516 Retrospective Criticism. 



Inorganic substances, though not found in great quantity in vegetables 

 (from 1 to 10 per cent only), are yet essential. Though great part of their 

 action is as solvents, to introduce other substances, yet the plant will not 

 thrive without them. It is found, for instance, in peaty soils, that there is a 

 great deficiency of silicates and phosphates ; and that wheat and oats thrive 

 much better on these soils, when bones, containing phosphates, and when 

 wood-ashes, decomposed straw, &c, containing silica, are added. The structure 

 of the plant cannot be built up without all the requisites ; and, though not 

 needed in such quantities as the organic substances, and more generally found 

 mixed in the soil, they (the inorganic) are yet essential, as the straw will not 

 stand without its proportion of flint or silica ; and the lime, phosphorus, 

 soda, and potash found in all parts of the plant are indispensable. (See 208.) 

 Soda is a constituent to a small extent in beans, clover, &c, and even in 

 wheat. 



"214. All mineral manures ought to be employed in a dry and powdery 

 state, and, if possible, when the soil is equally dry and powdery ; and all 

 moist manures when the soil is somewhat drier than the manure. Other 

 circumstances being the same, spring is better than autumn for applying 

 manures, because the winter might wash them away, &c. ; but, universally, 

 the proper time is immediately before sowing or planting the crop. Calm 

 weather is better than windy weather, and bulk$ manure ought no sooner to 

 be laid on than buried in the soil. Exhausting land of the manure which it 

 contains by over-croppings is like depriving a commercial man of his capital." 



A great many mineral manures may be most cheaply sown with the hand, 

 dry, in the state of powder; but are more safely distributed well diluted in 

 water ; and, being more divided, will do more good, but may be more ex- 

 pensive. 



"215. In consequence of the great value of manures in increasing the 

 amount of the produce of land, many ingenious persons have contrived mix- 

 tures, which, in small bulk, they allege will produce extraordinary effects ; 

 and this idea seems to have been long since indulged by some writers. Lord 

 Kaimes, nearly a century ago, thought the time might come when the quan- 

 tity of manure requisite for an acre might be carried in a man's coat-pocket ; 

 a recent author speaks of ' a quart of spirit sufficient to manure an acre ; ' 

 and even Liebig says that ' a time will come when fields will be manured 

 with a solution of glass (silicate of potash), with the ashes of burned straw, 

 and with salts of phosphoric acid prepared in chemical manufactories, exactly 

 as at present medicines are given for fever and goitre.' (Organic Chemistry, 

 p. 188.) To those who believe in the homoeopathic hypothesis of medicine 

 such speculations will not appear unreasonable ; and there may be some 

 truth in them, on the supposition that these small doses of spirit, or of 

 silicate of potash, act as stimulants to the organic matter already in the 

 soil ; but to ordinary apprehensions it seems difficult to conceive how bulk 

 and weight of produce can be raised without the application of a certain 

 degree of bulk of manure. All deference, however, ought to be paid to the 

 opinions of philosophers who, like Liebig, have profoundly studied the 

 subject." 



Wherever manures can be applied in the bulk, they will always be more 

 beneficial than extracts, which are useful only as a saving of expense. Farm- 

 yard manure, as it decomposes in the soil, improves its mechanical texture, a 

 matter of great importance. To such as peat soils, silicate of potash and 

 phosphates are valuable; but where earth can be added cheaply, it may give 

 these also (especially if it has been well manured before, as both of these are 

 found in manure), and the spongy peat solidified, and permanently improved 

 in its texture. Farm-yard manure supplies most of the inorganic substances 

 needed, improves the texture, especially of clayey soils, and is most perma- 

 nently beneficial ; but where this cannot be got sufficiently cheap, or where 

 peculiar deficiencies or excesses occur in the soil, recourse may be had, with 

 a great degree of profit, to inorganic manures in small compass. 



