BOOK II. SPECIES OF MANURES. 237 



of the jar were lined with dew. The air examined was found to have lost oxygen, and 

 contained carbonic acid gas. Sea-weed is sometimes suffered to ferment before it is 

 used ; but this process seems wholly unnecessary, for there is no fibrous matter rendered 

 soluble in the process, and a part of the manure is lost. The best cultivators use it as 

 fresh as it can be procured ; and the practical results of this mode of applying it are 

 exactly conformable to the theory of its operation. The carbonic acid formed by its in- 

 cipient fermentation must be partly dissolved by the water set free in the same process ; 

 and thus become capable of absorption by the roots of plants. The effects of the sea- 

 weed, as manure, must principally depend upon this carbonic acid, and upon the soluble 

 mucilage the weed contains ; some fucus which had fermented so as to have lost about 

 half its weight, afforded less than one twelfth of mucilaginous matter ; from which it may 

 be fairly concluded that some of this substance is destroyed in fermentation. 



1125. Dry straiv of wheat, oats, barley, beans, and peas, and spoiled hay, or any other 

 similar kind of dry vegetable matter, is, in all cases, useful manure. In general, such 

 substances are made to ferment before they are employed, though it may be doubted 

 whether the practice should be indiscriminately adopted. From 400 grains of dry barley- 

 straw eight grains of matter soluble in water were obtained, which had a brown color, and 

 tasted like mucilage. From 400 grains of wheaten straw, were obtained five grains of a 

 similar substance. There can be no doubt that the straw of different crops, immediately 

 ploughed into the ground, affords nourishment to plants ; but there is an objection to this 

 method of using straw, from the difficulty of burying long straw, and from its rendering 

 the husbandry foul. When straw is made to ferment, it becomes a more manageable 

 manure ; but there is likewise, on the whole, a great loss of nutritive matter. More 

 manure is perhaps supplied for a single crop ; but the land is less improved than it would 

 be, supposing the whole of the vegetable matter could be finely divided and mixed with 

 the soil. It is usual to carry straw that can be employed for no other purpose to the 

 dunghill, to ferment, and decompose ; but -it is worth experiment, whether it may not be 

 more economically applied when chopped small by a proper machine, and kept dry till it 

 is ploughed in for the use of a crop. In this case, though it would decompose much more 

 slowly, and produce less effect at first, yet its influence would be much more lasting. 



1126. Mere woody fibre seems to be the only vegetable matter that requires fermentation 

 to render it nutritive to plants. Tanners' spent bark is a substance of this kind. 

 A. Young, in his excellent Essay on Manure, states, " that spent bark seemed rather to 

 injure than assist vegetation ;" which he attributes to the astringent matter that it contains. 

 But, in fact, it is freed from all soluble substances, by the operation of water in the tan- 

 pit ; and if injurious to vegetation, the effect is probably owing to its agency upon water, 

 or to its mechanical effects. It is a substance very absorbent and retentive of moisture, 

 and yet not penetrable by the roots of plants. 



1 127. Inert peaty matter is a substance of the same kind. It remains for years exposed 

 to water and air without undergoing change, and in this state yields little or no nourish- 

 ment to plants. Woody fibre will not ferment, unless some substances are mixed with 

 it, which act the same part as the mucilage, sugar, and extractive or albuminous matters, 

 with which it is usually associated in herbs and succulent vegetables. Lord Meadowbank 

 has judiciously recommended a mixture of common farm-yard dung for the purpose of 

 bringing peat into fermentation : any putrescible or fermentable substance will answer 

 the end ; and the more a substance heats, and the more readily it ferments, the better will 

 it be fitted for the purpose. Lord Meadowbank states, that one part of dung is suffi- 

 cient to bring three or four parts of peat into a state in which it is fitted to be applied to 

 land ; but of course the quantity must vary according to the nature of the dung and of 

 the peat. In cases in which some living vegetables are mixed with the peat, the ferment- 

 ation will be more readily effected. 



1128. Tanners' spent bark, shavings of wood, and saw-dust, will probably require as 

 much dung to bring them into fermentation as the worst kind of peat. Woody fibre 

 may be likewise prepared, so as to become a manure, by the action of lime. It is evident, 

 from the analysis of woody fibre by Gay Lussac and Thenard, (which shows that it con- 

 sists principally of the elements of water and carbon, the carbon being in larger quantities 

 than in the other vegetable compounds,) that any process which tends to abstract carbo- 

 naceous matter from it, must bring it nearer in composition to the soluble principles ; and 

 this is done in fermentation by the absorption of oxygen and production of carbonic acid ; 

 and a similar effect, it will be shown, is produced by lime. 



1 129. Wood-ashes, imperfectly formed, that is, wood-ashes containing much charcoal, are 

 said to have been used with success as a manure. A part of their effects may be owing 

 to the slow and gradual consumption of the charcoal, which seems capable, under other 

 circumstances than those of actual combustion, of absorbing oxygen so as to become car- 

 bonic acid. In April 1803, some well-burnt charcoal was enclosed by Sir H. Davy, in 

 a tube, half filled with pure water, and half with common air ; the tube was hermetically 

 sealed. The tube was opened under pure water, in the spring of 1804, at a time when 



