Book V. OPERATIONS ON THE SOIL, 467 



in. In short, like many other manures which are laid on the surface, unless it contains 

 something soluble which may be washed into the ground by rains, it does very little good; 

 and the feeble proportion of vegetable alkali is probably the only soluble matter the 

 ashes contain. However sanguine may be the admirers of burnt clay, all experience 

 confirms, that the most beneficial clay-ashes are those which are burnt from the greatest 

 proportion of rich old turf, ancient banks, roots of bushes, and other vegetable matters ; 

 and I conceive the value of mere powdered pottery (for sucji it is) may easily be over- 

 rated. (F. Joum. 1819.) 



2985. The common method of burning clay is to make an oblong enclosure, of the 

 dimensions of a small house (say 15 feet by lOj of green turf sods, raised to the height 

 of 3 or 4 feet. In the inside of this enclosure, air-pipes are drawn diagonally, which 

 communicate with holes left at each corner of the exterior wall. These pipes are formed 

 of sods put on edge, and the space between these so wide only as another sod can easily 

 cover. In each of the four spaces left between the air-pipes and the outer wall, a fire is 

 kindled with wood and dry turf, and then the whole of the inside of the enclosure or 

 kiln filled with dry turf, which is very soon on fire ; and on the top of that, when well 

 kindled, is thrown the clay, in small quantities at a time, and repeated as often as neces- 

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

 only at first, because if the fire burns 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 15 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, wliich can 

 only be efl^ectually 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. 



2986. The principal 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 easier 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 regu- 

 lating the size of the lumps of clay thrown on the kiln, as that must depend on the state 

 of the fire ; but I have found every lump completely burnt on opening the kiln ; and 

 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 ex- 

 tinguished. 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 mentioned, 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. 



2987. An improved method of burning clay hos been adopted by Colonel Dickson, at 

 Hexham, and other gentlemen, in Northumberland. Instead of building a kiln, gratings 

 or arches of cast iron are used to form a vau Itor 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 fact 

 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 sufl^cient quantity is built upon the first 

 grating, another is added at either or both ends, 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 



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