BONE MANURES 175 



mixing and charging, a good dissolved bone can be removed 

 from the den ; by putting it into heaps and occasionally 

 spreading, a very satisfactory dry dissolved bone can be 

 made. Where manufacturers use a weak acid the excess of 

 the water must be driven off, and therefore artificial drying 

 in some way is necessary. Artificial drying ovens with the 

 necessary air ventilation can be obtained, but quite a satis- 

 factory result may be produced by spreading the dissolved 

 bone on a stone floor, heated by flues, and turning it over from 

 time to time. The process of dusting with bone meal, or, 

 better still, steamed bone flour, may be practised in the same 

 way as in the dusting of superphosphate with mineral phos- 

 phate powder, p. 150. By such methods of drying and 

 dusting, the correct dry condition can be obtained that is so 

 necessary for sowing on the field with manure distributors. 

 The difficulty of obtaining a dissolved bone in a fine dry condi- 

 tion is so great, that it is never desirable to make any effort to 

 push the solution as far as it is pushed in the manufacture 

 of mineral superphosphates ; frequently only half the total 

 amount of phosphate present is rendered soluble, and a 

 typical good class dissolved bone should contain 3% of nitro- 

 gen and 15% of phosphates rendered soluble, with 15% of 

 phosphates remaining insoluble. Great variations occur in 

 the composition of dissolved bone, since the bones from which 

 it is made themselves vary, the method of manufacture 

 varies, and the degree to which solution is attempted is also 

 very variable. In some cases manufacturers produce a 

 dissolved bone with more than three-quarters of the total 

 phosphates in a soluble condition ; in this case the remarks 

 which are made on p. 144 with reference to the relation- 

 ships between free phosphoric acid and tri-calcium phosphate 

 will very nearly apply. In other cases, where only half of 

 the phosphates are dissolved, these relationships are no 

 longer true, since the tri-calcium phosphate was not origin- 

 ally completely converted into mono-calcium phosphate, but 

 remained from the beginning to a large extent in the form of 

 di-calcium phosphate. 



The sulphuric acid used produces a marked chemical 



