MANUAL FOR SUGAR GROWERS. 



109 



steam from some suitable source ; the vapour or 

 steam generated from the boiling juice passes by 



Fig. 17.— Diagram of tnple-eft'ect apparatus. 



means of the conclucting-pipe into the steam-drum 

 of Vessel 2, and the steam from Vessel 2 passes into 

 the steam-drum of Vessel 3. Now, in Vessel 1 the 

 vacuum is but very slight, so that the boiling-point 

 of the liquid, and consequently the steam produced, 

 have a temperature of about 180° F., corresponding 

 to a vacuum of about five inches ; in "Vessel 2 a 

 vacuum of about fifteen inches is maintained, and 

 in consequence the boiling-point in this vessel is 

 about 150° F., so that there is a difference of 30° 

 between the temperature of the steam and the boil- 

 ing-point of the liquid, a sufficient difference to 

 cause the liquid in Vessel 2 to boil, and thus supply 

 steam at 150° F. to the steam-drum of Vessel 3, in 

 which the vacuum is maintained at about twenty- 

 seven inches and the liquid boils at 120° F. Thus 

 the liquid in Vessel 3 is boiled by the steam from 

 Vessel 2, which has a temperature 30° above the 

 boiling-point of the liquid in Vessel 3. Suitable 



