SUGAR. 81 



scum on the surface of the liquor, to have Been produced, the fire 

 is then extinguished by the application of the damper. In this state 

 of the liquor, the greater part of the impurities, being different in 

 specific gravity from the pure saccharine solution, and being also of 

 such a nature as to yield more readily to the chemical action of heat, 

 are brought up to the surface in a scum. After this scum has been 

 sufficiently formed on the cooling liquor, this liquor is carefully 

 drawn off, either by a syphon, which raises a pure stream through 

 the scum, or by a cock drawing the liquor at the bottom from under 

 the scum. The scum in either case sinks down unbroken, as the 

 liquor flows ; and is now, by cooling, of such tenacity, as not to 

 bend to any intermixture with the liquor. The liquor drawn, after 

 this purification, from the boiler, is received into a gutter or chan- 

 nel, by which it is conveyed to the grand copper, or evaporating 

 boiler. If made from good canes, and properly clarified, it will 

 now appear almost transparent. In this copper the liquor is heated 

 to actual ebullition. The scum raised to the surface by the boiling 

 is skimmed off as it rises. The ebullition is continued till there be 

 a considerable diminution in the quantity of the liquor. The liquor 

 now appears nearly of the colour of Madeira wine. It is at last 

 transferred into a second and smaller copper. An addition of lime- 

 water is here made, both to dilute the thickening liquor, to detach 

 superabundant acid, and to favour the formation of the sugar. If 

 the liquor be now in its proper state, the scum rises in large bub- 

 bles, with very little discolouration. The skimming and the evapo- 

 ration together produce a considerable diminution in the quantity of 

 the liquor. It is then transferred into another smaller boiler. In 

 this last boiler the evaporation is renewed, and continued till the 

 liquor is brought to that degree of thickness at which it appears fit 

 to be finally cooled. In the cooler, a shallow wooden vessel of con- 

 siderable length and wideness, commonly of such a size as to contain 

 a hogshead of sugar ; the sugar, as it cools, granulates, or runs 

 into an imperfect crystallization, by which it is separated from the 

 melasses, a mixed sacchariue matter, too impure to be capable even 

 of this imperfect crystallization. To determine whether the liquor 

 be fit to be taken from the last boiler, to be finally cooled, it is ne- 

 cessary to take out a portion from the boiler, and try separately, 

 whether it does not separate into granulated sugar and melasses. 

 From the cooler the sugar is removed to the curing house. This is 

 vol. v. G 



