ON MANURES. ]<21 



all organic matter yields hidrogen gas. Phosphorus may be 

 gained from all calcareous earths. 



What venders it particularly valuable is the calcareous Properties, 

 earth it contains. But we do not yet know what ought to 

 be the quantity of calcareous earth in a soil. The best spe- 

 cimen analyzed by Giobert had 6 per cent} by Bergman, 

 30; by Dr. Fordyce, 2; and a rich soil quoted by Mr. 

 Davy had 11. This is an inquiry, concerning which the 

 author has made many experiments, and on soils of the 

 most extraordinary fertility. In one he found 9 per cent; 

 in another 20; in another 3 : arid in a specimen of famous 

 land, procured from Flanders, 17. Many poor soils how- 

 ever possess nearly the same proportion as the most fertile : 

 and on comparing every circumstance he is disposed to con- 

 clude, that the necessity of a large proportion of calcareous 

 earth depends on the deficiency of that organic matter, 

 which is convertible into hidrogen gas. If the farmer find 

 by experiment, that his soil contains but a small quantity 

 of organic matter; or know by his practice, that it is poor, 

 and not worth more than 10, 15, or 20s. an acre ; it ought 

 to have 20 per cent of calcareous earth in it. If on the con- 

 trary it abound with organic matter, and be worth in prac- 

 tice a much larger rent, it will not require marling, though 

 it contains but 3 per cent of calcareous matter, or even less. 

 Maries likewise give tenacity and firmness to a soil, and for 

 this the clay maries are to be preferred. Some soils abound 

 with acid particles, which are prejudicial ; and these are 

 neutralized by the caleareou earth. 



The earth found in vegetables is for the greater part cal- 

 careous. Hence we may presume, that this earth should 

 make a part of the soil. Lord Dundonald calculates, that 

 all the calcareous earth to be obtained from the vegetable 

 produce of an acre of most crops will not exceed eighty 

 po :ncls: but if even this quantity be required for every 

 crop,'the necessity of occasional supply appears. 



Marie is generally obtained by digging, but it is also Collecting, 

 dredged up from the beds of some rivers. White sheil 

 marie, and a very light white species, are found under bogs, 

 and at the bottom of lakes. No person, whose land wants 

 marie, where it is not generally known to exist, should be 



satisfied 



