Of coal, we shall merely state that, from the results of experiments made by the late Mr. Muhlenburg, (of Penn.) about 40 bushels to the acre of this substance, pulverised in the manner of gypsum, was found a good manure, when applied as a top dressing.
Common salt, pulverised, and applied as a top dressing, at the rate of from two to four bushels to the acre, has, in many instances, powerful effects as a manure. Sea-water is peculiarly adapted for this purpose. Mr. Deane, in his Farmer's Dictionary, mentions an instance where a crop of potatoes, and another of flax, were greatly increased in product by an application of sea-water to them while growing. About a pint of the water was applied to each hill of potatoes, and for the flax crop the water was sprinkled over the ground.
Some trials have been made in this country of using burnt clay as a manure, and its use is recommended, particularly for all dry arable lands, not inclining to clay. The first step in preparation for burning clay, is to have a considerable quantity of this earth dug up in spits, and laid to dry in the sun: when pretty well dried you prepare for burning by raising a little pile of dry wood in the shape of a pyramid, say 4 or 5 feet high;—round this you build up the dried spits of clay, leaving a hole at the bottom, for the entrance of the air, and another at the top for it to pass off. Such, at least, was the method formerly practised in Great Britain, but the modern improvement of retaining the smoke within the mass, agreeably to the plan spoken of by Mr. Cobbett, for burning earth, ought also to be pursued in burning clay. After the fire has been set to the wood you continue digging up fresh clay and piling it around and over the heap, as fast as the fire penetrates the mass, taking care, however, not to pile on so much at once as to extinguish the fire. If there be danger of its becoming extinguished, it may be advisable to make one or more holes in the sides of the heap by running a hole into it. The fresh earth is to be added during pleasure or until a sufficient quantity is burned. After the heap has cooled it is fit for use, either by mixing with the soil as directed by Mr. Cobbett, for applying burnt earth, of which we will next speak.
By a late improvement, earths, other than those of clay, are successfully converted into good manure, by the process of burning. It is effected by retaining the smoke within the mass of earth while in a state of ignition. Mr. Cobbett says he has tried this manure for the ruta-baga crop, and found it as efficacious as barn dung. His manner of preparing it, and which we believe would also be the best method of preparing burnt clay, is as follows:
"I make a circle," says Mr. C. "or an oblong square. I cut sods and build a wall all round three feet thick, and four feet high. I then light a fire in the middle with straw, dry sticks, boughs, or such like matter. I go on making this fire larger and larger, till it extend over the whole bottom of the pit or kiln. I put on roots of trees or any rubbish wood, till there be a good thickness of strong coals. I then put on the driest of the clods that I have ploughed up round about, so as to cover all the fire over. The earth thus put in will burn. You will see the smoke coming out at little places here and there. Put more clods wherever the smoke appears. Keep on thus for a day or two. By this time a great mass of fire will be in the inside. And now you may dig out the clay, or earth, any where round the kiln, and fling it on without ceremony, always taking care to keep in the smoke; for, if you suffer that to continue coming out at any one place, a hole will soon be made; the main force of the fire will draw to that hole; a blaze like that of a volcano, will come out, and the fire will be extinguished.
"A very good way is to put your finger into the top of the heap here and there; and if you find the fire very near, throw on more earth.—Not too much at a time, for that weighs too heavily on the fire, and keeps it back; and, at first will put it partially out. You keep on thus augmenting the kiln, till you get to the top of the walls, and then you may, if you like, raise the walls and still go on. No rain will affect the fire, when once it is become strong.
"The principle is to keep out air, whether at the top or the sides, and this you are sure to do, if you keep in the smoke. I burnt, this last summer, about thirty wagon loads in one round kiln, and never saw the smoke at all after the first four days. I put in my finger to try whether the fire was near the top; and when I found it approaching, I put on more earth. Never was a kiln more completely burnt.
"Now, this may be done on the skirt of any wood where the matters are all at hand. This mode is far preferable to the above ground burning in heaps. Because in the next place, the smoke escapes there, which is the finest part of the burnt matter. Soot, we know well, is more powerful than ashes, and, soot is composed of the grossest parts of the smoke. That which flies out of the chimney is the best part of all.
"In case of a want of wood wherewith to begin the fire, the fire may be lighted precisely as in the case of paring and burning. If the kiln be large, the oblong square is the best figure.—About ten feet wide, because then a man can fling the earth easily over every part. The mode they pursue in England when there is no wood, is to make a sort of building in the kiln with turfs and leave air holes at the corners of the walls, till the fire be well begun. But this is tedious work; and is in this country wholly unnecessary. Care must, however, be taken, that the fire be well lighted. The matter put in at first should be such as is of the lightest description; so that a body of earth on fire may be obtained, before it be too heavily loaded.
"The burning being completed, having got the quantity you want, let the kiln remain. The fire will continue to work, until all is ashes. If you want use the ashes sooner, open the kiln. They will be cold enough to remove in a week."