ANIMAL MANURES. 133 



amount of combustible matter which they contain, according 

 to the age of the animal, and other circumstances. A bushel 

 usually weighs from 42 lbs. to 45 lbs. Fresh bones, as ap- 

 plied to the land, contain about twenty per cent of water. 

 The following is theu* per-centage composition, when dry: — 



Organic combustible matters, SS^lbs. 



Incombustible matter or ash, consisting of 



Phosphate of lime (bone earth), 55^ 



Phosphate of magnesia, 3 



Carbonate of lime, 3| 



Saltaof Socla, 3^ 



Fluoride of calcium, 1 



100 lbs. 



198. The organic portion of bones consists of oil, and of 

 a jelly-like matter possessing nearly the same composition as 

 horn, skin, and hair. This matter is capable, by its slow 

 decay in the soil, of producing two gases — carbonic acid and 

 ammonia — by means of which, it is considered, that carbon, 

 which we recognise as the chief constituent of wood, starch, 

 &c. (60-64) and, also, nitrogen, the element so indispensable 

 to the formation of the seed, may be supplied to the rootlets 

 of the growing vegetable, and employed for its development. 

 The organic matter of 100 lbs. of bones is capable of yielding 



' about 5^ lbs. of nitrogen. The earthy matter consists chiefly 

 of the phosphates which, as I have repeatedly explained, are 

 of such immense importance to our soils. 



199. JJ^ow do Bones act? — The mode in which bones 

 prove serviceable is yet an unsettled question among scientific 

 agriculturists. Formerly, before chemistry had demonstrated 

 the importance of the inorganic elements of plants, it was 

 generally supposed that all their qualities, as fertilizers, were 

 due to the organic matter which they contained. This opi- 

 nion, however, was considerably shaken by the observations 

 of many farmers, who had employed burnt bones, and the 

 bones which are boiled at Manchester for the manufacture of 

 glue, apparently with equal, and, in some cases, it is reported, 

 with superior effects to those produced by crushed bones. 

 At present, many persons are inclined to attribute all the 

 effects produced to the phosphates which they supply to the 

 exhausted soil. Sprengel, who is a supporter of this opinion, 

 instances their failure in places in the north of Germany, 

 where other animal manures, rich in organic matter, had 



