THE ALKALIES. 51 



in the nature of the matters expelled is effected by their exposure to 

 the air in the process of cultivation. The nature of the soil also 

 greatly contributes to hasten or retard this change. Flax, peas, clover 

 and potatoes require the longest time in argillaceous soils, for the mod- 

 ification of the matter they expel ; but the use of alkalies and burnt 

 lime effects this in a much shorter time ; so that the artificial use of 

 certain substances will speedily effect what would require a long time 

 by the unaided processes of nature. This change is supposed to be 

 the conversion of the expelled matter into humus. The inundation of 

 fields or meadows is admirably calculated, oftentimes, to accomplish 

 this change. 



Ml plants require alkalies, the grains especially in the form of sili- 

 cates ; that is, silicic acid combined with an alkali ; others require 

 tartrates, citrates, acetrates, or oxalates, which are also salts formed by 

 the union of an acid, i. e., tartaric acid, acetic acid, or vinegar, oxalic 

 acid, etc., with alkaline bases. The alkalies are potash, soda, ammo- 

 nia, lithia, etc. ; the 1st is a vegetable, the 2d a mineral, and the 3d a 

 volatile alkali. Lime, magnesia, baryta and struntian are called alka- 

 line earths. Morphia and quinia are alkalies or alkaloids : all form salts 

 with the acids in the same manner as common salt, which is a union of 

 muriatic acid and the alkali soda. Silica is an earth in the form of 

 sand, flint, quartz etc., and is most abundant. The woody parts of 

 plants, and the stalks of grains, reeds, etc., have much of it. Silicic 

 acid is the first form taken up by plants for the formation of the wood. 

 Some plants require phosphate of lime, some phosphate of magnesia, 

 and others carbonate of lime. Some require very little of these inorganic 

 matters, as sanfoin, lucern, etc. ; these spread wide their roots, and 

 are much used now to alternate crops. When soil is manured 

 once in nine years, turnips are first sown, next barley, with sanfoin, 

 or lucern for five or six years, then potatoes, then wheat, then barley ; 

 and then it is manured and the same crops follow. The importance of 

 spreading light silicious soils with ashes of wood and bones for the 

 purpose of furnishing alkalies, especially phosphates are well known. 

 The ashes of oak are least and those of beech most valuable. Bones 

 afford 10 times more than either. A time will come, says a distin- 

 guished chemist when fields will be manured with a solution of glass 

 (silicate of potash) with the ashes of burnt straw, and with salts of 

 phosphoric acid, prepared in chemical manufactories, exactly as medi- 

 cines are given for fever, etc. 



The most important object in cultivating plants is the production of 

 nitrogen in a form for its assimilation by them. The roots, from 

 which the leaves are formed, and the leaves which nourish the woody 

 parts and prepare substances for the composition of the fruit, and also 

 the seeds, abound with it. This is furnished mainly by the atmos- 

 phere, as we have said, and plants convert all of it into nutriment 



