MANUAL FOR SUGAR GROWERS. 91 



to obtain a perfect scum it is necessary to leave 

 the liquid undisturbed so that the minute bubbles 

 of air do not become detached from the solid par- 

 ticles. 



When the temperature is about five degrees below 

 boiling-point it will be found that the liquid is almost 

 clear, all the floating matter having been carried to 

 the surface as scum. This is the point known as the 

 "cracking point" by the work-people, as at this 

 point the dark upper scum tends to crack and dis- 

 play a white frothy scum beneath. The juice is now 

 ready to be drawn off : if this is done with care, the 

 greater part of the juice can be drawn off clear, leav- 

 ing a thick scum behind in the clarifiers ; this scum 

 is drawn off into another vessel, to be treated as de- 

 scribed below. 



On estates where rum is made, the scum is con- 

 veyed to the distillery and is used in setting up 

 the wash for fermentation : many estates, however, 

 from various reasons, have ceased to make rum, and 

 on these it is desirable to extract as much sugar as 

 possible from the scum; this is done by two 

 methods. The first consists in accumulating all the 

 scum obtained in a day's working in a steam-heated 

 vessel termed a defecator or scum-heater, and the 

 clear juice is run off from time to time. By keeping 

 the scum until the following morning a considerable 

 quantity of juice can be recovered, the residue af- 

 ter this treatment usually in practice amounting to 

 four per cent, of the volume of the juice obtained 

 from the mill. 



In the second method the scum is submitted to 



