MANUFACTURE OF BONE SUPERPHOSPHATE. 189 



by means of a steel ball mill, or by a Carr's disintegrator. The 

 powder yielded by the crusher is then passed through a No. oO 

 sieve, and the core returned to the crusher, which finally reduces it 

 to the desired fineness. 



The bone dust is then mixed with the desired amount of dilute 

 sulphuric acid, using the same mixer as in making mineral super- 

 phosphates. But bone dust does not behave nearly so well as 

 mineral phosphate under the action of the sulphuric acid. It 

 has already been pointed out, that mineral superphosphates contain 

 free phosphoric acid, which renders them moist to the touch. To 

 this drawback, another is added in the case of bone superphosphate, 

 the sulphuric acid converts the organic matter into a viscous mass, 

 which prevents the drying of the superphosphate. 



A multitude of methods have been tried to eliminate this draw- 

 back, but the greater number have failed. In this way it has been 

 tried to dry the superphosphate with sand, lignite, ash, and other- 

 analogous pulverulent matters. But the addition of all these sub- 

 stances not only diminishes the percentage of nitrogen, but it opens- 

 the door to sophistication of all sorts. It has been given up. 



Another way of attaining the same object, proposed by Rumpler, 

 was the use of bone black. As this material possesses considerable- 

 absorptive power for liquids, it may be successfully used to dry 

 manures with a tendency to remain damp. The bone black is in- 

 corporated thus: The bone black is first incorporated with the- 

 quantity of sulphuric acid required to dissolve its phosphate, at the 

 same time as that for the bone dust. When the decomposition of the' 

 black is finished, the bone dust is incorporated with the mixture.. 

 If any insoluble phosphate remains undissolved, it is bone phos- 

 phate, which becomes readily soluble in the soil. 



If it be desired to increase the amount of nitrogen, the gelatine 

 extract obtained by steaming bones may be added to it. But, so as 

 not to introduce too much water into the manure, care is taken to 

 reduce its volume to a third by evaporation, and to use sulphuric 

 acid of high strength. Finally, it is preferable to secure the drying 

 of the phosphate bv only dissolving it incompletely. In that case, 

 only f or | of the sulphuric acid required for completely dissolving 

 the phosphate is used. 



Again, the addition of a little nitrate of soda 1 : 2 per cent con- 

 siderably accelerates drying. 



Bone superphosphate dries spontaneously in the heap, and at the* 

 end of a month the reactions of which it is the seat are terminated. 

 It suffices then to pass it through a Carr's crusher, and to sift it 

 to reduce it to a pulverulent form. 



Mixture of Bone Superpliosioliate (Dissolved Bones) and Nitro- 

 genous Matter. — Bone dust from steamed bones only contains on 

 an average 3 to 4 per cent of nitrogen. It does not contain more than 



