402
ISDUSTRI.4L AKD ENGINEERING CHEMISTRI-
ratio of specific gravities between the water layer and the tetrachloroethylene layer; and any change in the ratio will vitiate the reading. Furthermore, the scale is shortened in length which in turn renders the reading somewhat less accurate.
Summary A trap is described which is suitable for use in determining moisture by distillation with immiscible liquids heavier than
VOL. 10, NO. 7
water. Its operation is independent of thermal environment, and requires no adjustment of reflux rate. The use of a surface tension depressant facilitates the correct reading of the water volume.
Literature Cited (1) Bailey, A. J., ISD. ENG.CHEY.,Anal. Ed., 9,568 (1937). ( 2 ) Wilkes and Wickert, INDENG CHEM.,29, 1234 (1937). RECEIIE D Xlarcli 2 2 , l Y 38.
An Easily Constructed Orifice CHESTER P. BAKER
ARD
WILLIAM -4. RIcGRATH
Northeastern University, Boston, Mass.
T
HE velocity of a fluid in a pipe line may be determined by inserting an obstruction and measuring the change in static pressure resulting from the change in the velocity produced by it. The relationship between the size of the obstruction and the pressure drop is convertible into the line velocity. The standard orifice makes use of this principle.
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B type of orifice construction which has been found very satisfactory is shorn in the drawing. A close examination will reveal that the flanged castings of the standard orifice have been replaced by an ordinary union threaded throughout its length with a shoulder formed by the pipe in the female side to hold the orifice plate. The threaded straight sections of pipe extend to the orifice plate. The pipe ends may be machined or a lead gasket used to make a water-tight bearing between the pipe and the orifice diaphragm. Proper machining will allow the orifice plate to be held rigidly and a t the same time not lose the advantage of the ground joint of the union. When a lead gasket is used, a tight joint can be made which is satisfactory a t low pressures. RIanometer openings
can be drilled and tapped without difficulty after the other parts have been assembled. The orifice described can be constructed from ordinary pipe fittings with the minimum of shop equipment. The interior of the orifice chamber is smooth without expansion and contraction areas near the manometer openings. The
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orifice plate can easily be removed and the fluid allowed to flow through the line without the resistance of the orifice. The centering of the orifice ceases to be a problem in this type of construction, once the orifice opening has been made in the exact center of the disk which serves as the orifice plate. Care should be taken as with other types of orifices t o insert it in a straight pipe of sufficient length to equalize the turbulence caused by fittings such as elbows, tees, etc. The authors have found this type of orifice to be easier to construct, less expensive, and more accurate than others which use castings t o form the orifice chamber. RECEIVED April 9, 1938.
