CHAPTER XYI. 



POTASSIC MANURES. 



Preliminary Remarks. — The ash of plants consists for the most 

 part of carbonate of potash, the caustic and detergent properties of 

 which were bound to attract attention from the very beginning of 

 civihzation. And as a matter of fact the ancients knew this sub- 

 stance and employed it in domestic economy as well as in industry. 

 Aristotle described the manner of extracting potash from the ash 

 of plants. His process is still in use in certain countries. It con- 

 sists in submitting the ash to a series of washings with water, 

 concentrating the lye by evaporation, and in calcining the residual 

 salt. As plants only leave a small amount of ash, and as this does 

 not wholly consist of carbonate of potash, it is clear that the yield 

 of potash cannot be very great. The plants the most rich in potash 

 are the following :— 



TABLE XCIII.— POTASH CONTENT OF VARIOUS PLANTS. 



In this category some plants will be remarked as very rich in potash, 

 such as fumitory, absinth. Did not some persons have the idea about 

 1850 of cultivating them to extract the potash ? Thus, in Sardinia, 

 a plant was cultivated called in common language glacialo (Mesem- 

 bryanthemum cristallineum) so as to obtain potash by burning it. 

 The analvsis of the ash of this plant, cultivated in le Nord, gave 30 



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