450 CHAPTER XXII 



5. After a time the mother Uquors become too charged with impurities 

 to be returned. They are then treated separately, two operations being 

 sufficient to exhaust them. In all, the mother liquors are returned from 

 25 to 30 times. 



The second process of Steffen^^ is known as separation, and this of all the 

 saccharate processes is the one that has survived. Its operation falls into 

 three parts : — 



1. Preparation of a very finely divided quicklime. 



2. Formation of a tribasic saccharate in the cold. 



3. Extraction and purification of the saccharate. 



In preparing the lime, a very pure non-siliceous stone is used, which is 

 burned out of contact with the fuel. The burnt lime is brought by some 

 means to a very fine state of division. In the United States, Raymond 

 mills are exclusively employed. These mills separate the fine lime from the 

 residue by means of an air blast. 



In the second operation the molasses at a density of io°-i2° Brix is 

 cooled down to a temperature of 5°-6° C, and the powdered quicklime is 

 gradually added to the material until 210 parts of lime per 100 of sugar 

 have been used. During the operation, the molasses is constantly agitated, 

 and its temperature is not allowed to rise above 13° C. At the completion 

 of the process there is obtained a pasty mass consisting of tribasic saccharate 

 and lime. This precipitate is filtered off and washed with cold water, 

 after which the washed cake is used in the treatment of fresh juice, The 

 filtrates contain some sugar, and this is recoverable by boiling when an in- 

 soluble saccharate forms, which is recovered by filtration. In some cases 

 the washings are run to waste as not being worth while treating. 



The lead saccharate process has been lately developed by WohP* and by 

 Kassner.i^ Molasses mixed with 80 per cent, of water is kneaded with 

 litharge in the proportion of 150 parts lead oxide to 100 of sugar. The 

 pasty saccharate is separated and decomposed as in the other schemes, 

 affording a liquor of 98-99 purity. Difficulty of regenerating the lead and 

 objections to the use of lead in the preparation of an article of food have 

 prevented any extension of this scheme. 



Osmosis}^ — It follows from the above sections that if the salts could be 

 removed from an exhausted molasses, the conditions of solubility of the sugar 

 would be altered and a further portion would be capable of crystallization. 

 About 1850 a method of effecting this was worked out by Dubrunfaut. The 

 principle of his process known as osmosis is as follows : If a concentrated 

 solution of any soluble body be separated from a weaker solution or from 

 water by a semi-porous membrane, such as parchment, the two solutions 

 will pass through the membrane until they are of the same concentration. 

 The rate at which this osmosis or diffusion takes place is not the same for 

 all bodies ; inorganic salts such as potassium chloride diffuse much faster 

 than sugar ; hence if a solution of molasses be separated by a parchment 

 membrane from water, a greater proportion of salts wiU pass through the 

 membrane in a given time than sugar. An osmogene is an apparatus to 

 effect this separation ; it consists of a structure similar to a filter-press, 

 in which are held a series of wooden frames, shown in elevation in Fig. 273. 

 Between each frame are placed sheets of parchmentized paper, pierced at 

 the angles to correspond with the apertures shown at A, B, C, D, and at 

 A ', B ', C ', D ', in Fig. 273, At b and c in the one frame, and at a and d 



