Correspondence
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CENTIGRADE-FAHRENHEIT TEMPERATURE CONVERSION DEAREDITOR: EDUCATION, page In the December issue of the JOURNAL OF CHEMICAL 2946, I noticed a topic headed as above by JOSEPHG. BLANN,David Starr Jordan High School, h s Angels, California. What appears to the present writer to be a more simple means of conversion is the following: (1) To Centigrade add 40" multiply by 9/5 and subtract 40' or To Fahrenheit add 40' multiply by 5/9 and subtract 40". In either case add 40" at the beginning and subtract 40' at the end. If one is going from low to high (C. to F.), multiply by the improper fraction, 9/5. Or if one is going from high to low (F. to C.), multiply by the proper fraction, 5/9. There is really no formula to get wrong and this is the easiest method I have ever seen for converting one temperature into another. (2) Another easy conversion is to take as a basis 20°C. equals 6S°F. With that one can change C. to F. by solving how 20°C. equals 68°F. 20DC.multiplied by the improper fraction, 9/5, and 32' added to the result is the only way 20°C. can equal 6S°F. This being true then, one always has a ready means for conversion. By working this backward one can go from F. to C., thus 68'F.
- 32'
=
36' X 519 = 20%
Other numbers, for example, 100°C. and 21Z°F., could be used instead of 20°C. and 6S°F. ALFREDM. EWING* Tae Omo SmrB U m e n s m COLUXBUS, OWO
'
* Graduate student, physical chemistry. DEAREDITOR: EDUCATION carried an TEe December issue of the JOURNAL OF CHEMICAL article on pages 2946-7 by JOSEPHG. BLANN,on the topic of conversion of Centigrade to Fahrenheit by referring to the boiling point of water, instead of the freezing point of water as the standard texts employ. This article created a great deal of interest for me, because I felt it was just as difficult to remember to use 212" and 100' as boiling points and substract the correct numbers at the right time, as in this illustration: 20°C. = ?OF. 20°C. is (100 - 20) 80°C. below the boiling point. Therefore, take 9/5 X 80 = 144'F. below the boiling point or 212' - 144' = 68°F. 370
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I believe most problems will be dropped with the answer 144°F. instead of 68°F. For the past ten years I have been using and teaching a conversion scheme that seems to satisfy the need as well as to satisfy the student. The standard point of conversion in this scheme is -40°C. equals -40°F.
Therefore, if I were to change 20°C. to F., the plan is to add 40, multiply by 9/5, subtract 40 and the result is 6S°F. Also to change 6S°F. to ?T., the plan is to add 40, multiply by 5/9, subtract 40, and the result is 20°C. To state these plans in algebraic formulas
for the algebra student is advisable. This little puzzle of changing temperature scales in science classes causes very little fear and worry for students and teachers in our high-school science department. Since the standard texts use the old 32' plan of conversion, the origin of the -40' plan cannot be indicated, in spite of the fact that it has been used for ten years producing successful and pleasant results. HERMAN W. WOODS
A SHOW WINDOW FOR THE CHEMISTRY DEPARTMENT We hear it said that every teacher must be a salesman, selling his subject. What more legitimate, then, than a salesman's show-window? I wished for one for several years. Interesting things are brought, or develop on o w hands, and only a favored few see them ordinarily. Last year I removed a "dead" exhibit of zinc plant "intermediates" from a case in the hallway outside my door, put in a lamp-bulb, and every few days introduced a "live" exhibit. There were a "chemical garden," surface tension boats, Geissler and X-ray bulbs which worked with a push-button, a rock that floated on water (volcanic tufa), a density exhibit with mercury,
