360 SORGHUM. 



chinery. The quality of the sugar from the juice evaporated in 

 vacuum, and the greater quantity of sugar, or, more properly speak- 

 ing, the smaller quantity of molasses that can be obtained by this over 

 the fire system, is another and very important reason for its adoption. 

 If necessary, the vacuum pan, triple effect, and the different circuits 

 of juice and water about the house, can all be operated by one engine, 

 under the immediate control of the sugar master. 



Concretors. 



In each of the evaporators thus far described, the object has been 

 the concentration of the juice after defecation to a syrup, from which 

 the sugar, after crystallizing, may be obtained, by either draining off 

 the molasses, as with the muscovado, or open pan, finegrained sugars, 

 or by removing the molasses by means of the centrifugal machine, as 

 is done with vacuum pan large grained sugars. 



But, owing to increased expense and trouble attending the produc- 

 tion of sugar upon the plantation, and the greater economy which at- 

 tends the extraction of sugar where larger and improved apparatus 

 and greater skill in supervision is secured, many attempt only the 

 production ujDon the plantation of what is known as " concrete," i. e., 

 the defecated juices evaporated until, upon cooling, it solidifies to a 

 mass, which may be shipped readily, and from which the refiners may 

 readily extract the sugar. This concrete contains, of course, all the 

 impurities which remain in the defecated juice and are not removed 

 by skimming in the production of the concrete. 



In principle the concretor may be likened to a Cook Pan, by means 

 of which the defecated juice is allowed to flow over a long trough, ex- 

 posed, during its flow, to a heat which at first is sufficient to boil the 

 juice and raise the scum, and is afterward diminished so that the 

 juice, when at a density of about 25 to 30° Beaume, is not heated even 

 to 100° C. Generally, the time required for the concentration of 

 defecated juice to 30° Beaume is from 8 to 10 minutes. The syrup 

 thus obtained is, by means of revolving discs, similar to those de- 

 scribed under Surface Evaporation (page 339), still further evaporated. 

 This last evaporation is rendered more rapid by means of hot air, 

 which is forced by a fan over the film of syrup upon the discs, the last 

 evaporation being accomplished at a temperature below that of boiling 

 water. Scrapers continually remove the solidified juice from the discs. 

 The "concretor" is also used for the purpose of reducing the juice, 

 after defecation, to pan-liquor, for which it is well adapted : in this way 

 taking the place of tlie ordinary evaporators used for this purpose. It 

 would seem that the use of the concretor and the preparation of con- 



