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2. These are dependent on the chemical, as well as on the 

 mechanical changes, both produced upon burning clay. 



3. Clay after burning becomes more soluble in dilute acids. 



4. The temperature used in burning clay regulates the solubility 

 of clay ; too intense a heat renders clay, again, less soluble. 



5. A temperature whereby the organic matter in clay soils is 

 merely changed, but not destroyed altogether, should be employed 

 in burning clay in the field. 



6. On everburning, clay becomes less soluble than it is in its 

 natural state. 



7. Burnt clay contains more soluble potash f and soda than 

 unburnt. 



8. Properly burnt clay furnishes a larger proportion of soluble 

 potash and soda than clay burnt at too high a temperature. 



9. In burning clay the same effects are produced as in bare- 

 fallow. 



10. The fertilising effects of burnt clay are mainly dependent 

 on the larger amount of potash and soda, particularly of potash, 

 which is liberated from the insoluble silicates in the process of 

 burning. 



11. Clays originally containing much undecomposed silicates of 

 potash and soda are best suited for burning. 



12. On the contrary, those resembling in composition pure pipe 

 and porcelain clays, and all those which contain mere traces of 

 undecomposed alkaline silicates, are unfit for burning. 



13. It is desirable that clay which is intended to be burnt 

 should contain lime. 



14. The application of quicklime to newly burnt clay land, or 

 the mixing of clay with lime before burning, is likely to be 

 attended with much benefit. 



15. Burnt clay absorbs ammonia from the atmosphere. 



16. Clay in its natural state furnishes more ammonia than 

 properly burned clay. 



17. Overburnt clay does not absorb so much ammonia as 

 properly burnt clay. 



18. The causes of the failures attending over-burning, are due : 



1. To the mechanical changes which clay experiences in 

 everburning, whereby it is rendered hard like stone. 



2. To the chemical changes whereby the constituents of 

 clay are rendered less soluble. 



3. To the diminished porosity, and consequently reduced 

 absorptive power of such clays. 



19. Burnt clay improves especially turnips, carrots, potatoes, 

 and other green crops, because it furnishes potash, which these 

 crops largely require, more abundantly and more readily than 

 unburnt clay. 



