PHOSPHATE FERTILIZERS l8l 



the product is sometimes called Thomas' slag. At the 

 present time but little basic slag is produced for fer- 

 tilizer purposes in this country. In Germany and 

 some other European countries the amount used is 

 nearly equal to the amount of superphosphate. Phos- 

 phate slag is ground to a fine powder and is applied 

 directly to the land, without undergoing the sulphuric 

 acid treatment. Phosphoric acid is present mainly in 

 the form of tetracalcium phosphate, (CaO) P 2 0_. 



220. Guano is the Spanish for dung, and is a concen- 

 trated form of nitrogenous and phosphate manure of 

 interest mainly on account of its historic significance. 

 It is a mixture of sea-fowl droppings which have ac- 

 cumulated along the seacoast in sheltered regions. 

 The mixture of dung, dead animals, and debris, has 

 undergone fermentation, and is concentrated in both 

 nitrogen and phosphoric acid. The introduction of 

 guano into Europe marked an important period in agri- 

 culture, inasmuch as its use demonstrated the action 

 and importance of concentrated fertilizers. All of the 

 best beds of guano have been exhausted and onlv a 

 little of the poorer grades are now found on the mar- 

 ket. The best qualities of guano contained from 12 

 to 15 per cent, of phosphoric acid, 10 to 12 per cent, 

 of nitrogen, and from 5 to 7 per cent, of alkaline salts. 



BONE FERTILIZERS 



221. Raw Bones contain, in addition to phosphate 

 of lime, Ca„(PO ) , organic matter which makes them 



