Observations on Liehig^s " Organic Chemistry." 123 



to the depth of 20 in., which he estimates at from 300,000 lb. 

 in loam, to 1,152,000 113. in feldspar; and that a single cubic 

 foot of feldspar would supply potash to an acre of pines for 

 five years; deducing hence the absurdity of supposing that 

 plants would generate potash for themselves, when it is so 

 plentifully formed in nature. Argillaceous earths, he says, yield 

 the most potash, the chalk and sand are necessary to keep them 

 open, and give free access to air and moisture. The soil which 

 is formed by the disintegration of lava cannot possibly contain 

 vegetable matter, and the luxuriance of plants on the lava of 

 Vesuvius, after being a few years exposed to the weather, shows 

 the benefit of the alkalies : these soils are more or less fertile, 

 he says, according to the proportion of clay or sand which they 

 contain. The alkalies, he says, are greatly needed in the 

 germination of seeds and young plants ; the acetic acid formed 

 and excreted in the expulsion of oxygen gas, and reduction of 

 the starch to mucilage, is neutralised by the lime, magnesia, and 

 other alkalies, and again absorbed as a neutral salt by the fibres. 

 I formerly pointed out the benefit of alkalies in germination ; 

 when there is much starch and little albumen or gluten in the 

 seed, nitrogen should help ; putrid urine would do, but the 

 quicklime, if used, would decompose the salts of ammonia, and 

 nitrate of potash (saltpeti'e) would be best. He quotes the 

 experiments of Struve, to show how water containing carbonic 

 acid decomposes rocks containing alkalies. Plants also, he says, 

 produce acids by their decay and excrement; thus the disinte- 

 gration of rocks proceeds ; and soils, even though exhausted, 

 will, by rest, again produce alkalies. Around Naples, he says, 

 corn has been cultivated for thousands of years, by allowing two 

 years as fallow, or as a sparing pasture to cattle, which can add 

 no alkalies. The harvests of wheat and tobacco have exhausted 

 the soil of Virginia of alkalies ; 1,200 lb. of alkalies are taken 

 from an acre every 100 years in these crops, and now the land 

 is unfertile. The exhaustion of alkalies, he concludes, is the 

 sole source of want of fertility in soils. Wheat will not grow in 

 the Brazils, he says, though the soil abounds in humus; nor will 

 it grow in Europe in vegetable soils, because the silicate of potash 

 necessary to strengthen the stalk is wanting, and the phosphate 

 of magnesia for the seeds, neither of which substances a soil of 

 humus can afford ; and wheat grows best on clayey soils, because 

 alkalies are contained there in most abundance. Is it accident, 

 he says, that only firs grow in the sandstone and limestone of 

 the Carpathian Mountains; whilst other trees are confined to the 

 gneiss, mica slate, and granite soils of Bavaria, the clinkstone of 

 the Rhone, the basalt of Vogelsberg, and clay slate of the Rhine 

 and Eifeld; the leaves of these trees are renewed annually, whilst 

 the evergreen pine leaves last much longer, and contain fewer 



