340 SOEGECUM. 



It would appear, however, that this principle possesses some valu- 

 able features, especially if so contrived as to complete the evaporation 

 of a given quantity of juice at once ; for it is found that the evapora- 

 tion from a thin film is rapid, even at temperatures far below the boil- 

 ing point, as is known to everybody in the familiar process of drying 

 clothes by hanging them upon a liue. The principal objection urged 

 against all evaporators of this class, does not appear, as yet, to have 

 been overcome in practice, viz.: the drying and adhering to the heated 

 surfaces of a gradually increasing crust of sugar, which not only pre- 

 vents, to a great extent, evaporation, by being a poor conductor of 

 heat, but results in the inversion of a large portion of the sugar which 

 is thus adhering. 



Pan Scale. 

 In the process of evaporation, especially with the open pan, con- 

 siderable trouble arises from the formation of a white scale upon the 

 pan, which not only retards evaporation, but becomes, when loosened, 

 incorporated with the syrup. An analysis of this scale, shows it to be 

 composed, when deposited from sorghum juice, of a lime salt of aconitic 

 acid. This acid has been detected in the molasses of sugar-cane, and 

 it is probable that a similar deposit found upon the evaporators of 

 sugar-cane juice, and generally called lime, is of like composition. 

 The average of three analyses of scale, from a concretor used for the 

 juice of sugar-cane, gave the following composition: 



ANALYSIS OF PAX SCALE. 



Per cent. 



Moisture 5 S6 



Orsiaiiie 18 05 



Insoluble 14 24 



Sulphuric acid 96 



Phosphoric acid 8 43 



Lime 37 98 



Iron 2.61 



Alkalis, etc 12 37 



100.00 



The character of the organic matter in the above is not given, but 

 it is by no means improbable that this scale is in part composed of the 

 same salt. The practical question concerning it, is its removal from 

 the pans, since, by its poor conducting pawer, it will cause the pans 

 to be heated even red hot, thus burning them out ; and besides, if, 

 cracking loose, it admits the syrup to this red hot pan, burning is in- 

 evitable. 



The use of diluted acids, sulphuric, hydrochloric, or sven vinegar, 

 has been recommended for its removal ; but, if used, the pan must uot 

 long be in contact with these stronger acids, and, after their use, the 



