MANUFACTUEE OF BONE SUPEEPHOSPHATE. 185 



an anhydrous state, it is necessary after having refined it to heat it 

 up to 150° C, and to maintain it for some time at that temperatm-e. 

 But it easily finds a buyer even when it contains a httle water. 



Manufacture of Bone Dust. — Fat extracted non-degelatinized 

 bones are reduced to powder which passes through a No. 50 sieve 

 and dispatched to farmers without other treatment. If on the 

 contrary the bones have been deprived of the greater part of their 

 nitrogen, they decompose with difficulty in the soil, and it is better 

 to convert them into super^^hosphates. The crushers used being 

 the same in both cases, the reader is referred to the description 

 already given. The mode of action in the soil of the non-degela- 

 tinized bone dust is based in the first instance in the solubility of 

 phosphate of lime in putrefying gelatine. It behaves in a certain 

 sense like raw Peruvian guano, which has been described, and in 

 which the basic phosphate of lime is rendered soluble by the nitro- 

 genous elements which accompany it. The bone dust in the soil 

 is distinguished by this peculiarity, that its phosphoric acid is not 

 absorbed by the soil, and it can thus penetrate into the deeper layers, 

 whilst every other solution of phosphoric acid is retained by the sur- 

 face soil. This property of bone dust is sometimes of great benefit to 

 the farmer. The return in the same soil during several successive 

 years of plants with a tap root, may have exhausted the subsoil of 

 phosphoric acid. In that case bone dust furnishes the means of re- 

 storing to it new stocks of that element so necessary to vegetation. 

 The finer the bone dust the more easy is it dissolved and decomposed. 

 Coarse powder only acts feebly, but its action makes itself felt for 

 several years. The fine powder decomposes rapidly in the soil and 

 acts energetically the first year. That is why farmers always re- 

 quire a fine powder. It is to the interest of the manufacturer to please 

 them by looking after the crushing and the grinding of the powder. 

 Bone dust made from fat extracted bones has the following com- 

 position, according to Holdefleiss : — 



TABLE L.— ANALYSIS OF BONE DUST FROM FAT EXTRACTED BONES. 



Stored and fat extracted bone dust does not contain more than 

 :2 to 3 per cent of fat. 



