2*6 VEGETABLE SUBSTANCES. 



solid mass ; or, if the heat be very great, into a paste- 

 like substance of a whitish grey or marbled colour. 

 This operation will frequently require twenty or 

 twenty-four hours, and sometimes even more, for its 

 completion, dependent on the purity of the ashes 

 with respect to the proportion of extractive and other 

 extraneous matter which they may contain. Re- 

 course must in this process be had to the chisel and 

 mallet to extricate the potash from the fusing vessel, 

 and therefore no advantage is apparently derived 

 from the fusion of the alkali, while it has the objection 

 (which Kirwan cautions the operator to avoid) of 

 being extremely difficult of solution. Though it 

 soon partially liquifies it does not, unless previously 

 pulverised, readily and wholly dissolve even by 

 boiling in water. 



It is calculated in America that a ton of potash is 

 obtained from four to six hundred bushels of best 

 ashes. The following table, taken from the first 

 Supplement to the Encyclopedia Britannica, will 

 show the relative quantities which different plants 

 contain, as the result of the experiments of some of 

 the most eminent French and English chemists : 



; Ashes. Potass. 



, 100 parts Sallow produce . . .2-8 0-285 



Elm 2-36727 039 



Oak 1-35185 0-15343 



Poplar 1-23476' 0-074SI 



Hornbeam M283 0-1254 



Beech 0-58432 0-14572 



Fir . 0-34133 



Vine branches .... 3'379 0'55 



Common nettle. . . . 10-67186 2-5033 



Common thistle . . . 4-04265 0-53734 



Fern ...... 5-00781 0-6259 



Cow-thistle .... 10-5 1-96603 



Great river rush . . . 3-85395 072234 



