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CANE SUGAR.Then since the vapour at the moment of its formation is at a greaterpressure than that already formed, and since the temperature of a boilingliquid is equal to that of the vapour which it gives off, it follows that themean temperature of the juice in ebullition is greater than that of the vapourin the vapour space.Again, the juice is emulsioned with the vapour it gives off and this hasa tendency to diminish the density of the boiling juice. Now to obtain anidea of the volume of the contained vapour, Dessin recalls the phenomenonobserved when an evaporator stops boiling, namely, that the level o£ tboliquid falls. This fall in level, which is 3 inches in extent, Dessin takes asgiving the volume of the contained vapour.Take the case of the third body of a triple, the vacuum being 25 inches,the vessel 6 feet internal diameter, the tubes 4 feet long, 2 inches diameter,and 630 in number. The total volume of the juice is the volume of thetubes + the volume above the tube plate —the volume occupied by the vapour.We have, then, at restDuring ebullition the total volume is that found above + that occupiedby vapour = Π X 3 x 3 x 1 / 4c. ft. = 7.0 c. ft. The total volume duringebullition is then 76.1 c. ft.The finally corrected densities of the juices then appearThe vapour then in the third vessel will have to raise a column of liquid ofmean height 27 inches, and of density 1.116 ; this is equivalent to 2.20 inchesof mercury or 1.09 lbs. per square inch. The vapour itself was taken at apressure of 2.42 lbs. per square inch, so that the pressure of the vapour at themoment of its formation is 2.42 + 1.09 = 351 lbs. per square inch, correspondingto a temperature of 147° F.; that of the vapour was 132°F., adifference of 15° F.Similarly for the second body a difference of 7° F., and for the first of4° F. are found.The efficient fall in temperature from body to body is thenor 76.5 per cent. of what would be the case if the height of juice in ebullitionwas zero.312