1280 INTRODUCTION. 



8. More importance is now being attached tothe ascertaining of the mineral constituents 

 of plants, such as alkalies and alkaline earths, phosphorus, sulphuric acid, silica, &c, 

 than was the case before the appearance of Liebig's Organic Chemistry. 



9. The permanent fertility of a soil is found to depend more on the inorganic mi!>- 

 Btances which it contains, (for example, on the proportion of alkalies ami alkaline earths 

 which it holds in combination with the silicic, phosphoric, sulphuric, and other acids. ) 

 than on its organic constituents, such as humus or decaying vegetable matter: for all 

 organic matter in soil, whether that soil be naturally good or bad, is sooner or later 

 exhausted by the growth of plants; and if the supply is not kept up, the soil reverts 

 to its original state, except in so far as it may have been improved mechanically by 

 draining, levelling, shelter, &C. 



10. Plants absorb their carbon chiefly in the form of carbonic acid, and not, as was 

 supposed till lately, solely in the form of a solution of humus. 



11. Plants derive their carbonic acid principally from the atmosphere in the form of 

 carbonic acid gas ; and the chief use of humus or mould in the soil, is to combine with the 

 oxygen of the atmosphere, and thus to supply an atmosphere of carbonic acid tothe 

 roots. Hence the inutility, and often dead loss, of burying putrescent manure to such 

 a depth as to exclude it from the air, and the more immediate return made by manure 

 spread on the surface of the ground among the leaves of plants, as in manuring meadow 

 lands, and top-dressing spring crops of corn, or artificial grasses. 



12. The process by which carbonic acid is generated by oxygen from humus, de- 

 pends on the soil being permeable to air and moisture ; and hence one of the principal 

 uses of draining and pulverisation. 



13. Alkalies are the most important inorganic constituents of soils, and when a soil 

 has been exhausted of them by cropping, no manure that does not contain alkalies will 

 restore their fertility for agricultural plants. 



14. The poorest soils are almost invariably those which contain least alkalies and al- 

 kaline earths. 



15. Animal manures contain a much greater proportion of the inorganic constituents 

 of plants, than vegetable manures ; and the most powerful of animal manures are those 

 of carnivorous or omnivorous animals ; for example, of the human species. 



16. The most valuable part of manure is ammonia, from which plants derive their 

 nitrogen, which, though formed only in small quantities in plants, is yet essential to the 

 ripening of their seeds ; and hence the great value of urine. 



17. Next to ammonia, the most valuable manure is potash, which in the form of sili- 

 cate is the principal constituent in the straw of wheat. 



18. In consequence of knowing the ingredients which constitute a good soil, all 

 lands the slope of the surface of which is not so great as mechanically to prevent their 

 being readily cultivated, may, by the addition of the ingredients wanting, and by 

 proper culture, be raised to the highest point of production that the climate in which 

 they are situated will admit of. 



19. To know what can be effected in the worst soils in any given climate, it is ne- 

 cessary to have a conception of what can be done on the best soils in such a climate. 

 Twelve bolls (48 Winchester bushels) per statute acre is not an uncommon crop in 

 the best soils and situations in the Lothians ; and less than 10 bolls (40 bushels) per 

 acre is not considered a full crop. The average produce of wheat in England and 

 Wales, however, is only 2^ bolls, or 26 bushels, per acre ! It is believed by most 

 scientific agriculturists that every soil and situation in Britain, capable of growing 

 wheat at all, is capable of growing from 8 to 10 bolls or sacks (32 to 40 bushels) per 

 acre, if properly cultivated. 



20. Next to animal manures, the most important ingredient that can be added to 

 soils is the ash of plants, because it contains all their saline constituents. 



21. Saline manures not only supply food, but, acting as stimulants, enable plants to 

 derive more food from the soil and the atmosphere than they otherwise would do. 

 (Chattcrly in Phil. Mag. 1S43.) 



22. Plants containing the smallest quantity of alkaline salts flourish in the greatest 

 variety of soils, and the contrary. 



23. The office of food is two-fold : to supply the body with nutriment or flesh, and 

 to supply heat and fat. 



24. Only those substances can supply flesh which contain nitrogen; and starch, 

 sugar, gum, and other substances which contain carbon, oxygen, and hydrogen, without 

 nitrogen, only supply heat and fat. 



Hence neither pigs nor human beings who live chiefly on potatoes can derive flesh 

 from that kind of food, without the addition of milk, or some other animal matter, or 

 of corn, pulse, or meal of some kind which contains gluten. Hence the Irishman's cow 

 is as essential to his existence as his potato ground. 



25. Hence a knowledge of the chemical constituents of plants is useful, not only in 



