310 On the Mamifaciwe of Muscovado Sugar. 



The aerlForm bubbles entangled in the herbaceous matter 

 render it more buoyant than it would otherwise be, and en- 

 .able it to carry with it, and to sustain at the surface, any 

 accidental filth of the liquor: and the scum thus produced 

 is by its own nature sufficiently tenacious to be separable by 

 the skimmer, or by drawing away the depurated juice from 

 beneath it. 



But, if the buoving bubbles be expelled by greater heat 

 and the commotion of boiling, the scum will be broken into 

 the liquor. 



The skimmer will now avail nothing ; but the herbaceous 

 matter, once thrown out of solution, will subside with the 

 filth, in an hour, in a cooling quiescent liquor,, and will 

 leave it transparent, although it still retain that quantity of 

 herbaceous matter, which the water, with the last adherent 

 portions of carbonic acid, can dissolve. 



But as this depuration by subsidence cannot be awaited 

 without injury to the juice, the foul scum aught to be re- 

 moved before the liquor boils. 



In consequence of this limited solubility, the residuary 

 herbaceous matter becomes extricated afterwards in quan- 

 tity proportionate to that of the watery solvent which is ex- 

 pelled by evaporation, and the reduced liquor becomes tur- 

 bid by the extricated herbaceous particles. 



However often the process of evaporation is stopped, and 

 the liquor is depurated to perfect transparency, by subsi- 

 dence or otherwise, it will become turbid again, by the 

 deposition of herbaceous dregs, when the evaporation iS 

 renewed ; and it will thus yieW dregs to the end, or until 

 the residuary liquor becomes so far saturated with sugar as 

 to be incapable of holding the less soluble herbaceous matter 

 in solution. 



All this takes place whether a moderate dose of temper 

 be used or not. But the cleansing by subsidence is quickest 

 when temper is used. 



To ascertain the true use of temper, we must advert to its 

 agency on herbaceous matter, carbonic acid, and melasscs^ 

 icid. 



Lime powerfully attract? carbonic acid ; and although 

 • • .^ lime 



