid are secured and weighed in the usual manner.
The oxygen method should be used in all cases possible. Although it does not always give the whole of the carbon dioxid present as carbonates, the rest can be easily estimated by treating the residue in the boat with hydrochloric acid, in an apparatus for estimating that gas. ”

“ It has often been suggested that, during the Carboniferous period, the atmosphere must have been warmer and more charged with aqueous vapour and carbon dioxide than at the present day, to admit of so luxuriant a flora as that from which the coal-seams were formed. There seems, however, to be at present no method of arriving at any certainty on this subject. Lastly, the amount of carbonic acid absorbed in the weathering of rocks at the surface, and the consequent production of carbonates, represents an enormous abstraction of this gas. ”