ARTIFICIAL MANURES AND HORTICULTURAL PRACTICE. 49 



of nitrogen, 201 lbs. of phosphoric acid, and 2 lbs. of potash, 

 with 1,535 lbs. or 68J per cent, of lime. Sample No. 2 had been 

 adulterated with sand, and contained in each ton 13 lbs. of 

 nitrogen, 41 lbs. of phosphoric acid, no potash, and 515 lbs. of 

 lime. About three-quarters of this sample, or 75 per cent., 

 consisted of sand. 



Good Peruvian guano has some advantage over most other 

 unmixed manures containing the same percentages of nitrogen 

 and phosphates, on account of its more complex chemical con- 

 dition, the manurial constituents being in several different forms, 

 of different degrees of solubility, so that they supply the plant 

 requirements more slowly and evenly through the period of 

 growth than can be done by manures in which the contents are 

 each in some one form of chemical combination. 



It has already been mentioned that guanos are found, varying 

 in composition from the most highly nitrogenous, to those con- 

 taining very small percentages of nitrogen, and that, generally 

 speaking, those poor in nitrogen are rich in phosphoric acid. 

 Hence we find that phosphatic guanos are usually obtained from 

 old deposits which are located in rainy districts, and very largely 

 from various islands in the Pacific. The materials left after a 

 long exposure to the weather are chiefly mineral matters, con- 

 taining phosphoric acid and magnesia, together with various 

 impurities. 



These guanos are frequently used for the manufacture of 

 compound manures, and if properly made are rapidly acting 

 fertilisers. 



Phosphatic Manures. 



The next four items in Table V. deal with phosphatic 

 manures. Phosphate of lime is a substance which has acquired 

 considerable importance in recent years, and is a fertiliser of 

 great consequence. There are several varieties of this substance, 

 as the term " phosphate of lime " includes such well-known 

 manures as boned meal, bone ash, bone black, superphosphate of 

 lime, phosphatic rock, basic slag, &c. 



Bones may properly be included under the head of artificial 

 manures, because they are allied to phosphatic guanos, and 

 receive similar treatment in rendering their phosphate contents 

 soluble, as in the preparation of superphosphate. 



E 



