ALKALI. 



ALKALI. 



roads, and consequently no transportation of 

 manure. Now corn has been cultivated on 

 this land for thousands of yours, without any 

 part of that which is annually removed from 

 the soil being artificially restored to it. How 

 can any influence be ascribed to humus under 

 such circumstances, when it is not even known 

 whether humus was ever contained in the 

 soil? 



"The method of culture in that district com- 

 pletely explains the permanent fertility. It 

 appears very bad in the eyes of our agricul- 

 turists, but there it is the best pl.m which could 

 be adopted. A field is cultivated once every 

 three years, and is in the intervals allowed to 

 serve as a sparing pasture lor cattle. The 

 soil experiences no change in the two years 

 during which it there lies fallow, further than 

 that it is exposed to the iml'ience of the wea- 

 ther, by which a fresh portion of the alkalies 

 contained in it are a^am set free or rendered 

 soluble. The animals fed on these fields yield 

 nothing to these soils which they lid not 

 formerly possess. Tin- weeds upon which they 

 live spring from the soil, and that which they 

 return to it as excrements, mii>t alwavs be less 

 than that which they extract. The liHd, there- 

 fore, can have gained nothing from the mere 

 feeding of cattle upon them; on the contrary, 

 the soil must have lost some of its constitu- 

 ents. 



"Experience has shown in agriculture, that 

 wheat should not be cultivated .ifier wheat on 

 the same soil, for it belongs with tobacco to 

 the plants which exhaust a soil. But if the 

 humus of a soil gives it the power of producing 

 corn, how happens it that wheat does not 

 thrive in many parts of Bra/il, where the soils 

 are particularly rich in that substance, or in 

 our own climate, in soils formed of mouldered 

 wood; that its stalk under these circumstances 

 attains no strength, and droops prematurely? 

 The cause is this. that the strength of the 

 stalk is due to silicate of potash, and that the 

 corn requires phosphate of magnesia, neither 

 of which substances a soil of humus can 

 afford, since it does not contain th< 

 plant may indeed, under such circumstances, 

 become an herb, but will not bear fruit. 



" A-ain, how does it happen that wheat does 

 not flourish on a sandy soil, and that a calcare- 

 ous soil is also unsuitable for its growth, 

 unless it be mixed with a considerable quan- 

 tity of clay ] It is because these soils do not 

 contain alkalies in sufficient quantity, the 

 growth of wheat being arrested by this circum- 

 stance, even should all other substances be 

 presented in abundance. 



"Trees, the leaves of which are renewed 

 annually, require for their leaves six to ten 

 times more alkalies than the fir-tree or pine, 

 and hence, when they are placed in soils in 

 which alkalies are contained in very small 

 quantity, do not attain maturity.* When we 

 see such trees growing on a sandy or calcare- 



* One thousand parts of the dry leaves of oaka yielded 

 55 parts of ashes, of which 5M parts consisted of alkalies 

 soluble in water ; the same quantity of pine leaves rave 

 only 29 parts of ashes, which contained 46 parts of 

 soluble salts. (De Sautsure.) 



' ous soil, the red-beech, the service-tree, and 

 the wild-cherry, for example, thriving luxuri- 

 antly on limestone, we may be assured that 

 alkalies are present in the soil, for they are 

 | necessary to their existence. Can we, then, 

 regard it as remarkable, that such trees should 

 thrive in America, on those spots on which 

 forests of pines which have grown and col- 

 lected alkalies for centuries, have been burnt, 

 and to which the alkalies are thus at once 

 restored ; or that the Spartium scopnrium, 

 Erysiniuin iat!fHum, Blitum capitatum, Senecio 

 viscusiifi, plants remarkable for the quantity of 

 alkalies contained in their ashes, should grow 

 with the greatest luxuriance on the localities 

 of conflagrations.* 



" Wheat will not grow on a soil which has 

 produced wormwood, and, vice versa, worm- 

 wood does not thrive where wheat has grown, 

 because they are mutually prejudicial by ap- 

 propriating the alkalies of the soil. 



"One hundred parts of the stalks of wheat 

 vield l.")-.") pans of ashes (H.Davy)', the same 

 quantity of the dry stalks of barley, 8-54 parts 

 (Srhrader} ; and one hundred parts of the 

 stalks of oats, only 4-42; the ashes of all 

 these are of the same composition. 



" \Ve have in these facts a clear proof of 



what plants require for their growth. Upon 



e field, which will yield only one har- 



vest of wheat, two crops of barley and three 



of oats may be raised. 



" All plants of the -rass kind require silicate 

 of potash. Now this is conveyed to the soil, 

 or rendered soluble in it by the irrigation of 

 meadows. The etjuisefucefn, the reeds and 

 species of cane, for example, which contain 

 such large quantities of siliceous earth, or sili- 

 cate of potash, thrive luxuriantly in marshes, 

 in argillaceous soils, and in ditches, streamlets, 

 and other places, where the change of water 

 renews constantly the supply of dissolved 

 silica. The amount of silicate of potash re- 

 moved from a meadow, in the form of hay, is 

 very considerable. We need only call to mind 

 the melted vitreous mass found on a meadow 

 between Manheim and Heidelberg after a 

 thunder-storm. This mass was at first sup- 

 posed to be a meteor, but was found on exami- 

 nation (by Gmelin") to consist of silicate of 

 potash ; a flash of lightning had struck a 

 stack of hay, and nothing was found in its 

 place except the melted ashes of the hay. 



" Potash is not the only substance necessary 

 for the existence of most plants, indeed it has 

 been already shown that the potash may be 

 replaced, in many cases by soda, magnesia, 

 or lime ; but other substances, besides alkalies, 

 are required to sustain the life of plants. 



The soil in which plants grow furnishes 

 them with phosphoric acid, and they in turn 

 yield it to animals, to be used in the formation 

 of their bones, and of those constituents of the 

 brain which contain phosphorus. Much more 



* After the great fire in London, la'rge quantities of the 

 Erysimum latifoliumwere observed growing on the spots 

 where a fire had taken place. On a similar occasion, the 

 Blitum capitatum was seen at Copenhagen, the Senecia 

 viscosus in Nassau, and the Spartium scoparium in Lan- 

 eruedoc. After the burnings of forests of pines in North 

 America poplars grew on the same soil. (Franklin.) 

 F 2; 65 



