MANUAL FOR SUGAB 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 



