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CANE SUGAR.Witeowitz Heater.—In Fig. 172 is shown in section the radiatingheater of Witcowitz. It consists of a forged steel body, aa, through whichpass at right angles to each other a series of tubes, bb. The juice circulatesthrough these tubes, the heating steam being without the tubes and withinthe steel body ; the condensed water and heavier gases are drawn off at c, thelighter ammoniacal gas at d. A very rapid circulation is claimed for thisdesign ; it is usually applied to the horizontal form of evaporator describedabove, and is also used as a heater in saturation and defecating tanks, and iscapable of application to the vertical form of evaporator.Express System. 5 —Another modification of the heating surface,known as the 'Express' system, is shown in section in Fig. 17$. It consistsof a belt, aa, in which are arranged the tubes which form the heatingsurface; as in the Witcowitz heater above described, the juice circulatesthrough the tuhes b, steam enteringthe collector box at c, and the condensedwater passing away at d.The collector box is set at an anglefollowing the slope of the saucerof the effect, usually at an angleof about 30° from the horizontal;the tubes are about 18 inches long.In an effect entirely on this systemthere will be a second calandriaabove the one shown and placed inregard to it as a mirror image tothe object. This design can bereadily applied to effects with theordinary vertical tube calandria, abelt being added to the effect below Fig. 172the existing calandria in which the additional heating surface is placed.The 'Express' system has been further developed by placing within theshell of a vessel an inner shell of the same diameter as the calandria andleaving a space of some inches between the two walls; a colder and heavierliquor collects here, which tends to descend and thus to form an inducedcirculation.Incondensible Gases.—In the process of evaporation a certainquantity of incondensible gas is formed, and in addition some air enters withthe steam and through leaks in the apparatus. These gases have a corrodingeffect on the apparatus, and if allowed to accumulate seriously diminish theefficiency of the heating surface. In the first vessel they may ho removed bya cock opening into the atmosphere, but as steam also will pass out, thisprocess is uneconomical, and it is preferable to pass the gases successively302