February, 1923
I N D USTRIAL A N D ENGINEERING CHEMISTRY
AT Low RATEOF FLOW While 0.1 ft./sec. is extremely slow for pipe flow, it is very rapid compared to the customary velocity a t which water passed over a number of closely spaced steel sheets, as in the deactivator now used for removal of free oxygen from water. Also, if velocity increases the rate of corrosion so rapidly, the efficiency of a deactivator should be considerably increased if the velocity can be increased. The following apparatus was therefore constructed: A small experimental deactivator (Fig. 5) 8 in. in diameter and 4 ft. in height was used. I n order to obtain a higher velocity with the same time of contact, a system of alternate baffles was employed, composed of 26-gage black iron, between each of which was one of the regular soft steel sheets used for deactivation purposes. These baffles fitted very closely to the inside of the deactivator so that the water was compelled to pass over them. By this means the velocity could be increased about 13 times, covering the range 0.0043 to 0.10 ft./sec. All the sheets were freshly pickled in sulfuric acid and thoroughly washed before use. After a series of runs was made the sheets were
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removed, recleaned, and the deactivator flied in the usual way without the baffles. Duplicate runs were then made. Five valves giving outlets from various sections of the deactivator enabled various times of contact to be included in the same run. Thus was the time of contact as well as the temperature kept constant for various values, the only variable being the velocity. Fig. 7 gives the experimental results, which show that the effect of velocity even a t this low rate of flow is quite pronounced, increasing the oxygen removal from 10 to 25 per cent. I n Fig. 6 is plotted the specific rate of corrosion in the deactivator, together with the specific rate of corrosion a t 150" F. of the three sizes of pipe. From this it is shown that the specific rate of corrosion in deactivators falls in the lower velocity range of pipe corrosion when we consider the specific rate of corrosion from a velocity standpoint alone. The rate of corrosion in deactivators is naturally higher than we would expect from the velocity of the water as the direction of flow was changed frequently by a closed system of baffling.
A n Internally Heated Laboratory Vacuum Pan' By J. F. Brewster LOUISIANA S U G A R EXPERIMENT STATION,
HE ORDINARY laboratory arrangement for vacuum distillations consisting of two round flasks, one heated externally serving as still or pan, the other cooled by running water serving as a condenser, is unwieldy and slow in action. I n order to test the efficacy of internal heating the apparatus described herein was devised. The body of the pan consists of an inverted bell jar 6 in. in diameter, with ground flange and wide mouth; this is supported by an asbestos ring resting on a tripod. The mouth of the body is closed by a iubber stopper through which pass the feed and draw-off tubes of glass and the leads of the flat-wound heating coil of 5/~~-in. copper tubing. When the spiral coil is wound the ends of the tubing are brought close to the center and bent at right angles to the spiral plane, being left long enough to pass through the rubber stopper and to provide for connection, one to the drain, the other to the source of heat. The top of the pan is the glass dome of the ordinary vacuum distilling apparatus shown in the catalogs of dealers in laboratory apparatus. This is fitted to the body by means of a rubber gasket. A second bell jar or the tubulated top of a vacuum desiccator may very well serve as the dome of the pan. The rubber stopper closing the mouth of the dome carries the thermometer and the glass exhaust tube leading to the condenser. The pan coil may be connected by means of brass unions or rubber tubing to the coil of a Fletcher instantaneous water heater. With a good working
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1
Presented before the Division of Sugar Chemistry at the 64th Meeting
of the American Chemiral Society, Pittsburgh, Pa., September 4 to 8, 1922.
N E W ORLEANS,L A .
pump a vacuum of 27 to 28 in. of mercury may be maintained; consequently it is unnecessary for the pan coil to be brought to a very high temperature and the Fletcher heater may be replaced by a helix of copper tubing heated by a Bunsen flame. The temperature of the water entering the coil may be controlled by varying water or gas pressure. Several types of condenser are suitable for vacuum distillation. The Soxhlet ball condenser is small and efficient, or a closely wound helix of block tin or copper tubing in. in diameter with water jacket may be used. The latter is supported in a vertical position and discharges into a filtering flask. If a mechanical pump is at hand the distillation may be made continuous by withdrawing the condensate when necessary. -Rubber Gaskef It so happened that all the parts of the apparatus described above, excepting the copper coil, were on hand in our laboratory, so that a very small financial outIay is represented. The parts may readily be duplicated since they are stock materials carried by laboratory supply houses. With interior heating, distillations under reduced pressure may be accomplished with a great saving of time over that required with externally heated apparatus, owing to the large heating surface and the heat conductance of the coil. The boiling of cane sirup to massecuite with this apparatus requires one-third or less time than with the flask and water-bath arrangement. It has also proved very satisfactory for reducing the volume of alcoholic plant extracts.
