OF ARTIFICIAL MANURES. 



165 



4. Salts of potash : — 1 lb. = 2d. The potash or 

 potash salts met with in commerce are, perhaps, 

 nearly three times as dear as here represented ; but 

 in this case considerable expenses are incurred in 

 manufacture and purification, which the farmer must 

 not, of course, include in his reckoning, inasmuch 

 as crude wood-ashes, by which the above price was 

 determined, possess for his purposes the same, and 

 indeed a still higher value, than a corresponding 

 quantity of a purified salt (for instance, carbonate or 

 sulphate of potash). It is fortunate for agriculture, 

 that the cheaper carbonate of soda may in very 

 many cases, in ordinary life, be substituted for the 

 carbonate of potash ; since from this circumstance 

 wood-ashes remain at the service of the farmer. 

 Nevertheless, the important problem of discovering 

 other sources for procuring potash salts than those 

 already known, is still to be solved by agricultural 

 chemistry. Many minerals and rocks contain pot- 

 ash in considerable quantities, and all that is ne- 

 cessary is a simple method by which it may be 

 rendered soluble, and so capable of contributing to 

 the nourishment of plants. If, in a chemical analysis, 

 potash is exhibited as such (that is, not as a salt), 

 one pound may be taxed at Zd. 



5. Salts of soda: — lVo. = l\d. This price has 

 been derived from that of crude common salt and 

 manuring salts. Were the salt-tax removed, this es- 

 timate might be further and materially reduced. 



6. Phosphate of lime (bone-earth) : — lib. = ljc?. 



