180 CHEMICAL MANUEES. 



But this preference is not justified, for bone dust from steam- 

 extracted bones is less rich in nitrogen. The extraction of bones 

 by solvents (benzene, petroleum, ether) gives a larger yield in tallow 

 whilst preserving integrally the ossein of the bones ; these then form 

 a powder rich in nitrogen. This process is undoubtedly to be pre- 

 ferred whatever may be the point of view at which it is looked 

 (manufacture of gelatine, or manufacture of manure). It is the only 

 rational process to apply. 



Extraction of Fat from Bones by Water. — This process is the 

 most ancient, and recalls the skimming of the cook's " stock " pot. 

 In a cylindrical cast-iron pan a little wider below than above, there 

 is introduced by means of a crane a basket of perforated wrought- 

 iron containing about one-half ton of bones. The bottom of this 

 basket, likewise perforated, can open into two semi-circular parts 

 held by hinges on a cross bar, dividing the basket into two equal 

 parts. ' These two doors are closed by hooks, so as to receive the 

 charge. The basket is cylindrical, a little smaller in diameter than 

 the pan which contains it, and shorter by 4 inches. A strong 

 circular hoop at the top supports the sheet iron, and carries four 

 strong handles, by means of which the cross-piece of the crane can 

 lift it. The cast-iron pan is fitted with a gutter or throat, so as to 

 separate the fat from the water in a continuous manner. The 

 basket, therefore, being charged with bones in the fat extraction pan, 

 water is run in to immerse the bones and steam caused to bubble 

 in the bottom from a perforated steam coil. The water, brought to 

 about 100^ C. (212° F.), causes the fat to rise from the bones 

 through holes in the gutter at the same time as the excess of water. 

 The fat flows constantly from the gutter by the horizontal exit tube, 

 whilst the water in the bottom issues through a bent tube without 

 taking any fat with it. The exit of the fat may be facilitated by 

 a superficial push, or by a paddle driven mechanically, mounted 

 on a vertical shaft fixed on the side of the pan, capable of being 

 rotated and raised at the end of the operation, so as to allow the 

 basket to be freely removed from the pan. The bones are extracted 

 in this way for about an hour and a half, after which they are re- 

 moved from the basket to the washer. Certain factories slightly 

 acidulate the water by an addition of sulphuric acid, 4 litres for 

 500 kg. of bones (say 1 gallon for ^ ton), so as to free the grease 

 from its calcareous compounds. There is obtained 1 to 5 per cent 

 of fat according to the quality of the bones. The same water can 



grievous complaint, and he was right too, because boiling removes ammonia. 

 Bones, the fat of which is extracted by petroleum spirit, are possibly not depreci- 

 ated in value to the farmer. The author seems to have written this chapter 

 more from the point of view of the glue manufacturer than the maker of arti- 

 ficial manures. The farmer who knows his business will not take ground steamed 

 bones when he wants ground kitchen or rag bones. — Tr. 



