io8 CHEMICAL FERTILIZERS 



placed in a circular pressing cage, and the use of boxes is 

 thus entirely dispensed with. Where the cake is intended 

 to be exclusively used for fertilizing purposes, the method 

 of extracting by solvents is frequently employed since a 

 much greater quantity of oil is then obtained. As a rule, 

 petroleum naphtha boiling below 120 C. (248 F.) is 

 used. Carbon di-sulphide and di-chlorethylene can also be 

 used for this purpose, but at the present time petroleum 

 naphtha, frequently called benzine, is preferred. The chlorine 

 derivatives are, however, advantageous, since they are not 

 inflammable. These chlorine derivatives are not altogether 

 advisable for the purpose of extracting cakes suitable for 

 feeding, but for manurial purposes there is no objection to 

 their use. Where solvents are employed, a coarser meal is 

 used than where an oil press is worked. The temperature 

 of extraction will make a considerable difference in the 

 colour of the oil, and therefore cold extraction is often 

 employed. Where the seeds and nuts are in a damp 

 condition, it may be desirable to drive a little benzine 

 vapour through to remove some of the water previous to 

 extraction. The solution is then transferred to a steam- 

 heated still, and the solvent driven off. The last remnants of 

 volatile solvents in the oil are driven out by a current of 

 steam. Sometimes a combination of processes is adopted, 

 whereby a high quality oil is obtained by low temperature 

 pressing, and the residual material is then extracted for the 

 purpose of obtaining a second grade oil, leaving a cake 

 suitable for fertilizers. Among the special cakes used 

 almost exclusively for manurial purposes the following 

 may be mentioned : 



Castor Cake. Castor is pressed very largely in India 

 for the purpose of making burning oil, which is much pre- 

 ferred locally to paraffin. Castor oil is also much used for 

 lubricating purposes, especially for high-speed internal 

 combustion engines. There are many different methods of 

 pressing the oil from this seed. It has been crushed in a 

 screw press, and the pulp put into boxes. About 37 % of 

 cake and 27 % of husk is obtained by this simple process. 



