THE USE OF MANURES. 6 1 



lined with thick sheet-lead the lead in one piece, 

 soldered at the corners strongly with lead solder. 

 Its capacity is just right for making one-fourth of a 

 ton of superphosphate at a time, and it requires a 

 whole carboy of vitriol, so that no fractional parts 

 of acid are left to cause trouble. It requires : 



One carboy of oil of vitriol 165 pounds 



Bone-charcoal 380 " 



Water 10 gallons 



" The water is first placed in the trough, and the 

 acid is added to it gradually, causing a great boiling, 

 with evolution of heat and steam. It takes about an 

 hour for the reaction to become complete, and then 

 it will soon dry and be free from moisture. It needs 

 no grinding, it is ready for the field as soon as 

 cool." 



136. Guano, one of the most costly and valuable 

 of fertilizers, was in use by the inhabitants of South 

 America, when the Spaniards under Pizarro overran 

 and subdued the powerful empire of the Incas. Pres- 

 cott, in his history of " The Conquest of Peru," gives 

 an interesting account of the progress made in agri- 

 culture by the aborigines of that country. In some 

 places where the dry sandy plains were unproduc- 

 tive, they sank immense pits, some of which were an 

 acre or more in extent, and dug out to a depth of 

 fifteen or twenty feet, in order that moisture suffi- 

 cient for vegetation might be afforded. Other con- 

 ditions of fertility were supplied by thorough pul- 



