In a communication to the Board of Agriculture, Mr. Rawson described a method of constructing a lime-kiln, by which a considerable saving of fuel was effected.
This kiln was made 20 feet in height ; at the bottom was placed a metal plate, one foot in height, intended to give air to the fire ; the sloped sides were 6 feet in height, the breadth at the top of the slope 8 feet ; the sides carried up perpendi cular 14 feet ; so that every part of the inside, from 14 feet to the mouth, was exactly of the same dimensions. On the mouth of the kiln was placed a cap, built of long stones, and rather sharply contracted, about 7 or S feet high. In the building of this cap, on one side of the slope, the mason be ing over the centre of the kiln, anything dropping down would fill perpendicularly to the eye beneath. Here was placed an iron door 18 inches square, and then the remainder of the building of the cap was carried up until the whole of the top was contracted to 14 inches. The kiln was fed throngh the iron door, and, when filled, the door was close shut. The outside wall was 3 feet at the bottom battering up to 2 feet at top, and built at such a distance from the inside wall of the kiln, that 2 feet of yellow clay might be well packed in between the walls; without this precaution kilns are almost certain to split. At S feet high from the eye of the kiln, two flues were carried through the front wall, through the packed clay to the opposite side of the kiln, to give power to the fire. It is asserted, that, with this kiln, one-third more lime has been produced from a given quan tity of fuel, and also that stones of bad quality might be put into the kiln without the necessity of being broken so small as usual. As many situations will not admit of building a kiln 20 feet high. while other situations may allow of its being built 30, or even 40 feet, (fur it cannot be made too high,) the diameter of the kiln should be proportioned to the height to it is carrieil up.
In the same communication, Mr. Rawson also described another and rather curious application of this sort of contri vance. lie states that, " for several years, he has made use of a small kiln in an outside kitchen, the height 9 feet, the diameter 31- feet. In the side of the kiln next the fire, he had 3 square boilers placed, one of them large, half a barrel, with a cock, which supplied the fitfully with constant boiling water ; for the two others, he had tin ves sels made to fit the inside with close covers, in which meat and vegetables with water were placed, and put into the two smaller boilers, which never had any water, but had close covers. The tin boilers were heated sooner than on the strongest fire, and when the meat, &c., were sufficiently dressed, the whole was taken out of the metal boilers. At one side he had an oven placed for roasting and boiling meat ; the bottom was metal of 26 inches diameter, and 1 inch thick, it flue from the fire went underneath. Even with the bottom of the oven, a grating 9 inches square was placed, which opened a communication between the oven and the hut fire of the kiln. The height of the oven was 14 inches, shut close by a metal door of 18 inches square, and the top, level with the mouth of the kiln, was covered by another metal plate of half an inch thick, on which was placed a second oven ; the heat which escaped through the half-inch plate, though not near the tire, was sufficient to do all small puddings, pies, breakfast-cakes. &c. &c. The meat in the
large oven was placed on an iron frame, which turned on a pivot, and stood on a dripping-pan, and was turned by the cook every half hour. And over the kiln he had a tiled stage for drying corn, and a chimney at one side, with a caul on the top, which carried off all steam and sulphur : a large granary was attached to the building." It is added, that the lime. if sold, would more than pay flu- fuel and attendance; and he has frequently had dinner dressed for fifty men, with out interfering with his family business in any great degree.
An admirable combination of a lime-kiln, with a coke-oven, was the subject of a patent granted to Mr. Charles Ileathorn some years ago, since \ hich time it has been in successful operation at Maidstone and other places. The object of this invention, as expressed in the specification of the patent, is the preparation of quick-lime and coke in the same kiln at one operation. The economy of this process must be evi dent from the circumstance, that the inflammable part of the coal, which is separated to form it into coke. is the only fuel employed to burn the lime ; and as the coke is in many places as valuable as the coal from which it is prepared, the cost, if any, of making lime, must be reduced to the most trifling amount.
In burning lime, some burners prefer peat to coal for the fuel ; but that preference has probably arisen from an inju dicious management of coal. Mr. Dobson asserts peat to be more economical than coal ; that coal, by its excessive heat, causes the limestone to run into solid lumps, which it never does with peat, as it keeps them in an open state, and admits the air freely ; -that the process of burning goes on more slowly with coal, and does not produce half the quantity of lime.
This inconsistency requires no comment ; nevertheless, peat is a very useful fuel for the purpose, and an excellent substitute for coal, where the latter is scarcer or dearer. All kinds of lime exposed to the air recover nearly their original weight, except chalk-lime, which, altlumgh long exposed, never recovers more than seven-eighths of its original weight. Seine limestones, as Po•tland-stone, yield a very white lime ; others, as chalk and roe-stone, a lime with a yellowish cast ; the latter is best adapted for mixing with tarras, puzzolana, or Parker's cement, for buildings under water. It has long been said by lime-burners, that if lime stone be-imperfectly burned in the first instance, no further exposure of it to the fire will produce quick-lime. This assertion, which it was supposed was the offspring of igno rance, has been confirmed by M. Vicat, in a valuable treatise lately published by him on mortar and cements. Such lime, which is technically termed dead lime, does not slake with water, but upon being ground and made into a paste with water, differs from common mortar by setting under water.