THE CARBOHYDRATES PRODUCED IN CROPS 113 



cane with a little water, as much as 90 per cent, of the j uice 

 can be extracted. Excepting under the most primitive 

 conditions, lime is always used for removing many of the 

 impurities in the j uice. In the field methods of manufacture, 

 adopted in India, the lime is added until the natural colour 

 of the sugar cane juice, which acts as an indicator, shows 

 that neutrality has been reached. The liquid is then boiled 

 down, and very carefully skimmed. In more elaborate 

 and carefully industrialized systems a slight excess of lime 

 is used, then filtered, the excessive lime removed, by carbonic 

 acid, and again filtered. Some of the proteins are precipi- 

 tated on boiling in any case. In primitive systems the whole 

 material purified by skimming is boiled down until it becomes 

 very thick, when it is poured into moulds. The moulds 

 often consist of holes in the ground, lined with cloth, so 

 that some portion of the molasses drains away. In such 

 a case a brown sugar is obtained. Where it is desirable to 

 get a very white sugar the boiling-down process takes place 

 in a vacuum pan. Sugar is converted into caramel, a brown 

 colouring matter, by the action of heat, but by reducing 

 the pressure, and therefore the boiling point, the heat is 

 lowered to less than the temperature at which sugar begins 

 to caiamelize. Further improvement can be adopted by 

 separating the molasses from the sugar by a centrifugal 

 machine. A small centrifugal machine, worked by hand, 

 can be obtained for field use. In India, brown sugar is 

 preferred to white sugar, and hence little effort is made to 

 carry the purification to any extent. The supply of fuel 

 is always an important point in the manufacture. The waste 

 cane, if dried, makes a useful fuel, and the dried side leaves, 

 unless required for fodder, can also be used as fuel. In 

 India the upper leaves are used to feed the bullocks. For 

 the satisfactory cultivation of sugar cane nitrogenous 

 fertilizers are essential, and in experimental work conducted 

 in India quantities of from two to five hundred pounds per 

 acre of nitrogen have been used, although the larger quantity 

 seems unnecessary. Other manures, such as phosphatic and 

 potassic ones, are sometimes necessary, but not to anything 

 D. 8 



