MANUAL FOR SUGAR GROWERS. 93 



A great many filter-presses are on the market, all 

 based on the principles here stated, but varying 

 greatly in the details of their construction. 



When sugar-cane scums are treated in a good 

 filter -press with a pressure of about forty-five 

 pounds per square inch, a very large quantity of 

 juice is recovered, and there remains in the press a 

 solid, nearly dry cake, which in practice is about 

 one per cent, of the volume of the juice obtained 

 from the mill. It is thus seen that a good filter- 

 press efiects a saving over the first method — where- 

 by four per cent, of residual scum is obtained — of 

 three per cent. 



The following analyses of the scum-cake, after 

 drying, will serve to show its general character : 



Composition of Filter-pkess Cake, per 100 Parts. 



Harrison. Watts. 



Moisture 14.76 10.04 



Organic matter* 66.93 68.45 



Silica, sand, etc 3.20 5.40 



Phosphate of lime 12.95 13.36 



Oxide of iron 92 .52 



Alumina . . .08 



Magnesia . , .22 



Potash 12 .15 



Soda .10 



Matter not estimated 1.12 1.68 



100.00 100.00 



* Contains nitrogen 2.07 1.91 



The amount of phosphate of lime in the cake de- 

 pends upon the manner in which the operation of 

 tempering has been conducted. If the juice be un- 



