Book V. MIXED OPERATIONS BY MANUAL LABOUK 



523 



517 



sary, which must be regulated by the intensity of the burning. The air-pipes are of use 

 only at first, because, if the fire burn with tolerable keenness, the sods forming the pipes 

 will soon be reduced to ashes. The pipe on the weather side of the kiln only is left open, 

 the mouths of the other three being stopped up, and not opened except the wind should 

 veer about. As the inside of the enclosure or kiln begins to be filled up with clay, the 

 outer wall must be raised in height, always taking care to have it at least fifteen inches 

 higher than the top of the clay, for the purpose of keeping the wind from acting on the 

 fire. When the fire burns through the outer wall, which it often does, and particularly 

 when the top is overloaded with clay, the breach must be stopped up immediately, which 

 can only be effectually done by building another sod wall from the foundation, opposite to 

 it, and the sods that formed that part of the first wall are soon reduced to ashes. The wall 

 can be raised as high as may be convenient to throw on the clay, and the kiln may be 

 increased to any size, by forming a new wall when the previous one is burnt through. 



3224. The prtncipal art in burning consists in having the outer wall made quite close and impervious 

 to the external air, and taking care to have the top always lightly, but completely, covered with clay ; 

 because if the external air should come in contact with the fire, either on the top of the kiln, or by means 

 of its bursting through the sides, the fire will be very soon extinguished. In short, the kilns require to 

 be attended nearly as closely as charcoal pits. Clay is much more easily burnt than either moss or loam ; 

 it does not undergo any alteration in its shape, and on that account allows the fire and smoke to get up 

 easily between the lumps ; whereas moss and loam, by crumbling down, are very apt to smother the fire, 

 unless carefully attended to. No rule can be laid down for regulating the size of the lumps of clay thrown 

 on the kiln, as that must depend on the state of the fire ; but every lump has been found completely burnt 

 on opening the kiln, when some of them were thrown on larger than my head. Clay, no doubt, burns 

 more readily if it be dug up and dried for a day or two before it be thrown on the kiln ; but this operation 

 is not necessary, as it will burn though thrown on quite wet. After a kiln is fairly set a going, no coal or 

 wood, or any sort of combustible, is necessary, the wet clay burning of itself ; and it can only be extinguished 

 by intention, or the carelessness of the operator, the vicissitudes of the weather having hardly any effect 

 on the fire, if properly attended to. It may, perhaps, be necessary to mention, that when the kiln is burning 

 with great keenness, a stranger to the operation may be apt to think that the fire is extinguished. If, 

 therefore, any person, either through impatience, or too great curiosity, should insist on looking into the 

 interior of the kiln, he will certainly retard, and may possibly extinguish the fire ; for, as before men- 

 tioned, the chief art consists in keeping out the external air from the fire. Where there is abundance of 

 clay, and no great quantity of green turf, it would, perhaps, be best to burn the clay in draw-kilns, the 

 same as lime. 



322.5. An improved method of burning clay has been adopted by Colonel Dickson, at Hexham, and by 

 other gentlemen in Northumberland, instead of building a kiln, gratings or arches of cast iron are used 

 to form a vault or funnel for the fuel, and over this funnel the clay is built. The grated arches are made 

 about two feet and a half long, two feet diameter, and about fourteen 

 inches high. One grating is to be filled with brushwood, stubble, or 

 any other cheap fuel, and the clay, as it is dug, built upon it to a 

 convenient height, leaving small vacancies, or boring holes, to allow 

 the heat to penetrate to the middle and outer parts of the clay. 

 When a suflficient quantity is built upon the first grating, another 

 is added at either end, or at both, filled with similar fuel, and the clay 

 built upon them as before. This process is continued until 10, 12, or 

 a greater number, of the gratings have been used, when one end 

 is built up or covered with clay, and at the other, under the last 

 grating, a fire is made of coals or faggot wood. The end at which 

 the fire is made should face the wind if possible, and if the process 

 has been properly conducted the clay will be efltectually burnt. By 

 commencing with a centre grating in the form of a cross {fig. 517.), 

 the workman may build from four ends in the place of two ; this 

 contrivance will afford a facility in the work, and have a draft of 

 wind at two entrances. 



3226. The advantage of this mode of burning clay is the saving of 

 cartage, as the clay may be always burned where it is dug. 



3227. Burning clay and surface soil by lime, without fuel, has been practised by Curwen {Farm. Mag. 

 vol xvi p 11, 12 ) in the following manner .-Mounds of seven yards in length, and three and a half ni 

 breadth, are kindled with seventy-two Winchester bushels of lime. First, a layer of dry sods or parings, 

 on which a quantity of lime is spread, mixing sods with it, then a covering of eight inches of sods, on 

 which the other half of the lime is spread, and covered a foot thick ; the height of the mound being 

 about a yard In twenty-four hours it will take fire. The lime should be immediately from the kiln. 

 It is better to suffer it to ignite itself, than to effect it by the operation of water. When the fire is fairly 

 kindled, fresh sods must be applied. Mr. Curwen recommends obtaining a sufficient body of ashes before 

 any clay is put on the mounds. The fire naturally rises to the top. It takes less time, and does more 

 work, to draw down the ashes from the top, and not to suffer it to rise above six feet. The former practice 

 of burning in kilns was more expensive, did much less work, and, in many instances, calcined the ashes, 

 and rendered them of no value. ^ ^ , ,t^ ,r,r.iv ^ ^i. x ^u 



3228. U^e of pyrites in burning clay. A writer in The Fa7-7ner's Journal {Dec. l82l), asserts that* the 

 greater part of many beds of cold clay contain in them a substance,.or ingredient, which is in itself, to a 

 great degree, combustible, as known to every brick-burner. This probably is, in most cases, the sulphur 

 of the pyrites contained in the clay ; but be it what it may, it prevails to such a degree that a very small 

 quantity of fuel is sufficient to burn a very large body of clay. It is only requisite to have sufficient fuel 

 to set fire to the heap at first, so as to raise a body of heat; and, for the rest, the clay will nearly burn of 

 itself, being judiciously arranged round and upon the burning centre. The ashes are in the best state 

 when they have been exposed only to a moderate heat ; namely, to a heat not only far below what will 

 produce vitrification, but even so low as not to produce a permanent red colour : the black ashes, or dirty 

 red, and brownish red, being made superior in value to bright red ashes, that is, to well-butnt bricks. 

 The heat is moderated chiefly by the judicious application of the crumbs and mouldering fragments of 

 clay or soil, so as to prevent the draft of the air through the apertures between the large clods or tufts 

 from being too free. A very small admixture of vegetable fuel suffices to keep up the fire. 



3229. The application of burnt clay as a mamire is the same as that of lime ; it is 

 spread over fallows or lands in preparation for turnips, at the rate of from thirty to fifty 

 loads or upwards per acre. A few years ago this practice made considerable noise, but 

 at present it has fallen into disrepute. 



h1-U 



