PLANT AND ANIMAL REFUSE AS MANURE 73 



first were merely ground up and sold as in., J in., etc., bones. 

 This method of employing fertilizers was a very crude one, 

 as the fat in bones hinders their decomposition in the soil. 

 The ordinary commerical bones supplied to bone factories 

 contain 10 % of moisture, 10 % of fat, 18 % of nitrogenous 

 matter, 44 % of phosphate of lime, 5 % of carbonate of 

 lime, traces of phosphate of magnesia, soda, fluorine and 

 chlorine. Where bones must be stored, it is desirable to 

 sprinkle them with a little water containing carbolic acid 

 or other convenient preservative. The chief sources of bones 

 available for manurial purposes are the waste from kitchens, 

 consisting of bones of the ox and sheep, together with horse 

 bones from knackers' yards. In the condition in which 

 bones are collected, they frequently contain 25 % of water. 

 Horse bones are usually separated, because they produce a 

 less valuable glue than the others. Bones of animals, which 

 have been buried, have undergone some degree of decompo- 

 sition, and have lost the whole of their flesh; these are 

 dangerous things to deal with, as they may have come from 

 animals which have died of infectious diseases and have 

 been buried on that account. The bones, having been sorted, 

 if necessary, and having arrived at the factory, are generally 

 passed through a crusher or mill for the purpose of reducing 

 them to a convenient size of about i-in. pieces. It some- 

 times is necessary to use an electro-magnet to separate 

 particles of iron from the bones. Should any sand, chalk, 

 or earth be mixed with the bones in undesirable amounts, 

 some kind of fine riddle will be necessary to separate this 

 impurity from the bones. The crushed bones are placed in 

 an extractor, which often consists of a vertical, cylindrical 

 vessel, to which crude petroleum spirit, commonly called 

 benzine, is added. The benzine is boiled by means of a 

 closed steam coil placed in the bottom of the vessel. The 

 benzine vapour carries away with it a considerable quantity 

 of water contained in the bones. The benzine and water 

 vapours pass away into a condenser, from which they flow 

 in the liquid form into a separator tank. The separator 

 tank possesses a glass gauge, which shows the dividing line 



