Carbonic acid

“ Carbonic acid is soluble in water, and at the ordinary pressure and temperature one volume of water will hold in solution one volume of the gas; under increased pressures, far larger quantities of the gas can be held in solution, but this is rapidly evolved as soon as the excess of pressure is removed. Upon this property the manufacture of aerated waters depends. The presence of free carbonic acid can be easily detected by causing the gas to pass over the surface of some clear lime-water. If any be present a white film of carbonate of lime will at once be formed. ”

“ The particles of the carbonic acid being so closely approximated in the solid, the whole force of cohesive attraction (which in the fluid is weak) becomes exerted, and opposes its tendency to assume its gaseous state; but as it receives heat from surrounding bodies, it passes into gas gradually and without violence. The transition of solid carbonic acid into gas deprives all around it of caloric so rapidly and to so great an extent, that a degree of cold is produced immeasurably great, the greatest indeed known. ”

“ Carbonic acid exists in the atmosphere; it is given off from the lungs of all living animals while they breathe; it is also produced largely during the burning of wood, coal, and all other combustible bodies, so that an unceasing supply of this gas is poured into the air. Decaying animal and vegetable substances also give off this gas, and hence it is always present in greater or less abundance in the soil, and especially in such soils as are rich in vegetable matter. ”

“ Carbonic acid is colorless and inodorous, but has a peculiar sharp taste; it is half as heavy again as air, its exact specific gravity being 1529; one hundred cubic inches weigh 47.26 grains. It is uninflammable, and does not support combustion or animal respiration. Under a pressure of about 38 atmospheres, at a temperature of 32° F., carbonic acid condenses into a colorless liquid, which may also be frozen into a compact mass resembling ice, or into a white powder like snow. ”

“ We all know how dangerous acid is in water, causing that water to act on many substances, the iron of iron vessels, the lime in soil or rock, etc., bringing iron and lime respectively into solution. Now the atmosphere contains carbonic acid, and carbonic acid occurs in the earth, being evolved by decomposing vegetation, etc. Carbonic acid is also soluble to a certain, though not large extent, in water. As we shall see, water charged with carbonic acid attacks certain substances insoluble in pure water, and brings them into solution, and thus the water soon becomes hard. ”

“ If we pass the above-mentioned processes for consuming and producing carbonic acid under review, we find that they evidently do not stand in such a relation to or dependence on one another that any probability exists for the permanence of an equilibrium of the carbonic acid in the atmosphere. ”

“ The carbonic acid of the air is consumed chiefly by the following processes: (6) formation of carbonates from silicates on weathering; and (7) the consumption of carbonic acid by vegetative processes. The ocean, too, plays an important role as a regulator of the quantity of carbonic acid in the air by means of the absorptive power of its water, which gives off carbonic acid as its temperature rises, and absorbs it as it cools. ”

“ Carbonic acid can be prepared for experimental purposes by causing dilute hydrochloric acid to act upon fragments of marble placed in a bottle with two necks, into one neck of which a funnel passing through a cork is fixed, and into the other a bent tube for conveying the gas into any suitable receiver. ”

“ One often hears the opinion expressed, that the quantity of carbonic acid in the air ought to have been very much greater formerly than now, and that the diminution should arise from the circumstance that carbonic acid has been taken from the air and stored in the Earth's crust in the form of coal and carbonates. ”

“ 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. ”

“ The following table shows how much carbonic acid artificial lights produce per hour:
A five-foot gas-burner produces as much carbonic acid per hour as five men.
As the most poisonous element of the breath can not readily be detected by analysis, the amount of carbonic acid is taken as a measure of the impurity of air contaminated by respiration.
Test for carbonic acid in air (Pettenkofer’s method) :
Shake up a definite volume of the air in a closed [Pg 10] vessel with a definite amount of lime-water. The carbonic acid unites with the lime, forming carbonate of lime. ”

“ Why carbonic acid is, to a limited degree, given off by the plant in the night, is merely because the vital process, or the fixation of carbon and evolution of oxygen, ceases when the light is withdrawn. The plant is only in a passive state. Ordinary chemical forces resume their sway, and the oxygen of the air combines with the newly deposited carbon to reproduce a little carbonic acid. But this must be placed to the account of decomposing, not of growing vegetation; for by so much as plants grow, they decompose carbonic acid and give its oxygen to the air, or, in other words, purify the air. ”

“ Carbonic acid gas has so strong an attraction for all the alkalies and alkaline earths, that these are always found in nature in the state of carbonats. Combined with lime, this acid forms chalk, which may be considered as the basis of all kinds of marbles, and calcareous stones. ”

“ 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. ”

“ Carbonic acid is indeed produced in a great variety of ways, besides by animals in breathing, and fuel in burning. It is remarkable that it is only the green parts of plants which breathe as has been described; the leaves and stems giving out oxygen, and absorbing carbonic acid. The flowers and the ripe fruits of plants act on the air in the same way as animals, and hence deteriorate it; and the rooms where stores of fruit are kept, are known to be very unwholesome, and persons have been suffocated by sleeping in a room where there was a very great quantity of flowers. ”

“ Carbonic acid, one of the most common and stable compounds in the world, the final resultant of all combustion, loses its oxygen under excessive heat, and becomes an oxidizing agent. In this way good authorities explain the production of phenic, acetic, and cresylic acids, as hydrocarbons oxidized by the oxygen of carbonic acid. The hydrocarbons may also be dissociated. A liquid hydrocarbon analogous to benzine, toluene, takes hydrogen and leaves a deposit of anthracene. ”

“ Blackness, you know, does not appear to be essential to carbon, and it is pure carbon, and not charcoal, that we must consider 292 as the basis of carbonic acid. We shall make some carbonic acid, and, in order to hasten the process, we shall burn the carbon in oxygen gas. ”

“ We are assured by the best chemists, however, that the average quantity of carbonic acid generated by a person in health in twenty-four hours is about 40,000 cubic inches, and this contains only about 111⁄2 ounces of pure carbon. Rather less than half an ounce is therefore used per hour in preserving the body at its usual temperature. ”

“ From whatever source, however, the carbonic acid may arise, it is not the less prone to mingle with the surrounding air, and where the level of the floor of the church is below the level of the churchyard, there the carbonic acid is prone to accumulate, as, though it may be ultimately dispersed by diffusion, it may be considered as flowing in the same manner in the first instance as water, where the quantity is considerable. ”

“ But this power lasts no longer than the effervescence. The mineral acids react upon the chromate of potash only when vegetable colouring matter, gum, starch, or a vegetable acid are present, to determine the disengagement of gas. During this curious change carbonic acid is evolved; and when it takes place in a retort, there is condensed in the receiver a colourless liquid, slightly acid, exhaling somewhat of the smell of vinegar, and containing a little empyreumatic oil. This liquid heated with the nitrates of mercury or silver reduces these metals. ”

“ It has been calculated that if this carbonic acid had been at one and the same time in our atmosphere it would have caused an elastic pressure fifty times that of our present atmosphere; and if we add the carbonic acid that must have been absorbed in vegetation in order to form our coal-beds we should probably have to double that pressure. Animal life, of which we had abundant traces in these 'measures,' could not have existed under such conditions, we are almost forced to the conclusion that the carbonic acid must have been derived from an external source. ”

“ Waters of this class owe their properties chiefly to Carbonic Acid. They sparkle when drawn from the spring, or when poured into a glass; have an acidulous taste, and become vapid when exposed to the air. Besides free carbonic acid, on the presence of which these qualities depend, acidulous waters contain generally carbonates of Soda, of Lime, of Magnesia, and of Iron ”

“ Carbonic Acid.—This, the most important compound of carbon and oxygen, is best obtained by pouring a strong acid upon chalk or limestone, when it escapes with effervescence. It is a colourless gas, extinguishing flame, incapable of supporting respiration, much heavier than atmospheric air, and slightly soluble in water, which takes up its own volume of the gas. It is produced abundantly when vegetable matters are burnt, as also during respiration, fermentation, and many other processes. ”

“ If carbon alone be employed, carbonic acid gas is the result; if oil, tallow, rosin, or turpentine be used, we have then, as we had occasion to remark, [4] water, as well as carbonic acid, by reason of the union of the hydrogen, which forms one of their constituent parts, with a part of the oxygen of the nitric acid. ”

“ 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. ”

“ The result depends upon the fact, that little or no carbonic-acid gas is expelled from the liquid on the addition of the test-acid, until the caustic portion is very nearly neutralised.
The quantity of WATER or MOISTURE, per cent., present in an alkaline carbonate, is indicated by the loss of weight which 100 gr. suffer on gentle ignition in a loosely-covered iron dish or platinum crucible. ”

“ Carbonic acid is found most largely in solid combinations with other bodies: it forms 44-100ths of all limestones and marbles, and it exists in smaller quantity, combined with other earths, and with metallic oxides. ”

“ Water is the most neutral of bodies: usually producing little chemical alteration in the substances with which it combines; and being expelled from most of its combinations by a moderate heat. Carbonic acid is a relatively feeble acid: the carbonates being decomposed by the majority of other acids and by ignition. The various hydro-carbons are but narrow in the range of their comparatively weak affinities. The compounds formed by ammonia have not much stability: they are readily destroyed by heat, and by the other alkalies. ”

“ Carbonic oxide is neither acid nor basic, but carbonic acid is an acid oxide, and as such unites with oxides of the basic class to form another range of compounds. Thus, for example, the oxide of the metal calcium is quicklime, which is strongly basic, and this directly combines with carbonic acid, forming a neutral substance called in systematic chemistry calcium carbonate, or more commonly but less correctly, carbonate of lime, familiar to everyone in the compact state as limestone, and marble, and in a more or less pulverent condition as chalk. ”

“ Quite so, uncle. Burn carbon or charcoal either in the air or in oxygen, and it is sure always to make carbonic acid, and nothing [pg 297] else, if it is dry. No dew or mist gathers in a cold glass jar if you burn dry charcoal in it. The charcoal goes entirely into carbonic acid gas, and leaves nothing behind but ashes, which are only earthy stuff that was in the charcoal, but not part of the charcoal itself. And now, shall I tell you something about carbon? ”