18 



the lime which has not already been rendered insoluble by combina- 

 tion with organic acids and other impurities in the juice is precipi- 

 tated as carbonate of lime. The "carbonated" juice is very turbid, 

 and is pumped through filter presses (pis. 27-29 of the exhibit), which 

 remove the insoluble matter suspended in it. This insoluble matter 

 consists of carbonate of lime, lime compounds formed with the impu- 

 rities contained in the juice, proteid bodies rendered insoluble by the 

 heat, etc. The clear juice is again treated with lime and carbon 

 dioxide, and again filtered. The clear juice coming from the second 

 " carbonatation " is then bleached with sulphurous acid, applied in 

 the form of the fumes of burning sulphur. . The bleached juice, after 

 being again filtered, is ready for the evaporator. 



EVAPORATION OF THE JUICE TO SIRUP. 



The juice, after having been purified by the method described, is 

 evaporated to a sirup containing about 50 per cent of water and 50 

 per cent of solid matter. The solid matter is made up of 40 to 45 per 

 cent of sugar and 5 to 10 per cent of organic and inorganic substances 

 other than sugar, which, to a greater or less extent, prevent the crys- 

 tallization of the sugar. 



In the modern sugar factories the juice is evaporated in multiple- 

 effect vacuum evaporators heated by steam. These evaporators con- 

 sist of from two to four closed evaporating pans which are heated by 

 steam which circulates through copper pipes arranged in the lower 

 part of the first pan. They are called" multiple effect" because 

 more than one effect of a given portion of steam is obtained. For 

 example, exhausted steam from the pumps and engines or steam 

 drawn directly from the boilers is used to heat the first pan. The 

 steam generated by the boiling juice in this pan is collected, and used 

 to heat the second pan. The vapor of the second pan is in turn used 

 to heat the third pan. In the case of a quadruple-effect evaporator 

 the vapor in the third pan is used to heat a fourth pan. The vapor 

 from the last pan is conveyed to a condensing apparatus in which it 

 meets a spray of cold water, which condenses the vapor to form water. 



Air leaking into the apparatus and noncondensible vapor are 

 removed from the condenser by means of a vacuum pump, which is 

 kept constantly in action. The juice in the first pan boils at approx- 

 imately the atmospheric pressure. The pressure in the following 

 pans is successively reduced from pan to pan, the liquid in the last 

 pan boiling in as nearly a complete vacuum as is practicable. Evap- 

 orators of this type are called "double," "triple," or "quadruple 

 effects " accordingly as there are two, three, or four pans. The opera- 

 tion of the evaporators is continuous. The juice is pumped into the 

 first pan while the finished sirup is pumped out of the last pan in a 

 continuous stream. The collection of photographs already referred 

 to contains sectional and exterior views of two types of evaporators 

 (pis. 30 and 31). 



