OTHEE AGENTS IX DEFECATION. 303 



placed upoD a blanket filter, until it has so far dried as to begin to crack. 

 Avheii it may be kept for use in defecation, 



TLie method of using this is, to mix it up iuto a cream and applv in 

 the amount above stated, using for each 100 gallons as much of the 

 finings as would be made from 2^ pounds of alum. 



The details of the process as given, in " Sugar Growing and Refin- 

 ing, " are as follows : 



The ju'ce is strained before entering the defecator, and is then gently heated ; 

 to each 100 gallons of juice, 2 ounces (more is necessary with sorghum juice) 

 of finely sifted quick-lime are made into a cream with water and added to the 

 contents of the defecator, with thorough stirring, and the heat is increased to 

 82° C. (180'^ F, ), until a thick crust forms on the surface and shows a disposi- 

 tion to crack. This may take 15 to 20 minutes after the addition of the lime; 

 if it is very slow in forming, the heat may be raised to 93° C. (200° F.), but not 

 beyond. When the crust of scum has formed and shows signs of cracking, the 

 heat is withdrawn, and the juice is allowed to stand for 10 minutes, when it is 

 drawn off through a fine strainer into a second vessel, called the precipitator. 

 Here, again, the juice is heated up to the boiling point, but is not allowed to 

 boil, and the scum is removed as fast as it forms. The juice is then boilf^d for 

 10 or 1.5 minutes, with constant skimming, and then the "finings" are added, 

 with stirring, and the boiling is continued for 2 or 3 minutes more, when the 

 juice is quickly run off into a subsiding tank, and allowed to rest for from 2 to 6 

 hours. It is generally then passed through charcoal filters, and thence goes 

 to the evaporators. 



It Avill be seen that the "finings " are composed of a ruixture of sul- 

 phate of lime, alumina, and lime, and that, in short, this mixture is 

 used after the removal of the scum of the ordinary lime defecation, to 

 effect the more comjjlete subsidence of the precipitate, which it does 

 mechanically. 



Porou.i alum, an impure sulphate of alumina, prepared by dissolving 4 

 ouDces of the salt in a gallon of water, and, after allowing it to settle, 

 pouring off the clear solution for use, is used in a similar way, for the 

 clarification of defecated juices and semi-syrups. 



Basic alum and defecating compound are two forms of alumina recom- 

 mended by certain manufacturers. They are prepared, being practi- 

 cally identical, by adding to a solution of porous alum (crude alumina 

 sulphate) a solution of sal-soda in water, until a slight permanent pre- 

 cipitate is produced. 



The materials are used in connection with the cream of lime in or- 

 dinary defecation, and also with the clay cream already referred to. 



A solution of water glass, basic silicate of soda, has been recom- 

 mended — the gelatinous silica which is produced mechanically carrying 

 down the impurities. 



The principal objection to several of these preparations is the intro- 



