vacuum, boiling point could be readied at a lower 

 temperature ; that the sugar could not then be 

 damaged and the expense for fuel would be dimi- 

 nished. 



To attain this object, vessels have been constructed 

 that have no communication with the outside air, 

 then a vacuum has been created in these vessels by 

 pumping out th^ air they contained : then to preserve 

 the vacuum which would destroy the steam, the 

 steam is condensed by cold water. 



Such is the principle, of evaporation at alow 

 temperature in vacua. 



In using a series of vessels,in which the vacuum 

 is successively increased, the steam produced by the 

 working of the first vessel, may be sent to boil the 

 second, which thus become the condenser of the 

 first ; the steam produced by the second boils the 

 third, which becomes the condenser of the preceding. 

 Finally the steam produced by the boiling of the 

 third passes into the condenser which liquifies there 

 with cold water. This latter vessel is the only one 

 that communicates 1 with the air pump, which esta- 

 blishes the equilibrium of the vacuum in all the 

 vessels. 



The apparatus a triplc-e/frt is thus composed of 

 three boilers, or vessels closed from the exterior air. 

 They are cylinders of cast or sheet iron of 4 feet in 

 diameter by 8 feet in height. Each boiler has at its 

 base a space shut off from the rest, which is called 

 the steam chamber. The steam chailfber occupies the 

 whole space from one foot from the bottom to four 



