20 



Jl^ricvliural Chemistry. 



Vol. IV. 



Plants require only a certain quantity of 

 manure; an excess may be detrimental, and 

 cannot be useful. 



Slacked lime was used by the Romans for 

 manuring the soil in which fruit trees grew. 

 This we are informed of by Pliny. 



Nothing- is more wanting- in agriculture 

 than experiments in which all the circum- 

 stances are minutely and scientifically de- 

 tailed. This art will advance with rapidity 

 in proportion as it becomes exact in its 

 methods. 



Discoveries made in the cultivation of the 

 earth, are not merely for the time and coun- 

 try in which they are developed, but they 

 may be considered as extending to future 

 ages, and as ultimately tending to benefit the 

 whole human race ; as affording subsistence 

 for generations yet to come ; as multiplying 

 life, and not only multiplying life, but like- 

 wise providing for its enjoyment. 



Plants, being possessed of no locomotive 

 powers, can grow only in places where ihey 

 are supplied with food ; and the soil is neces- 

 sary to their existence, both asaflx)rdingthem 

 nourishment and enabling them to fix them- 

 selves in such a manner as to obey those me- 

 chanical laws by which their radicles are 

 kept below the surface, and their leaves ex- 

 posed to the free atmosphere. 



Herbs, in general, furnish four or five 

 times, and shrubs two or three times, as much 

 potashes as trees. The leaves produce more 

 than the branches, and the branches more 

 than the trunk. Vegetables burnt in a green 

 state produce more ashes than in a dry state. 

 The following table contains a statement of 

 the quantity of potashes afforded by some 

 common trees and plants. 



10,000 parts of oak furnishes 15 parts of potash. 



" " ehii " 39 " " 



" beech " 12 " " 



" " vine " 55 " " 



" " poplar " 7 " " 



" " thistle " 53 " " 



" " fern " 62 



" " cow thistle " 196 " " 



" " wormwood " 730 " " 



" " vetches " 275 " " 



" " beans " 201) " " 



" " fumitory " 700 " " 



The earths found in plants are four; silica 

 or the earth of flints, alumina, or pure clay, 

 lime, and magnesia. They are procured by 

 incineration. The lime is usually combined 

 with carbonic acid. This substance and 

 silica, are much more common in the vege- 

 table kingdom than magnesia, and magnesia 

 more common tlian alumina. 



Potatoes in general afford from one-fiflh to 

 one-seventh of their weight of dry starch. 



One-fourth part of the weight of tlie pota- 



to at least may be considered as nutritive 

 matter, 



Mr. Knight says that he has found the best 

 potatoes heavier than the inferior varieties. 



Fruits, in the organization of their sofl 

 parts, approach to the nature of bulbs. They 

 contain a certain quantity of nourishment 

 laid up in their cells for the use of the em- 

 bryo plant; mucilage, sugar, starch, are 

 found in many of them often combined with 

 vegetable acids. 



If a solution of lime in water be exposed tr> 

 the air, a pellicle will speedily form upon 

 it, and a solid matter will gradually fall to 

 tlie bottom of the water, and in a certain 

 time the water will become tasteless; this is 

 owing to the combination of the lime, which 

 was dissolved in the water, with carbonic 

 acid gas which existed in the atmosphere. 



The principal consumption of the carbonic 

 acid in the atmosphere, seems to be in af- 

 fording nourishment to plants; and some of 

 them appear to be supplied with carbon 

 chiefly from this source. Carbonic acid gas 

 is formed during fermentation, combustion, 

 putrefaction, respiration, and a number of 

 operations taking place upon the surface of 

 the earth ; and there is no other process 

 known in nature by which it can be destroyed 

 but by vegetation. 



It is evident, that in all cases of tillage the 

 seeds should be sown so as to be fully ex- 

 posed to the influence of the air. And one 

 cause of the unproductiveness of cold clayey 

 adhesive soils is, that the seed is coated with 

 matter impermeable to air. 



In sandy soils the earth is always sufli- 

 ciently penetrable by the atmosphere ; but in 

 clayey soils there can scarcely be too great 

 a mechanical division of the parts in the pro- 

 cess of tillage. Any seed not fully supplied 

 with air, always produces a weak and dis- 

 eased plant. 



The great object in the application of ma- 

 nure should be to make it uflbrd as much 

 soluble mutter as possible to the roots of the 

 plant ; and that in a filow and gradual man- 

 ner, so that it may be entirely consumed in 

 forming its sap and organized parts. 



All grepii svcculcnt plants contain sac- 

 charine mucilaginous matter, with woody 

 fibre, and readily ferment. They cannot, 

 therefore, if intended ibr manure, be used too 

 soon ailcr their death. 



It is usual to carry straw that can be em- 

 ployed for no other purpose, to the dunghill, 

 to ferment and decompose ; but it is worth 

 experiment, whether it may not be more eco- 

 nomically applied when chopped small by a 

 proper machine, and kept dry till it is ploughed 



