Limestone

T h e B a l d w i n P r o j e c t

The Wonder Book of Chemistry by Jean Henri Fabre

There is carbon, I say, in chalk; but it is in the burnt state, and to burn it over again is impossible unless its present partnership with oxygen is first dissolved. Consequently, chalk is incombustible. But carbon abounds in numerous other substances, and in an unburnt condition; therefore it is combustible.

Once more: The black smoke of the burning paper and the black color of its charred fragments make us pretty sure, without the help of lime-water, that paper contains carbon, just as the black smoke rising from a smoldering candle-wick makes us think the candle has carbon in it; and this we infer despite the whiteness of both paper and candle. But now we come to a third substance that gives no similar indication of the presence of carbon. It is alcohol, or spirit of wine.

As soon as the alcohol stops burning I apply the lime-water test. The water is whitened. That settles it. I can now affirm with absolute certainty that alcohol, a liquid as colorless and transparent as water, contains that compact black, opaque substance called carbon.

Chalk, marble, and all limestones contain carbonic acid, an acid of little strength and always ready to give up its place to any other acid that is more powerful. In chemistry the harsh law of the strongest prevails: get out of that and make room for me. If, then, we pour some strong acid on carbonate of lime, carbonic acid is set free, being ousted by the new-comer, which takes its places and forms with the lime a new salt. Sulphuric acid, for example, turns a carbonate into a sulphate, and phosphoric acid turns it into a phosphate. In both cases the carbonic acid is set free, and its release is accompanied by a foaming on the surface of the stone.

The word 'limestone' means carbonate of lime; but there are many other carbonates, each metal giving one of its own, or sometimes more than one, as occasionally there are several carbonates for the same metal. Iron, copper, lead, zinc, to name no others, have each its own carbonate, just as calcium has, this last being, of course, carbonate of lime, or limestone. This carbonate is much more plentiful than any of the others, and plays a more important part in this world of ours; therefore I particularly call your attention to it. A good half of the soil is made of it. Great mountain-chains are blocks of this salt. Whether rare or abundant, all carbonates without exception have the peculiarity of effervescing when touched with an acid.

Here, then, is our carbonic-acid gas. It is as colorless, as transparent, as invisible as air. We have just extracted it from limestone, where chemical combination held great quantities of it captive with a very narrow compass. A piece of stone hardly bigger than a walnut will yield several liters of it. We have just driven some of it our of the rock, and are now going to drive it back and make it reenter the composition of rock,—that is to say limestone, powdered chalk. I pour some lime-water into the bottle that is filled with carbonic-acid gas, close it tightly with the palm of my hand, and shake it thoroughly. The liquid turns white and thick like sour milk. We let it stand a while, and flakes settle at the bottom in a considerable layer. You know these white flakes as carbonate of lime, chalk, the compound we obtained when we shook up lime-water and carbonic acid obtained by burning charcoal. So here we have fresh proof, to add to the others, that limestone really contains the gas produced by burning charcoal.

The gas has disappeared, being shut up once more in the stone,—or, rather, in a sort of mud that would become stone if it were dried and pressed.
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Berthollet, Claude Louis (1748-1822)
French chemist who carried out research into dyes and bleaches (introducing the use of chlorine as a bleach) and determined the composition of ammonia. Modern chemical nomenclature is based on a system worked out by Berthollet and Antoine Lavoisier.

Berthollet was born in the then Italian region of Savoy. He qualified as a physician at the University of Turin, moving to Paris to study chemistry. As private physician in the household of the duke of Orléans, he carried out research in the laboratory at the Palais Royale. He was appointed inspector of dyeworks and director of the Gobelins tapestry factory 1784. He taught chemistry to Napoleon and went with him to Egypt 1798. There he observed the high concentration of sodium carbonate (soda) by Lake Natron on the edge of the desert. He reasoned that, under the prevailing physical conditions, sodium chloride in the upper layer of soil had reacted with calcium carbonate from nearby limestone hills - the beginning of his theory that chemical affinities are affected by physical conditions, in this case the heat and high concentration of calcium carbonate. In 1804 he became a senator but ten years later voted for the deposition of Napoleon.
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