140 MIXED MANURES AND CALCIUM COMPOUNDS 



ammonium oxalate solution in excess. The mixture 

 is boiled for a few minutes and the precipitated calcium 

 oxalate filtered off, washed, dried, and ignited with 

 the filter paper, gently at first and then for fifteen 

 minutes over the blowpipe to CaO. The percentage 

 of lime is calculated as CaS04. 



CaO X 2-428 = CaS04. 



CHAPTER XIV 



Mixed Manures and Calcium Compounds 



Mixed Manures. 



Mixed manures, containing two or more of the chief fertilising 

 constituents, may be natural products or artificial mixtures. Of 

 the former class the most important are the bone manures 

 (nitrogen and phosphoric acid), which have already been discussed 

 (110, p. 127), fish meals and guanos, true guanos, and the sewage 

 products known as Native Guano, British Guano, etc., which 

 may contain nitrogen, phosphates, and potash. 



Guano. 



Three principal types of guano are placed on the market. 

 They include ordinary Peruvian Guano^ which is largely decayed, 

 and has an average nitrogen content of 5 to 8 per cent., largely 

 derived from uric acid ; Ichaboe Guano^ which is very fresh and 

 contains many undecomposed feathers, etc. ; and Phosphaiic 

 Guano^ of the Lobos type, which may contain as much as 60 

 per cent, of calcium phosphate and only 2 or 3 per cent, of 

 nitrogen. 



132. Qualitative Examination of Guanos, 



(a) Peruvian Guano. 



(i) Colour — grey in richer samples; brown in 

 more phosphatic samples. 



