PHOSPHATE OF LIME — ASHES. 323 



if too strongly heated, it loses its property of again 

 absorbing water. 



877. Phosphate of lime is found native as a min- 

 eral in Spain and other countries ; it certainly forms 

 a most valuable manure for poor soils. As phos- 

 phate of lime is found in nearly all plants, all sub- 

 stances containing it are useful as manures (732). 

 The native phosphate of lime has, as yet, hardly 

 come into use at all as a manure, in consequence of 

 the expense of collecting and carrying it to any dis- 

 tance. Phosphate of lime exists abundantly in bones 

 (595), and in smaller quantity in all organic ma- 

 nures, and in the ashes of plants. A minute quantity 

 of phosphate of lime is found in many rocks, and in 

 particular kinds of chalk and marl, which are conse- 

 quently valuable additions to the soil. The copro- 

 lites, and other forms of fossil manure which have 

 been so much talked of, of late, contain a considerable 

 quantity of phosphate of lime ; large deposits of these 

 substances exist in various parts of the country. 



878. There are no mineral manures which contain 

 phosphate of magnesia ; it exists in many soils, and 

 in a good many organic manures. Bran contains a 

 considerable quantity of this salt. Magnesia, in its 

 pure and caustic state, appears to be hurtful to 

 plants, but some of its salts are useful ; thus, sul- 

 phate of magnesia, or Epsom salts, has been found a 

 valuable manure for potatoes, &c. 



879. Ashes of all kinds constitute an important 

 class of manures. They are of value for the char- 



