Limekiln

“ The chemical composition of the original limestone also has an influence on the character of the burnt lime. Limestone consisting entirely of carbon dioxide and lime is so rare that sufficient is never available for making burnt lime on a large scale. Even the purest limestone found native in large quantities—namely marble—is not pure carbonate of lime, but contains a certain proportion of extraneous substances. At the same time it is too expensive to use for technical purposes.
The ordinary impurities present in limestone are91 ferrous oxide, ferric oxide, magnesia and organic matter. ”

“ Limestones, however, are metamorphosed by pressure into marble, the grains of carbonate of lime recrystallizing freely to interlocking crystals of calcite.
These few examples must suffice of the great class of metamorphic rocks. As we have seen, they owe their origin to the alteration of both of the other classes of rocks—the sedimentary and the igneous—by heat and pressure, assisted usually by the presence of water. The fact of change is seen in their hardness arid cementation, their more or less complete recrystallization, and their foliation ”

“ It may also be presumed that a blue water, containing limestone in full solution, should become green when lime is added to it. This is illustrated on the north shore of the Lake of Achen, where the blue waters of the deep lake become chrome-green when they break over the limestone pebbles of the strand, and, generally, in the greener color of the bottom and shore waters of seas and lakes. Other substances than lime, particularly silica and alumina, may produce the same effects, but their action is more complicated. ”

“ Combined with carbonic acid (26) it forms limestone (140) , chalk, and marble; all of which are capable of being converted into lime by burning. Lime may also be obtained from oyster and other sea shells. When pure, it is of white colour, and moderately hard substance, though it is easily reducible to powder. Its taste is burning and acrid; and, like the alkalies, it changes vegetable blue colours to green. It has likewise the property of corroding and destroying animal substances. Lime, when pure, absorbs water rapidly, becomes hot, and falls into powder. ”

“ There the amount of evaporation is often sufficient to cause a re-deposit of the mineral in solution. If it be lime, a white crust gathers along the sides of the stream, delicately enveloping grass-stalks, leaves, twigs, snail-shells, and other objects, which it may meet with in its progress. Such "petrifying" springs, as they are popularly termed, occur abundantly in our limestone districts. It should be borne in mind, however, that they only produce an incrustation round the organic nucleus, and do not petrify it. ”

“ The cliff was not 100 yards long, and was about 70 thick; its surface was shivered by frost into cubical masses, and glacial boulders of gneiss lay on the top. The limestone rock was chiefly a blue pisolite conglomerate, with veins and crystals of white carbonate of lime, seams of shale, and iron pyrites. A part was compact and blue, very crystalline, and full of encrinitic fossils, and probably nummulites, but all were too much altered for determination.
This, from its mineral characters, appears to be the same limestone formation which occurs throughout the Himalaya and Western Tibet ”

“ Limestones weather much more rapidly than clay-rocks; and augitic igneous rocks, as a rule, disintegrate more readily than the more highly silicated species. The weathering action of the atmosphere is also greatly aided by frost, as we shall see presently. The result of all this weathering is the formation of soil—soil being only the fine-grained débris of the weathered rocks. The angular débris found at the base of all cliffs in temperate and arctic regions, and on every hill and mountain which is subjected to alternations of extreme heat and cold, is also the effect of weathering. ”

“ The lime causes the minute separate particles of clay to flocculate or group themselves together into larger compound grains between which air and water can percolate more freely. It is this power of creating a more crumbly tilth on stiff clays that makes lime so valuable to the farmer. Lime also assists in the decomposition of the organic matter or humus in the soil and promotes nitrification; hence it is of great value after green manuring or where the land contains much humus from the addition of bulky manures such as farm-yard dung. ”

“ It has already been stated that the Carboniferous or Mountain Limestone underlies the coal-measures in the South of England and Wales, whereas in the North, and in Scotland, marine calcareous rocks partly of the age of the Mountain Limestone alternate with shales and sandstones, containing seams of coal. In its most calcareous form the Mountain Limestone is destitute of land-plants, and is loaded with marine remains—the greater part, indeed, of the rock being made up bodily of crinoids, corals, and bryozoa with interspersed mollusca. ”

“ The particular form in which lime should be applied for the best results depends upon the nature of the soil. In practice the proximity to chalk pits or lime kilns, the cost of the lime and cartage, will determine which is most economical. Generally speaking light poor lands deficient in organic matter will need the less caustic form or chalk, while quicklime will be most satisfactory on the stiff clays and richer soils. On the stiff soils overlying the chalk it was formerly the custom to dig pits through the soil to the rock below. ”

“ If this is not the case, the burnt lime is greyish in colour, from the finely divided particles of carbon, which, of course, spoils the lime for colour-making. The defects existing in lime burned in the above type of kiln originate in the irregular character of the product. It will be evident that the limestone lumps that are nearest the fire will be far more strongly heated than those in the upper part of the dome; and when calcined lime is kept incandescent for a long time, it becomes so compact in texture that it quenches with great difficulty when brought in contact with water. ”

“ A country of rolling downs extends on every side, framed by the distant landmarks just described. Yet the prevailing hue is not that of grass, even at this season; but of naked limestone, weathered a pale ochre, or of serpentine, dull-green or bluish-grey. Both rocks compose hills of a gently rounded character; the limestones are most often capped by slabby lavas, which resist the crumbling and contribute to the horizontal appearance of all higher forms. The few clouds which have scaled the barrier of the Palandöken send liquid shadows over the undulating expanse. ”

“ Now, in later formations, limestone is usually an organic rock, accumulated by the slow gathering from the sea-water, or its plants, of calcareous matter, by corals, foraminifera, or shell-fish, and the deposition of their skeletons, either entire or in fragments, in the sea-bottom. The most friable chalk and the most crystalline limestones have alike been formed in this way. We know of no reason why it should be different in the Laurentian period. ”

“ It may therefore be considered as a discovery of some importance, that we possess, in this country, a species of limestone which, when used for purposes of extracting lime, and in the preparation of mortar, is capable of communicating to the cement all the properties of the pulvis Puteolanus. ”

“ Among more consolidated limestones, as we have hinted, the joints are effective in promoting bold rock-scenery. The absorptive power of the rock, rather than its hardness, prevents it from being washed away. Water that might round the edges of escarpments and send down taluses to modify the slopes sinks into the ground and works out passages by solution. On level surfaces, the solubility of limestone in water charged with carbon dioxide from the atmosphere is apparent by the formation of pitted hollows, with edges between them that grow sharper until they are worn through. ”

“ Gas lime is also frequently used as manure; in gas works, quicklime is used for removing the impurities from the gas. Gas lime, therefore, varies considerably in composition, and consists really of a mixture of slaked lime, or calcium hydrate, and carbonate of lime, together with sulfites and sulfides of lime. These last are injurious to young plant life, and gas lime should be applied long before the crop is planted, or at least exposed to the air some time before its application. The action of air converts the poisonous substances in it into non-injurious products. ”

“ Formerly the Limagne, that vast expanse of sandy and argillaceous soil, of which you can scarcely see the limits, was on a level with the first table-land of the mountains; but owing to the geological character of its lower portions, it subsided, so as to tear away the edge of the mountain, as I explained to you a moment ago. Now this immense sinking produced, at the point of separating the earth and the granite, an immense barrier of clay of great depth and impenetrable by liquids. And this is what happens: The mineral water comes from the beds of old volcanoes. ”

“ Much of the lime on the market in the Philippines has been made without any attempt to select pure clean limestone or shells. This is not suitable for putting into cane juice, and will result in a great deal of trouble whenever used in modern evaporating plants. There is, however, an abundant supply of limestone found in various parts of the Philippines, which analyses show to be almost free from impurities, and which will make a most excellent lime for clarifying purposes if burned properly. ”

“ Their remains, buried in the earth, would increase the quantity of carbonate of lime in a form available for the use of animals and plants; that is, lime would gradually be eliminated, by plants and animals, from its more concealed combinations in the crystalline rocks, and be converted into carbonates, sulphates, and humates. A larger amount of organic matter would also be converted into humus. Now, limestone soils are of all others most favorable to vegetation, when there is a sufficient supply of organic matter. ”

“ The stone contained its lime in carbonate form, and when reduced to good physical condition for distribution it helped to make highly productive land. We know that lime carbonate does the needed work in the soil so far as correction of acidity is concerned, but in the form of blocks of limestone it has no particular value to the land. Burning and slaking afforded to man a natural means of putting it into form for distribution, and it is only within recent years that the pulverization of limestone for land has become a business of considerable magnitude. ”

“ Limestone rock, on the other hand, is commonly laid down in horizontal strata, and while a succession of strata may frequently give rapid slopes, marshes are very common, existing even on the tops of the hills. The drinking water is always to be suspected as to quality because, in the first place, it is hard from absorption of lime, and in the next place, cavities and seams in the rock allow polluting material to travel for long distances. ”

“ The day would come when the surface soil could not produce our staple crops if its loss of lime continued, and a means of replenishing the stock were not at hand. The huge deposits of limestone that have not been disintegrated by processes of weathering are assurance that the soil's need can be met forever. The calcium and magnesium in the stone are in chemical combination with carbonic acid forming carbonates, and there is an additional mixture of other earthy material that was deposited by the water when the stone was being formed, but much limestone possesses an excellent degree of purity. ”

“ Pure limestone is white, but if it contains clay or plant or animal matter it is light gray, dark gray, or black. Limestone also may be some shade of yellow, brown, or red. It is fairly soft and can be scratched with a knife. Because this rock contains calcite, an easy chemical test will help identify it: a drop or two of dilute hydrochloric acid will quickly fizz and bubble when placed on the limestone.
Limestones form in fresh water, such as in lakes, but most of them form in the seas. As some earlier-formed rocks are weathered, the calcium minerals that they contain are dissolved. ”

“ Old heaps will remain in hydrate form for many years, excepting the outside coat, which excludes the air. Complete air-slaking would not reduce ability to correct soil acidity, the total amount of calcium and magnesium remaining constant, but weight would be added in the slaking, and therefore the value per ton would be reduced. The slowness with which air-slaking proceeds gives reason to expect that any bulk of old lime may contain a considerable percentage of the hydrate, and therefore have greater strength than a true carbonate like limestone. ”

“ Such deposits are formed simply by the precipitation of carbonate of lime from water, in consequence of the evaporation from the water of the carbonic acid gas which formerly held the lime in solution; but, though sometimes forming masses of considerable thickness and of geological importance, they do not concern us here. Almost all the limestones which occur in the series of the stratified rocks are, primarily at any rate, of organic origin, and have been, directly or indirectly, produced by the action of certain lime-making animals or plants, or both combined. ”