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Oa the Causes of the Efficacy of Burnt Clay. 



atmosphere, is brought up ; and, amongst other changes, the un- 

 decornposed fragments of felspar are forced, by the combined 

 action of air and water, to yield their potash and soda, which are 

 the indispensable requisites of a healthy vegetation. 



In an age of railway and steam enterprise and telegraphic 

 despatch, agriculture is forced to progress, and, in consequence 

 of this, fallowing must necessarily yield to some more extensive 

 and expeditious means of gaining the same advantages. Soil- 

 burning is one of these means. The above-mentioned analvses 

 have taught me that, in burning clay, a large proportion of pot- 

 ash, which existed before in an insoluble state, is liberated and 

 rendered available for immediate use by plants. In burning clay 

 then similar chancres are effected in a few days, which in bare- 

 fallowing are produced in so many months. To this liberated 

 potash I am inclined to ascribe the cliief ejfficacy of burnt clay, 

 without, however, considerins" the mechanical changes clay under- 

 goes in burning as unimportant. 



The fact that felspar is more readilv decomposed after having 

 been moderately calcined is not a new one, Professor Fuchs, of 

 ^Munich, having shown clearly that this is the case not only with 

 felspar, but also with other minerals, into the composition of which 

 silicate of potash enters. Fuliv in accordance with this fact is 

 the practical observation of Professor Lampadius, who found, by a 

 series of field experiments, that moderately calcined gneiss, granite, 

 certain kinds of porphyry and trap rocks, all of which contain 

 silicate of potash in a similar manner as burnt clay, promote the 

 luxuriant growth of many plants in a remarkable manner. 



Phosphoric acid, the only other valuable constituent of agricul- 

 tural clays, is not rendered more soluble by burning, but rather 

 the contrary ; the efhcacy of burnt clay, therefore, cannot be due 

 to phosphoric acid. 



I have shown above in what manner lime appears to me instru- 

 mental in liberating; the potash of clays. If this explanation of 

 the action of lime on silicate of potash is true, v/e can easily con- 

 ceive how the addition of lime to clay, originally poor in this ele- 

 ment, will increase the amount of soluble potash and soda. I 

 would, therefore, suggest the application of quick-lime to newly 

 burnt clay land, or the mixing of clay with lime before burning, 

 as likely to be attended with most beneficial effects. The ex- 

 planation of the action of lime on clay, and the suggestion I have 

 ihrov/n out, are supported by an observation of Professor Fuchs, 

 of Munich, to which particular interest attaches. This distin- 

 guished man found that when felspar is moderately burnt, and in 

 a powdered state is boiled with quick-lime and water for a short 

 time, or even digested in the cold with quick-lime and water for 

 a longer period, so large a proportion of potash is liberated from 



