110 MANUAL FOR SUGAR GROWERS. 



air-pumps are attaclied to the apparatus, and pumps 

 to remove the condensed water from the steam- 

 drums, which, being under a pressure below that of 

 the atmosphere, require to be pumped out, except in 

 the case of the steam-drum in Vessel 1. 



The syrup flows in a slow, continuous stream 

 through the whole apparatus, and on the correct 

 adjustment of the rate of flow depends the success- 

 ful working of a multiple - effect apparatus. The 

 syrup is concentrated in the triple effect to a suffi- 

 cient density to be taken into the yacuum-i^an, in 

 which it is boiled to grain as above described. 



The principle is the same whether the series con- 

 sists of two, three, four, or more vessels. Various 

 improvements in the details of the parts of the 

 apparatus have been devised from time to time, in 

 order to increase the efficiency or to render the 

 working simpler. 



In some of the most improved evaporators of this 

 type the economy of working is very gi'eat, nearly 

 forty pounds of water being evaporated for each 

 pound of coal burned. It will be remembered that 

 one pound of coal will convert only f oui-teen pounds 

 of boiling-hot water into steam when the evaporation 

 is accomplished in ordinary open vessels ; indeed, 

 this is the theoretical quantity, and in practice the 

 quantity evaporated is very much less than this, 

 usually not more than eight or nine pounds. 



The latest evaporators aim at allowing the fluid to 

 be evaporated to enter Vessel 1, and, after flowing 

 over the steam-heated surface, to pass into Vessel 2, 

 and over the heating surface of this into Vessel 3 ; 



