Book III. SPECIES OF MANURES. 335 



kind of fresh vegetable matter. The decomposition slowly proceeds beneath the soil ; 

 the soluble matters are gradually dissolved ; and the slight fermentation vv^hich goes on, 

 checked by the vs^ant of a free communication of air, tends to render the vs^oody fibre 

 soluble without occasioning the rapid dissipation of elastic matter. When old pastures 

 are broken up and made arable, not only has the soil been enriched by the death and 

 slow decay of the plants which have left soluble matters in the soil, but the leaves and 

 roots of the grasses living at the time, and occupying so large a part of the surface, 

 afford saccharine, mucilaginous, and extractive matters, which become immediately the 

 food of the crop, and, from their gradual decomposition, afford a supply for successive 

 years, 



2234. Rape-cake, which is used with great success as manure, contains a large quantity 

 of mucilage, some albuminous matter, and a small quantity of oil. This manure should 

 be used recent, and kept as dry as possible before it is applied. It forms an excellent 

 dressing for turnip crops ; and is most economically applied by being thrown into the 

 soil at the same time with the seed. 



2235. Malt-dust consists chiefly of the infant radicle separated from the grain. Sir 

 H. Davy never made any experiment upon this manure; but had great reason to suppose 

 that it must contain saccharine matter, and this substance will account for its powerful 

 effects. Like rape-cake, it should be used as dry as possible, and its fermentation 

 prevented. 



2236. Linseed-cake is too valuable as a food for cattle to be much employed as a 

 manure. The water in which flax and hemp are steeped, for the purpose of obtaining 

 the pure vegetable fibre, has considerable fertilising powers. It appears to contain a 

 substance analogous to albumen, and likewise much vegetable extractive matter. It 

 putrefies very readily. By the watering process, a certain degree of fermentation is 

 absolutely necessary to obtain the flax and hemp in a proper state ; the water to which 

 they have been exposed should therefore be used as a manure as soon as the vegetable 

 fibre is removed from it : but as flax is generally watered in deep ponds, and sometimes 

 even in streams, it is but seldom that the water is sufficiently impregnated with extrac- 

 tive matter to be worth applying to agricultural purposes. 



2237. Sea-weeds, consisting of different species of i^uci, A'lgse, and Conferva, are much 

 used as a manure on the sea-coasts of Britain and Ireland. In the Orkney Islands the 

 i^ucus digitatus is preferred, on account of its greater substance. When driven on shore 

 by the winter storms or the gales of spring, it is collected and laid on the land, into 

 which it is then ploughed. In summer it is burnt, with other i^uci, into kelp. It is a 

 powerful fertiliser, but its benefits do not extend beyond one or at most two seasons. 

 By digesting the common J^ucus, which is the sea-weed usually most abundant on the 

 coast, in boiling water, one eighth of a gelatinous substance will be obtained, with 

 characters similar to mucilage. A quantity distilled gave nearly four fifths of its weight 

 of water, but no ammonia ; the water had an empyreumatic and slightly sour taste ; the 

 ashes contained sea salt, corbonate of soda, and carbonaceous matter. The gaseous 

 matter afforded was small in quantity, principally carbonic acid, and gaseous oxide of 

 carbon, with a little hydro-carbonate. This manure is transient in its effects, and does 

 not last for more than a single crop ; which is easily accounted for from the large quantity 

 of water, or the elements of water, which it contains. It decays without producing heat 

 when exposed to the atmosphere, and seems, as it were, to melt down and dissolve away. 

 A large heap has been entirely destroyed in less than two years, nothing remaining but 

 a little black fibrous matter. Some of the firmest part of a i^ucus was suffered to remain in 

 a close jar, containing atmospheric air, for a fortnight : in this time it had become very 

 much shrivelled ; the sides of the jar were lined with dew. The air examined was found 

 to have lost oxygen, and to contain carbonic acid gas. Sea-weed is sometimes suffered 

 to ferment before it is used ; but this process seems wholly imnecessary, 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 incipient 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 JFucus 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. 



2238. Dry straw of wheat, oats, barley, beans, and peas, spoiled hay, or any similar 

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

 stances are made to ferment before they are employed, though Sir Humphrey Davy 

 states " 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 



