248 ANNUAL OF SCIENTIFIC DISCOVERY. 



never be improved by burning. The ordinary clay soils, however, 

 contain besides this chief ingredient, a considerable proportion of 

 sand, undecomposed fragments of felspar, mica, granite, and other 

 minerals, with more or less sand, carbonate of lime, magnesia, free or 

 uncombined alumina, oxide of iron, silicate of potash, traces of phos- 

 phorus, and sulphuric acid, and chlorine. Now of these substances, 

 the silicate of alumina, pure clay, does not of itself contribute at all 

 to the direct nurture of plants, as it is not found in the ashes of culti- 

 vated plants. We must look, therefore, for the direct fertilizers of 

 this soil, amongst the accessory or foreign ingredients of agricultural 

 clays. Of these, the lime, magnesia, sulphuric acid, silica, and chlo- 

 rine, which are essential to the growth of plants, are found in most 

 soils, or if deficient, can be supplied at a cheap rate. The chief value 

 of an agricultural clay, depends, therefore, on the proportion of phos- 

 phoric acid, potash, and soda it contains. Potash is a most essential 

 element, and its chief source in ordinary soils is the clay. Clay is in 

 many cases, derived from felspar, a double silicate of alumina and 

 potash; and frequently contains some undecomposed fragments of 

 felspar and other minerals. Plants can only avail themselves of the 

 soluble potash, and not that which occurs in the form of felspar, which 

 must first be decomposed by long exposure to air and water ; but, as 

 the soluble potash in the clay soil, sooner or later, will be exhausted 

 by the removal of the crops grown upon it, the soil becomes gradually 

 more and more sterile. Although by long exposure felspar may be 

 decomposed, yet it is now demonstrated that moderate calcination much 

 accelerates this action. In burning clay properly, a large amount of 

 potash is liberated by the action of the carbonate of lime present, 

 upon the double silicate of potash and alumina. This chemical reac- 

 tion, which occurs at a high temperature, results in the formation of 

 silicate of lime, and carbonate of potash. Those clays, then, which 

 are improved by burning, must be the ones that contain the foreign 

 ingredients named, and undecomposed felspar. The pure pipe and 

 porcelain clays, would not be improved at all, by the process of soil 

 burning. 



We can now understand, why burnt clays, especially improve the 

 root crops, such as turnips, carrots, swedes, mangolds, potatoes, &c., 

 which require much potash as nutriment, the ashes of these plants, 

 containing nearly half their weight of this alkali. 



ON THE ABSOKPTION OF THE SOLUBLE IIUMATES AND ULMATES 



BY PLANTS. 



M. SOUBEIRAN demonstrated some time since the important fact, so 

 long denied by Liebig and his supporters, that alkaline ulniates and 

 humates are absorbed by vegetation. The experiments of Soubeiran 

 have been recently verified in the fullest extent by M. Malguti. 



A plant of Lampsana, whose roots were immersed in a solution of 

 ammonia, continued to vegetate and prosper. The solution, which 

 was changed every day, was partially discolored. Oats passed very 



