LETT ER S
QUESTION: HOW can YOU
leach bigger tonnages at lower oDerating costs? tegrated and draw a line from it to the curve. Lock the compass legs apart a distance about equal to a “diagonal” of,{ the figure to be measured. Then hold the compass perpendicular to the plane of the curve with the tip on the starting point and the blade somewhere near the middle of the plane. Mark its starting point. Now holding the tip loosely, slowly trace the line out to the curve, go around the curve, along appropriate axes, and then return to the starting point. The “hatchet” will follow dutifully, but since it can only rotate or travel parallel to itself it will trace an odd path. Mark its stopping point. T h e area traversed is the product of the span of the compass and the distance between the initial and final positions of the hatchet. T o assure that the compass span hasn’t changed during the traverse, it is wise to compare the distance between the starting point of the tip and the initial and final blade positions. Obviously, one should try this gadget on some known areas to get the hang of it-circles and squares. If the distance traversed by the blade is too short for precise measurement, shorten up on the span of the compass. If the blade’s journey causes it to leave the paper, start the blade in a different spot and/or traverse in the opposite direction. Although it’s fairly obvious how the optical differentiators work, I have never understood the integrator. If any reader has a n explanation, do send it along. We would also like to have knowledge of your favorite gadgets, problems, or whatever else will interest Industrial Chymists.
With a French
stationary Basket ExtractorI
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Units Again Sir: This is in response to your invitation for comments on the article by Dr. Adrian Klinkenberg, “American Engineering System of Units and Its Dimensional Constants g,,” [IND. ENG. CHEM.,61 (4), 53-59 (April 1969)l. We are chagrined to have made the errors in units which he noted in ref. 41. T h e reason (but not excuse) for our carelessness was the knowledge that all of our work was actually done and expressed in dimensionless terms. T h e problem of units is vexing to both undergraduate and graduate students, and I have done considerable experimentation to discover what is most successful in teaching. I have concluded that it is best to stick to the M L T system in my presentations and thus avoid the distraction of the extra terms g c and J . However they must regularly utilize data in terms of Btu’s, calories, and pounds force. Hence I must also teach them to convert to the M L T system from the F M L T and F M L T Q systems. I a m appreciative to Dr. Klinkenberg for an enjoyable and constructive article. Stuart W. Churchill The Carl V. S. Patterson Professor of Chemical Engineerzng University of Pennsylvania Phila de& hia, Pa. 19 I04
THE FRENCH OIL MILL MACHINERY CO. Piqua, Ohio 4 5 3 5 6 . A/C 513-773-3420
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JANUARY 1970
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