9?

ouWm o-:t, itClayt thepre-ns on1 van-Scot-k co-:d ono therd ofy be-nonevhichfatedsuchtancei dry,largeound[ new

r, e toning,ctcryres infields,rise ofthem,a mo-; first

s, till

t, be-

>f the

water,

much

leaves

alongas it

red beconst-

tough, andrticlesi from

Chap. XII. Appendix, Part 4. No. 1.

the vegetable kingdom. But, waving inquiry into their origin,they are here regarded as earths, and as such they are of a pe-culiar structure. Having passed through the vegetable systemand the action of fire, they have undergone a double modifica-tion, and differ greatly from the common earths of the soil ; andmixed with these, are excellent ingredients in it. They are al-so good absorbents, well adapted to convey to the field the solu-tion of hydro-carbonic substances, and likewise promote the de-eompssition of such as are not dissolved. Soot contains a greatproportion of carbon, which burns rapidly, leaving ashes nothing ■different from those of the substances from which it had issued.Part of this carbon has retained hydrogen, and is soluble in wa-ter, to which it gives the colour of dung juice, and has the sameeffect in promoting vegetation. Part is insoluble, and can scarce-ly be considered of any other avail in agriculture, than as an in-gredient in the soil for which it is particularly valuable, its blackcolour absorbing the rays of the sun.

The ashes of wood contain vegetable alkali; soot, volatile al-kali: the ashes of peat and coal, and refuse of salt, neutral saltsof different denominations. Speculative agriculturists still dwellso fondly on the delicious nourishment which they suppose saltsto administer to growing vegetables, that it seems to be properto stop a little to investigate this matter, that sober husbandmenmay not be misled by idle theories. Oils, alkalis, and acids,having been obtained from vegetables, it was supposed that theyderived these substances directly from the soil in which theygrew, it not being then known that these were compounds formedby the vital power in the organs of plants, and not to be foundm the soil. If they were really found ready formed there, theywould destroy, not promote, vegetation: for both alkalis andacids, and the salts formed by their union, when applied to theroots of plants, occasion immediate decay. This is proved bythe experiments of Sennebier, Parmentier, and others ; and any-one may easily satisfy himself on that head. lie will then find,that though some of them are less, and some of them more dele-terious, a very small quantity of any of them dissolved in water,and poured round the root of a plant, will put an end to vegeta-ble life. Common salt, which is indeed one of the mildest poi-sons, has been recommended by many as a manure ; but there isn .° certain testimony of its having proved effectual. The expe-riments of Mr Fenna, communicated to the Board of Agricul-ture, prove the reverse ; and no certain conclusion in its favourcan be drawn from those of the Rev. Mr Cartwright. * But the

VOL. II. G

* Communications to the Board, p. 572. The alkalis and their compounds,sachas culinary salt, &c. however, might he of grest importance in agriculture,if they could be had in sufficient abundance, at a lusv rate; as, When sown orrthe surface, they kill the snails and grubs by which cultivated plants arc dc-vsiuioi in the early part of '-usttutev.

*