190 CHEMICAL MANUEES. 



2 per cent after its conversion into superphosphate. It is small 

 compared with the 15 to 17 per cent of soluble phosphoric acid 

 which accompanies it. Manure manufacturers, therefore, try to in- 

 crease the percentage of nitrogen by the addition of substances of 

 animal origin.^ By this means the enormous amount of daily 

 waste from animal sources in large towns can be restored to the 

 soil. The process is as follows : The bones, as they come from the 

 digesters, are mixed still moist with acid of 50° B., and the nitrogenous 

 matter added. These nitrogenous matters are those already studied, 

 but their treatment differs a little from that applied to them when 

 used alone. 



Blood. — After coagulating the blood by heat in the manner 

 described further on, it is added to the bone dust in the propordon 

 of 300 lb. of fresh blood to 250 lb. of fresh bones. The bone 

 superphosphate thus obtained is rich in nitrogen, it contains in the 

 dry state •! tj 5 per cent of nitrogen, and 9 to 11 per cent of phos- 

 phoric acid ; it only contains 0'51 per cent of insoluble phosphoric 

 acid. The bone superphosphate to which blood has been added, 

 ■dries much better' ; this latter therefore furnishes a means of obtain- 

 ing a perfectly soluble powder richer in nitrogen. If it be desired to 

 still further increase the nitrogen and to bring it to 5 to 6 per cent 

 for example, the difference can be got over by an addition of dried 

 blood, meat meal, or an ammoniacal salt."^ 



Horn. — Although horn previously steamed may be easily crushed 

 in the flatstone mill, it is better to add it in the state of flour to 

 the finished superphosphate, because if added before grinding it does 

 not distribute itself so well as blood. Wool dust and analogous 

 waste are preferably treated like leather waste, for they are too bulky 

 to be treated b}^ steam. 



Leather Waste. — It has already been observed that ground 

 leather prepared from tanned leather is one of the least active of 

 nitrogenous manures. They are best treated as follows : The 

 leather is charged into a large leaden pan capable of being heated 

 by a double bottom or by a lead coil, and moistened with sulphuric 



^But in Great Britain the manure then ceases by law to be dissolved hones 

 and enters the chiss of dissolved bone compo2inds, and in this latter class the 

 units of nitrogen and phosphoric acid are paid for at a much lower rate 

 than in pare dissolved bones. From a manufacturer's point of view, therefore, 

 it is better to use these nitrogenous adjuncts in making dissolved bone com- 

 pounds in which little or no bones are used, the bulk if not all of the phosphates 

 bsing derived from mineral sources. — Tr. 



- But here again the addition of so much blood would cause this manure 

 in Great Britain to fall into the class of blood manures ; at any rate a 

 manure with only 9 to 11 per cent of phosphoric acid (say 20 per cent of 

 soluble phosphates), and no insoluble phosphates, would never pass muster as 

 a genuine dissolved bone. All these animal substances the British manufacturer 

 combines with mineral superphosphate and sells as dissolved bone compound, 

 •or in this case possibly as blood manure. — Tit. 



