148 CHEMICAL MANUEES. 



nine parts of potash salts with 2-05 per cent of free magnesia 



2 X 0'5 X 29 



(percentage controlled by estimation), the -^ = 0"59 part 



MgO suffices to combine 0*59 x 3*55 = 2 parts of phosphoric acid ; 

 as an actual fact, only 1'4 of insoluble was obtained, which proves 

 that the magnesia did not exert all its action. The cause lies in 

 the slight solubility of magnesia, and in the fact that the salts of 

 potash combine partially with the precipitate formed, so that a part 

 of the phosphoric acid of this latter remains in solution. 



Nitrophos-phate. — The use of nitrate of soda in compound 

 manures is rather restricted ; it is used in making nitroiDhosphate, 

 sometimes in nitrophosijhate of ammonia. It is found that nitrate 

 of soda and sulphate of ammonia are incompatible, and that in 

 fact it is better to use these manures separately. Besides, mixtuies 

 of superphosphate and nitrate sometimes enter into spontaneous 

 combustion in the bags.^ The mixtures of superphosphate and 

 nitrate must be dry mixing. They are no longer objects of tenor 

 to the manufacturer, provided that the superphosphate used has 

 been properly made, for dry nitrate of high percentage mixed with 

 a superphosphate, likewise dry, does not give off nitric acid and 

 cause loss of nitrogen as was often the case formerly when supei- 

 phosphates were wet and the nitrates charged with chloride of 

 sodium. The sodium chloride decomposed by the free phosphoric 

 acid caused the bags to burst in transit, for there is no substance 

 which rots bags like free chlorine and fluorine, two elements given 

 off when nitrate and damp superphosphates are mixed. 



Finally, a manure is made for meadows by mixing kainit with 

 superphosphate or with basic slag."^ The mixing entails no difficulty. 

 The ingredients are mixed with a shovel, then the heap is turned 

 over, the product perhaps passed immediately to the centrifugal 

 crusher, then to the sifting machine. If the kainit be in blocks or 

 lumps it must be passed to the crusher to reduce it to the desired 

 fineness. 



It has already been remarked that in the case of the super- 

 phosj^hate of ammonia of high strength, the phosjjhoric acid soluble 

 in water did not retrograde even when the superphosphate entering 



1 When manure containing nitrate takes fire spontaneously in the bags it 

 is not a case of clamp or wet superphosphate, nor is it a case of impure nitrate ; 

 but it is due wholly and solely to the superphosphate fresh from the mixing 

 " den " being mixed with the nitrate and bagged up before it has had time to 

 cool. Cold superphosphate, however damp, does not act on nitrate of soda, 

 unless in very warm weather. — Te. 



- Kainit long in stock is generally so damp that it blocks and chokes up 

 the crusher. The only way to grind it is by hand labour, by the aid of wooden 

 mallets with long arms, and it is altogether a costly piece of work. Kainit 

 should not be stored in sacks but in bulk on a concrete Hoor where the water 

 can drain away from it. — Tr.. 



