idew from everywhere Environmentally Safe Spray .Cans Industrial Chemical News (2, 7[1981]) reports on the reaction of sodium bicarbonate with citric acid to produce carbon dioxide as the basis of an alternative propellant in spray cans. The uniqueness of the application is that the reaction takes place in a pouch stored in the can. As carbon dioxide is produced, the resulting pressure causes the pouch to expand and dispense the product. The bicarbonate and acid are both stored i n the pouch, the citric acid heing released as the product is used. (Unfortunately, the means to release the citric acid was not discussed.) Among the advantages of the new propellant are Hrplaues thaw fl~orocarb~ns which m m f e the lung, and can produce arrhythm~nof the heart (2) I'revtnts the uxrdatlon ul the stured prcdurt because alr can he excluded (3) Eliminates the chilling effect of the spray which occurs when the propellant expands (4) Operates at a wider extreme of high and low temperatures ( 5 ) Dispenses a range of materials from fine powder to highly viacous Vaseline (1)
Lecture Experiments With Paper by Doc the Clown How Does Your Paper Tear? Effect: Each student is given a sheet of newspaper and asked to tear the sheet lengthwise and then tear one of the pieces widthwise. Student observations are then requested. Consensus of observations usually include: (1) Lengthwise tear is straighter than the widthwise tear (2) Fibers are present along the edges
edlted by DOUGLASD SMITH Gutltord High School eockford
,no,s 6 1 1 t l
Feel the Color. Effect: You can tell which of four cards: red, yellow, green, or blue has been reversed while vour back has been turned. The usual explanation is that you can wll whtch has been reversed hy feeling the d o r . 6 0 , you lie a littlr ) Cause: Rectangles are cut fro& poster board so you bend the cards along the diagonals. One axis is more resistant to bending than the other. So, if you initially line up the cards with the most firm axis from upper right to lower left, the reversed card will have its most firm axis from upper left to lower right. Again, the resistance is based on the alignment of the fibers in the oosterhoard. This magician's packet effect goes t,y the name .'Feel the Colur Trick" and costs about $1.50.
An Idea from Ireland In past columns we have tried to convey the value of con ventions in obtainine stimulation. renewed enthusiasm.. and alwrnative ways uf &hing or demonstrating chemistry. At the Grh International Conferenre on Chrmical k:ducation. I had the pleasure of talking to Randy L. Henley, the editor bf Science, the official iournal of the Irish Science Teachers Association. Here is an idea from the magazine for constructing simple electrolytic cells:' ~~~~~~
Holes to take No. 9 rubber stoppers are cut in the bottom of a polypropylene beaker (100 or 250-ml) with a cork horer heated in a Bunsen flame. Carbon electrodes are nushed into holes in two stoppers and fitted as shown. (Carbon rods 200 mm long can be broken into three.) The apparatuscan he supported by a pipeclay triangle on a tripod.
(3) Layering is seen along the torn edges Ditto paper is then torn by each student to see if similar observations are made. (Hopefully you will find the class rehel creasing his paper before tearing and finding that he can force the tear to be straight along the width or diagonal.) The brand of paper my school provides results in about ten percent who find that the "widthwise tear is straigbter."The basis has been laid for a good class discussion. At this point, I prefer to have the students go home and make observations on magazine pages, carbon paper, etc. (I urge this since i t then gives the parents a chance to become involved without havine to show how little high school chemistry they have retainel) Causes: Newsprint is manufactured by using wood fibers that have a length seven to ten times the width and that are arranged almost parallel to each other. When the newspaper is torn along the length, a straight edge results. ~ e w s ~ a iise i purposely made with the fibers parallel to give the paper strength as i t runs through the presses. Other paper is made to have the fibers in a random pattern, such as handmade paper or paper for labels. Labels, especially beer and cigarette, may have many colors applied, and it is important that the paper not shrink while it is heing printed. ~
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This bi-monthly feature presents a potpourri of thoughts and items that high school chemistry teachers have found useful in their classr m . SuMnaries and absbans of Mides that have eooeared ~- in recent ISSUBS of science journals fromaround the world are also highlighted in this feature.Your contribution and ideas are welcome and encouraged. ~
400
Journal of Chemical Education
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Construction diagram for simple elecbolytic cells.
Errata In the May 1981"Ideas from Everywhere" column, credit was not given to material originated by Edward L. Waterman J. CHEM.EDUC.57,148 [1980]). The author of the article, Dr. Ronald DeLorenzo, regrets this oversight.
' Science, 17 [ I ] , 47 (1981).
