82 CHEMICAL MANURES. 



Florida phosphate good results are obtained by increasing the 

 theoretical amount by 5 per cent. It is easy to understand, more- 

 over, that the richer the raw material is in phosphoric acid the less 

 it should be over-acidified, because the phosphates of that category 

 generally contain little sesquioxides or silicates capable of absorb- 

 ing the acid added in excess. Phosphates rich in carbonate of lime, 

 such as Somme and Algerian phosphates, stand much acid ; how- 

 ever, the excess of acid rarely surpasses 5 per cent of the quantity 

 calculated according to their percentage of phosphoric acid.^ 



If the trial mixing be well conducted it gives very satisfactory 

 results. The superphosphate obtained should be comparatively 

 dry and porous when it is cold. After each trial the phosphoric 

 acid, soluble in water, is determined, the free phosphoric acid and 

 the insoluble phosphoric acid. Bone phosphates are almost com- 

 pletely rendered soluble. But it is not so with mineral phosphates, 

 which always leave a small amount of insoluble phosphoric acid. 

 This fraction amounts to about 1*4 for Gafsa superphosphate, 1*7 

 for Algerian, 1'4 for Peace River and Pebbles, 0*5 to 1 for Florida, 

 1-7 for Carolina, and 2-1 for Tennessee (Schucht). Up to now the 

 efforts of scientists and practical men have been powerless to 

 abolish this loss. The density and strength of the acid play a 

 <;ertain role in mixing. Phosphates rich in carbonate work best 

 with cold acid, whilst those poor in carbonate require hot acid. It 

 has been found, moreover, that the soluble phosphoric acid is better 

 preserved in superphosphates prepared with acid of 54° B. than in 

 superphosphates made with acid of 60° B. 



Damp phosphates and those difficult to dissolve require stronger 

 acid than when dry and rich in carbonate of lime. 



Finally, it is well to bear in mind that superphosphates should 

 contain a certain amount of free phosphoric acid. That has the 

 effect of retarding the decomposition of the acid phosphate of lime 

 in the soil, and regarded from that point of view it constitutes an 

 indispensable element of the superphosphate. 



Schucht shows in the following table the amount and the 

 strength of acid which it is convenient to use in rendering various 

 phosphates soluble. 



^In the translator's experience with Somme phosphate, 60 to 62 per cent 

 Ca-PaOj,, he found that it invariably took exactly its own weight of sulphuric acid 

 calculated as B.O.V. He preferred to use acid heated to 150° F. Somme 

 phosphate rises much more in the mixing den than Carolina, so that it will hold 

 nearly twice as much Carolina super as it will of Somme super. But great care 

 must be taken that there is no flaw in the closed steam pipe heating the acid, or 

 the acid may gain access to the boiler. The translator had a ease of this sort 

 where the engineer, after ruining his boiler, in order to escape censure, tried to 

 blame his well-water as being naturally acid I — Tr. 



