LIME and LIME KILNS EUGENE W. BLANK Colgate-Palmolive-PeetCompany, Jersey City, New
Jersey
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NDOUBTEDLY one of the first chemical discoveries of ancient man was lime. Once man had progressed to the point of using fire and building fireplaces the discovery was impendent, for i t was inevitable that eventually he would unwittingly employ limestone in the construction of his hearth, with the resultant production of lime. Many years must have passed, however, before he learned to utilize the valuable oro~ertiesof lime in the arts and crafts of his time. If limestone is heated to dull redness (approximately 550°C.) it begins to decompose, liberating carbon dioxide and leaving a residue of calcium oxide or quicklime as it is more generally known. In a closed container the decomposition stops when the pressure of the carbon dioxide reaches a point known as the dissociation pressure. This dissociation pressure has a definite value a t each temperature and under such conditions the system is in equilibrium. Wben the reaction is carried out in an open vessel so that the carbon dioxide can readily escape, the reaction goes practically to completion. If steam is passed through the vessel, decomposition occurs still more readily. The process of heating limestone to procure quicklime is known as lime burning and the open vessels employed for lime burning are called kilns. The literature on the subject of lime burning is immense. Spackman (1) alone mentions approximately two hundred ninety authoritative writers on lime and cement from the earliest to the present period. Generally speaking, lime burning did ,not properly constitute an industrial process until about q e middle of the past century. Prior to that period lime burning was carried on t o supply the lime burner's own immediate needs and purely local requirements, and even today some lime is being produced under such a status. Probably the paramount reason lime, for so many years, was utilized in close proximity to the kiln in which it was produced was due to the difficulty and danger of storing and transporting it. The advent of barrels, and particularly the steel drnm, together with the development of the modem continuous kiln spelled the epilogue of what was once a flourishing chemical operation carried on in thousands of localities. In many sections of this country there was a homemade rock "pot" kiln on almost every farm of any size, but today the great majority of these kilns have been abandoned and are rapidly disintegrating and disappearing. Cato (B.c. 234-149) is the first writer mentioned by Spackman (2). Cato, after he had attained fame and fortune by serving the Roman state in both civil and military life, continued to maintain his interest in agriculture. His De Re Rustica is essentially a treatise
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on farming, but it contains a few paragraphs on lime burning. The shape and dimensions of lime kilns are given and also the precautions to be observed in burning limestone to obtain a good quality product. Cato gives the dimensions of a kiln as ten feet wide and twenty feet deep, tapering to three feet wide a t the top of the furnace (3). Cato proceeds to give instructions regarding the proper operation of the kiln and points out that continual watch is necessary to prevent the fire in the kiln from consuming itself. As white a stone as possible should be put in the kiln, and the burning is complete when a less smoky flame comes out of the top of t h e kiln. Vitruvius, a celebrated Roman engineer and architect. lived durinp the reien of Aueustus (B.c. 27-A.D. 14): In Book I1 of his famous De LchitectAra, Chapter ~ i v treats e of lime. Vitrnvius stresses the point t h k a white stone should be used in the production of lime (4), " with regard to lime we must be careful that it is burned from a stone, which, whether soft or hard,
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is in any case white. Lime made of close-grained stone of the harder sort will be good in structural parts; lime of porous stone, in stucco . . . " Vitrnvius goes on to explain why lime becomes solid when mixed with water and sand and finally makes the significant observation (5) that " . . . limestone when taken out of the kiln cannot be as heavy as when it was thrown in, but on being weighed, though its bulk remains the same as before, it is found to have lost about a third of its weight' owing to the boiling out of the water."
Attention was early directed to the baffling (and dangerous) chemical proclivities of lime. I n this connection Pliny (A.D. 23-79) wrote (6),"We cannot fail to marvel that a material which has been already burned, is again inflamed by water." The chemical knowledge of the Greeks and Romans was not sufficiently advanced to explain the phenomenon of slaking, but they utilized lime widely in the constmction of buildings. Pliny complains of the collapse of many such structures and bluntly points out the cause, "The chief causes of the collapse of so many buildings in
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1 The theoretical loss of pure calcium carbonate would he 43.96 per cent.
Rome is the pilfering of lime, as a result of which stone is laid on stone without proper mortar. The older the slurry is, the better. The building laws of our ancestors contained a provision that contractors should use no mortar less than three years old, which explains why their stucco has never spoiled by cracking." Pliny has little to say concerning the burning of lime and in general his observations on lime are largely a recapitulation of what Vitruvius and others had previously written on the subject. We have seen that Vitmvius considered the properties of lime to be eneendered by the loss of water during the burning operati&. As a matter of fact the chemical change which occurs during the conversion of limestone into caustic lime was not really understood until J. Black in 1777 a t Edinburgh published his celebrated thesis, "Experiments upon Magnesia Alba, Quicklime, and other alcaline substances." Lime burning became a quite common operation in and around London during the Middle Ages when stone buildings were being erected in increasingly large numbers. The vendors of lime tended to congregate in one section of the city and Sea Coal Lane, near Ludgate Circus, was often referred to as "Limeburners Lane" for a great part of the colliers' business was with those who required fuel for kilns (7). From about 1200 to 1300 the use of coal was restricted in general to ironworking and lime burning, because the absence of chimneys rendered i t unsuitable for use as a household fuel. Whenever sizable building operations were nndertaken, and correspondingly large quantities of lime were required, it was customary to build lime kilns adjacent to the building site. These kilns were usually small and temporary structures. Where lime was burnt for sale and not for use on the spot, the kilns were usually of larger capacity and more substantially constructed. A sixteenth-century account of the erection of eight such kilns a t an unspecified localitv-orobablv Calais-records that each kiln was , twenty feet high, with walls ten feet thick, and an averace internal breadth of ten feet, and cost over 450s 78). Lime was burnt in this country a t Providence, Rhode Island, as early as 1661 and camed into Boston. In 1723 a lime kiln was put into operation near the Bowling Green in Boston. Previously, in 1697, considerable excitement had been occasioned by the discovery of limestone in Newbury, Massachusetts (9). In outlying sections, early in the history of our country, it was usual for each farm to have its own kiln, which was in most cases a solid stone structure built against a hill so that it could be readily filled from the top with limestone. Such an arrangement also materially strengthened the kiln and helped to insulate and conserve the heat during the lime burning. In general pot kilns were about twenty feet deep, about six feet in diameter a t the top widening to a diameter of about seven feet and then contracting to about two feet by a foot and one-half at the bottom where there
was an opening in the side about eighteen inches square known as the "eye" or "draw-hole" (10). The kilns were usually lined with a lire-resistant stone found in the vicinity. Usually no grate was used, the kiln being filled with alternate layers of stone and wood. A quantity of brushwood interspersed with the lower layers permitted ignition of the fuel used in the kiln. If the kiln was provided with a grate a layer of wood
still be observed south of Frogtown in Clarion County agd close to Ford City in Armstrong County, both in Pennsylvania (11). Although, as already indicated, lime has been burned in thousands of places in this country, certain localities have been especially favored by the quantity, and particularly the quality, of limestone available and their strategic location as shipping centers.
F~oune3.-A PLATE ow PARTICULAR INTEREST AS SHOWINGTHE GREAT VARIETYOP SHAPES A SIMPLE POTKnN CANHAVE.TAKEN FROX THE "NOUVEAU MANUEL DU CHAUWURNIER" BY BISTON(14 wm laid on the grate. Over this was erected an arch of large stones, considerable space being left between the stones. This arch supported the balance .of the stone with which the kiln was subsequently filled. The stone was packed sufficientlyloosely to permit a good draft. The wood was ignited and as it was consumed was replenished from time t o time. No very reliable method for determining when the limestone was completely burnt existed. The shrinkage of the contents of the kiln provided some indication to an experienced lime burner. Another indication was the ease with which an iron bar could be inserted into the kiln, as limestone upon burning become? relatively softer, but this method failed in case the stone burned to a hard, dense lime. Most operators were colitent to allow the kiln to burn for a period of about seventy-two hours, trusting to luck that in this length of time the stone would be completely converted into lime. These kilns were exceedingly wasteful of fuel, since the kiln was allowed to cool down each time a batch of lime was produced. Production also was quite limited. Through the course of many years lime kilns have taken every conceivable shape, usually with the object of improving the quality or quantity of lime produced from a given weight of fuel. As a result of this empirical testing i t has been found that, generally speaking, the shape of a simple pot kiln is of secondary importance. Another method utilized in burning lime was the open pile method. In some districts in Pennsylvania the burning is still done in this fashion by stacking alternate layers of wood or soft coal and blocks of limestone so arranged as to cause a good draft through the pile. After the fuel is well ignited earth is thrown over the pile. It is reported that open heap burning can
Lime was produced in Maine very early, probably about 1733. "Samuel Waldo, of Boston, having by purchase or inheritance from his father, obtained a title in the lands of the St. George and Medomac rivers: having made experiments upon the limestone found near the river a t what is now called the prison quarry, and finding it good, he caused a new lime kiln to be erected, and lime burnt in considerable quantities for ' the Boston markets" (12). .. By 1835 th; annual production in the state had increased to nearly three-quarters of a million casks. Rockland, >l&nc,soon took the lead as a lime center. In this locale the limestone was formerly b r o u ~ h tby ox or horse team to kilns located conveniently close to the harbor. From Rockland harbor lime was shipped by schooner to aU points. The parallel activity of bringing in wood to feed the kilns engaged more sailing vessels than the actual shipping of the lime itself. A peculiar style of short stumpy boat known as "Saint John Woodboats" gradually evolved. -These vessels were closereefed to permit raising the booms above high deck loads, and from the wide, flat stern devoid of any semblance of overhang usually hung a yawl boat. Many of these wood boats had no bowsprits. These vessels were quite often tremendously overloadedand burdened with enormous deckloads, but losses by sinking were generally rare due to the buoyancy of the cargo, although vessels not infrequently sailed slowly into port with the helmsman standing kneedeep in water (13). On the other hand, exporting lime from Rockland required staunch and dry vessels due t o the dangerous nature of the cargo. Many of these lime schooners became world famous and are still remembered by name to this day. '
Occasionally a vessel sprang a leak and the heat of the lime reacting with the water started a fire. Smothwing the conflagration was the only salvation. A cask of lime was speedily broached, its contents made into a thick paste with water and all the crevices and cracks in the deck and around the hatches were plastered shut. The vessel was then turned toward the nearest port while the crew labored and waited in suspense, sometimes the fire was readily smothered; then again the vessel oftenlay upu in harbor for months before the fire died out or i t was decided to scuttle the ship. Sinking the vessel was sure to extinguish the
fire but the swelling lime casks usually burst the vessel's sides with total loss of the boat so that scuttling was resorted to only as a kill.or.cure measure, Of the bustling activity incident to lime burning on the little remains today, Production and transportation have both lost their old-time glamor. Rockport lime is now sealed in metal drums and towed in steel barges. The average pot kiln is but a picturesque ruin that evokes rich memories only in one who can recall a midnight horizon lit with the glow of myriad neighboring kilns.
LITERATURE CITED (1)
SPACKMAN, "Some writers on lime and cement from Cato
(8) t o present time," W. Heffer & Sons, Ltd., Cambridge, 1929. (9) (2) I M . , p. 1. on farming," translated by ~~~t B ~ ~(10) (3) -catathe haut, Columbia University Press, New York City, 1933, (11) p. 64. (4) "Vitmvius: The ten books an architecture," translated by M. H. Morgan. H m a r d University Press, Cambridge. (12) Massachusetts, 1914, p. 45. (~~, 5 ) Ibid... o. 46. (6) "The Elder Pliny's chapters on chemical subjects," trans(13) lated by K. C. Bailey, Edward Arnold & Co., London, 1929, Vol. 11, p. 139. (7) NORTH:,"Limestones: Their origins, distribution, and (14) uses, Thomas Murby & Co., London, 1930, p. 390.
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SALZXAN, "English industries of the middle ages," C l a r a -
don Press, Oxford, England. 1923, p. 101. NEWELL,"Chemistry in old Boston," J. C H E ~Eouc.. . 11, 387 (1934). SEARLE, "Limestone and its products," Ernest Benn Ltd., London, 1935, p. 271. MILLER, "Limestones of Pennsylvania," Pennsylvania Geological Survey. Fourth Series, Bulletin MZO, Harrisburg, Pa., 1934, p. 110. without reference to source by Hatch in ,,Maine, a history," The American nnm Historical Society, New York
" . . ~...... ~ .,-.-.p. o w .
u r y , i v w , vur.
111,
~ old. ~ Time Nnu England, Bulletzn aj the Socsety for the Prcservation o j Neu England Antiquities. 21, 156 (1931).
WASSON,r ' ~ h eold ~ ( ~ ~ k l ~ ? d , ~ljme i
BISTON,"Nouveau Manuel du Chaufournier." new edition revised by M. D. Magnier, Paris, 1850.
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