600 COTTAGE, FARM, AND VILLA ARCHITECTURE. Design VI. — An improved Limekiln. 1281. Limestone is burnt in a variety of ways. The object is, completely to deprive the stone of its carbonic acid gas with the smallest quantity of fuel, the least amount of labour, and in the shortest time. The rudest mode of burning lime is by mixing the stones with coal or other fuel, in large open heaps, and then setting fire to the coal or fuel. The first improvement on this mode consisted in covering up the heap with earth or turf, so as to confine the heat; a practice which, we are informed, is still followed in the islands of the West Indies. The nest improvement was the forming of a well for burn- ing the lime in the face of a bank, so that the stones and fuel could be thrown in at top, and drawn out, as burnt, at bottom. The ordinary form employed for this purpose is that of an inverted cone, or an egg with the broad end uppermost. The first improve- ment on this form was made by Booker of Dublin. The section of Booker's kiln forms two long narrow truncated cones, placed end to end, giving a width, or diameter, at the base and apex of three feet, and in the middle of seven feet. A suitable height for these dimensions is from twenty-five to thirty feet. On the top is a cast-iron cap or cover, which turns on a pivot, and rests on a curlj-ring fixed on the top of the masonry of the kiln. The use of this cover is to prevent the escape of more heat than is necessary to keep the fuel burning, and, therefore, the opening at the top of the cap is a circle of not more than twelve inclies in diameter. Very little heat is thus lost, and lime may be burned with as little fuel in winter as in summer. Another great advantage of this plan is, that by closing the orifice at the top of the cap and the furnace-doors below, the fire may be kept alive for four or five days, which, in situations where the demand for lime is not regular, is an object of some importance. Booker's limekiln has subsequently been materially improved by C. J. Stuart Menteath, Esq., the proprietor of extensive lime- works at Closeburn, in Dumfries-shire ; and it is this kUn which constitutes our present Design. Booker's, and a vai-iety of others, will be found described in our Encyc. of Agr., 2d edit. § 3862. 1282. The Closeburn Limekiln is oval in the plan at top, and perpendicular in the sides to nearly half its depth ; below which it is gradually contracted to the size of the grating of the furnace. The advantage of the oval form is, that the combustion is more regularly sup- plied with ail- than in the case of a kiln of large diameter. " Narrow kilns," Mr. Men- teath finds, " also burn much faster, admit of there being drawn out of them every day {if fiilly employed) more than two thirds, or nearly three fourths, of what they contain of well-burnt line ; and afford fully three measures of calcined lime for one measure of coal, when large circular kilns will not give out one half of their contents every day, and require nearly one measure of coal for two measures of lime burnt." In a country sale of lime, Mr. Menteath remarks, " the quantity sold every day is liable to great fluctuations: two or three cart-loads will sometimes only be required from an establish- ment which the day before supplied forty ; and, as lime is known to be a commodity which, when exposed to the action of the air, becomes more bulky and heay, and in that state does not admit of being carried to a distance without additional labour, it has been an object of importance with me, to find out a construction of a kiln which will allow of lime being kept for several days without slaking, and, at the same time, to prevent the fire escaping at the top of the kdn, if the kiln stands twenty-four hours without being employed, especially during the autumn and winter, when the air is cold, and the nights long. I now employ kilns of an cgg-sha))e, and also oval. The oval-shaped kilns are divided by arches across the kiln, descending foiu- feet from the top. The object of the arches across the kilns is to prevent the sides of the kUns from falling in or contracting, and also for the purpose of forming cu'cular openings for feeding in the stone and coal at the mouth of the kiln. Upon this plan, a kiln of any length might be constructed with numerous round mouths." Having placed a lid to the cover of Booker's iron cap, Mr. Menteath is enabled " to prevent the escape of heat at the top, and by cast-iron doors at the bottom the air is prevented from passing through the kiln ; so that by these pre- cautions the limel)urner can regulate the heat, and prevent its escape for several days ; when without them the fire, in winter, would be extinguished in the course of twenty-four hours. This is an object of great importance, as it enables one to burn lime as well, and with as small a quantity of fuel, in the winter as in the summer season ; and to sup- ply tlie farmer with well-burned lime at any time of the year : an object which cannot be obtained by the common construction of kilns, open both at top and bottom, for the reasons before stated." 1283. Burning Lime with Coke instead of Coal. " From the great expense attending the carting of fuel from a distance of twenty-five miles from my own coal-pits, I have adopted the practice of coking the coal, which is a saving of ciglit twentieths of the weight ; and I find that equal measures of coal and coke give the same quantity of heat in burning lime, which appears paradoxical, but is not the less true. The coal
