1012 THE COMPLETE GRAZIER. BOOK xi. 



are not " manure " in the generally accepted sense and are treated of 

 separately (see p. 1024). 



Artificial manures differ in the constituents of food that they supply. 

 Some furnish only one food, such as nitrogen or phosphorus or 

 potassium, while others yield two or more constituents of plant food. 



BONES are used in various forms as manure, but they should always 

 be obtained by preference in as finely ground a state as possible. 

 Coarsely crushed bones are often praised on account of their " lasting " 

 qualities. This merely means that it is a long time before the farmer 

 gets the full return for his outlay. Good raw bone meal contains from 

 about 45 to 50 per cent, of phosphate of lime, and nitrogen equal to 

 from about 4 to 5 per cent of ammonia. Bones that have been highly 

 steamed to remove the gelatine for glue making purposes, yield a good 

 deal more phosphate, but often nitrogen equal to only 1 per cent, of 

 ammonia. Care, therefore, should be exercised in the purchase of 

 bone dust. Bones are essentially a phosphatic manure, but their 

 yield of ammonia on decomposition is, as already intimated, very con- 

 siderable. 



FISH GUANO. The manure thus named consists of fish offal, or 

 sometimes of whole fish, dried and ground up. Like bones, it contains 

 both phosphates and nitrogen, but is much richer in nitrogen than are 

 bones. Fish guanos, according to their source and the materials of 

 which they are made, yield from about 9 to 12 per cent, of ammonia, 

 and from 10 to 15 per cent, (sometimes even 18 per cent.) of phosphate 

 of lime. They often contain fish-oil, which, as it delays decomposition, 

 renders them less serviceable as manures. 



PERUVIAN GUANO consists of the accumulated excrement of sea- 

 birds found in the more or less rainless districts of Peru. Formerly it 

 was an exceedingly concentrated ammoniacal manure, but latterly, as 

 the best deposits have been used up, it has assumed a different character, 

 being richer in phosphates and poorer in nitrogen. 



Genuine Peruvian guano as at present offered varies much in compo- 

 sition. The higher qualities yield 8 to 10 per cent, of ammonia, while 

 the poorer ones give only about 4 per cent., but are very rich in 

 phosphates. The superior qualities are still a favourite manure with 

 many farmers for top dressing corn crops, though the high price and 

 the small supply limit their use a good deal. The lower qualities, 

 rich in phosphates and poor in nitrogen, are cheap and much to be 

 recommended for various purposes in lieu of fine bone-meal, to which 

 they are probably preferable. 



SUPEKPHOSPHATES, DISSOLVED BONES, AND DISSOLVED GUANO. To 



render the action of bones more rapid, Liebig suggested their treatment 

 with sulphuric acid, which converts part of the insoluble tribasic phos- 

 phate of lime they contain into a new compound of phosphoric acid 

 which readily dissolves in water and softens the remainder. The same 



