230 



On Superphosphate of Lime. 



much of it has remained in its original state for want of proper 

 contact, and the result is an inferior manure produced at a cost 

 which should have ensured success. 



For the same reason dilution of the acid to such an extent as 

 it may be fairly carried out consistently with the subsequent 

 drying- up of the product is, in all cases, advisable. A rise of 

 temperature, whenever it can be effected, is of great use; the 

 mere mixture of bones and sulphuric acid will produce much 

 heat, but if the acid has to be diluted the use of boiling water 

 will prove of great assistance ; considerable caution must, how- 

 ever, be employed in the mixing of the water and acid on account 

 of the violence of the action. 



The mode of mixing the materials has also a most material 

 influence on the result. It might reasonably be supposed that a 

 given quantity of acid would ultimately produce the same amount 

 of action, whether it were mixed by degrees or at one time; such 

 however is not the case. At page 217 it was stated that the 

 phosphate of lime of 100 lbs. of bones would be entirely con- 

 verted into bi-phosphate by 44 lbs. of oil of vitriol ; now, supposing 

 that we divided the heap into two portions, adding the whole acid, 

 after proper dilution, to one, and subsequently, when the action 

 had time to take place, mixing in the other heap ; instead of the 

 acid removing just so much lime as would convert the whole phos- 

 phate into bi-phosphate, it would go much further than this, and 

 would thoroughly decompose the bi-phosphate at first formed, 

 all the sulphuric acid becoming neutralized and phosphoric 

 acid being liberated ; but this acid is comparatively a weak acid, 

 and acts very slowly and inefficiently on the remainder of the 

 phosphate. I have found that, though a solution of phosphoric 

 acid readily dissolves sufficient precipitated phosphate of lime to 

 convert it into bi-phosphate, it acts with comparative feebleness on 

 crushed bones, and requires days or weeks to dissolve the mineral 

 phosphates. Nothing, therefore, can be more unsatisfactory 

 than the mixing of bones or other phosphoric substances in large 

 heaps with the acid ; whatever care is subsequently taken to mix 

 them, the action must inevitably be partial and incomplete. The 

 manufacture of superphosphate of lime as a trade should always 

 be carried on with the aid of machinery ; the acid and bones or 

 mineral phosphate should be brought together in their proper 

 proportions little by little, so that the bi-phosphate should be 

 produced at once by abstraction of the lime, and not by a slow and 

 uncertain action of liberated phosphoric acid on further quantities 

 of phosphate of lime. 



The necessary utensils for this purpose need not be compli- 

 cated ; it is only requisite that the powdered phosphoric substance 

 and the dduted acid should be brought together in proper pro- 



