PHOSPHATES 71 



purposes has been boiled or steamed in the rendering factories 

 to extract the fats and nitrogenous compounds which are used 

 in making soap, glue, and gelatine. The bones are then ground 

 or pulverized and sold as steamed bone-meal, bone-meal and lx)ne- 

 (lust. This product is variable in composition, ranging from 17.5 

 to 29 per cent, of phosphoric acid and 1.5 to 4.5 per cent, of 

 nitrogen. Good clean bone-meal should contain at least 2.5 per 

 cent, of nitrogen and 25 per cent, of phosphoric acid. The 

 treatment of the raw bones affects the final composition of the 

 product (steamed bone-meal) ; the boiling or steaming reduces the 

 nitrogen content and increases the phosphoric acid. 



Steamed bone-meal is a more quickly available fertilizer than 

 raw bone-meal and is therefore better for most crops. 



There is a great difference in the steamed bone-meals put 

 upon the market not only in the composition but in the hardness 

 of the product. Steamed bone-meal from some factories is more 

 porous and softer than from others. Some factories put out a 

 product that crumbles easily while others sell meal that is ex- 

 tremely hard.* 



Degree of Fineness. — The bones when sold for fertilizing pur- 

 ix>ses are ground fine and are known as fine ground bone, bone- 

 meal, bone-dust and bone-flour. The mechanical condition of 

 fineness does not affect the composition but increases the avail- 

 ability of the product for plant food. Hence the finer the bones 

 are ground the more valuable they are as quicker acting fertilizers. 

 These products are generally valued according to their degree of 

 fineness and chemical composition. It must be remembered that 

 all bone-meals give up their plant food slowly and are not de- 

 sirable for immediate results in the production of crops.* 



Bone-Black. — In the manufacture of bone-black, the choicest 

 bones are selected, cleaned and dried. They are then put in air- 

 tight vessels, heated and distilled until all the organic or volatile 

 matter has passed off. The product is then ground to a coarse 

 consistency and sold to the sugar refineries for clarifying or de- 

 colorizing syrups in the manufacture of white table sugar. After 

 it has served its usefulness in the sugar refineries it is sold for 

 6 



