VACur:M PANS. 353 



the cylinder -when first entering the machine, which is operated by 

 cams. The machine is rotated by means of outside gear on the con- 

 vey cylinder. 



The current of air constantly passing through the machine carries 

 off the moisture from the sugar through a pipe, and the dry sugar is 

 delivered cool from the end into which the cold air is passing, so that 

 it does not cake, and can be immediately barreled, and will not cause 

 the barrels to shrink. 



The following calculations of the practical workings of the vacuum 

 pan, are from the Encyclopedia of Chemistry, Vol. II, p. 903, Lip- 

 pincott. 



" If 30,000 pounds of sugar containing 10 per cent of water, are 

 produced in 2 hours from pan-liquor containing 50 per cent of water, 

 equal to 27^° Beaume of density, then 27,000 pounds less 3,000 pounds 

 of water would be evaporated, which, at 28° vacuum, would equal 

 5, 333, 33-4 cubic feet of vapor, and the velocity of this vapor through 

 a pipe of two feet in the cross section, would be 741 feet per second. 



If the condensing water was at the temperature of 60°F., and should 

 escape by the vacuum pump at a temperature of 90°F., 24,000 pounds 

 of steam would require 84,480 gallons of water for condensation, or 1 

 gallons of water evaporated would require 28 gallons of water to 

 condense it. 



The steam needed to evaporate 24,000 pounds of water in the vacu- 

 um pan, would be, at 30 pounds pressure above the atmosphere, 28,208 

 pounds, without any allowance for waste. 



An open pan would require only 14 j^er cent more heat to evaporate 

 the same amount of water." 



It wiU thus be seen that the advantage of the vacuum pan (and 

 it is unquestionably great) is not found, as is by many urged, in its 

 saving of fuel or steam, for that is small, and, besides, the apparatus 

 is expensive, and requires expert supervision. 



The vacuum pan enables the juice to be concentrated at a low tem- 

 perature, thus preventing burning entirely, and the inversion of the 

 sugar to a great degree. 



The heat of the vacuum pan is generally the direct steam from the 

 boiler, but, on account of the low temperature necessary to secure ac- 

 tive boiling, it has been found economical to use the waste steam of 

 the sugar mill in the coils. As an improvement upon the vacuum pan , 

 there have been devised what are known as the double or triple effects, 

 to be shortly described. 



In order, also, to avoid the effect of high temperatures upon the 

 sugar, an apparatus similar in construction to the Cook Pan, see jiage 

 23 



