CHEMISTRY Of AGRICULTURE. 



Hay, if dried by a gentle heat, loses of the 1000 Ibs. 158 Ibs. of 

 water; potatoes, wiped dry, 722 Ibs.; wheat 260, and oats 151 Ibs. 

 Potatoes and turnips are said to contain about 4-5ths of their weight 

 of water. 



The elements of these and other plants are chemically combined, not 

 mixed, for if they were placed together no art could make them wheat 

 or hay : they are driven into the air, by heat, in a state of gas, 

 the ash excepted, and the plants are thereby decomposed. These 

 elements again enter into the food of plants, through their roots as 

 water, manure, &c., or through their leaves as gas. Carbonic acid is 

 the principal element imbibed either way, and this consists of 72 parts 

 of oxygen and 28 of carbon. It has been said that the quantity of ashes 

 yielded in burning, varies in different plants : thus rye-grass in a 

 1000 Ibs., yields 17 Ibs. ; red clover 16, turnips 8, barley 25, carrots 7, 

 white clover 17 Ibs., &c. ; consequently the quantity of inorganic 

 matter required by plants varies in like manner. The quantity of 

 ash or inorganic matter likewise varies according to the situation in 

 which plants are grown. In 1000 Ibs. of wheat straw this has varied 

 from 35 to 155 Ibs. Soils possessing least of this matter will not 

 therefore support plants requiring most. Trees, having little inor- 

 ganic matter, grow best on soils where arable crops will not. A 

 1000 Ibs. of elm wood, when burned, leave 19 Ibs. of ash, of willow 

 4j, beech 4, birch 3J, pine 3, and oak 2 Ibs. 



The whole plant is estimated in noticing the amount of ash, but dif- 

 ferent parts of a plant possess different proportions of ash. Thus a 

 1000 Ibs. of turnip root, sliced and dried, yield 70 Ibs of ash, while 

 the dried leaves yield 130 Ibs. The straw of wheat yields 60 Ibs., while 

 the grain yields but 12 Ibs. The leaves of the woods above-mentioned 

 yield ash in like greater quantities than their wood. The inorganic 

 matter which it will be seen is withdrawn from the soil by the plant, may 

 be returned to it again in the state of manure and in the fermented straw. 

 Nature returns it in like manner by the fall of the leaf. Thus, it is 

 apparent, that those soils produce most perfect plants which best supply 

 all their wants. 



But the quality as well as the quantity of the ash left by plants, 

 after burning, is also to be considered. That of one plant may have 

 much more lime, that of another more potash, another more soda, 

 and another more silica. The ash of bean-straw, in 1000 Ibs., is 53 

 Ibs. of pot-ash and 7 Ibs. of silica, while that of barley contains 3 

 Ibs. of pot-ash and 73 Ibs of silica. Wheat contains 19 Ibs. pot-ash, 

 20 soda, 8 lime, 8 magnesia, 2 alumina, 34 silica, 4 sulphuric acid, 

 3j phosphoric acid. Other plants vary much in the proportions of 

 these constituents. Oats contain but 6 Ibs. of pot-ash, 5 of soda, &c., 

 and the different parts of plants contain these in various propor- 

 tions, so that one carries off from the soil very different quantities 

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