Quick Method for Making Colored-Flame Flash Paper Sally ~ o l o m o n , 'Chinhyu Hur, Alan Lee, and Kurt Smith Drexei University, Philadelphia, PA 19104 Flash paper is nitrated paper that b u m s dramatically with an instant bright flash, a "whoosh" or "hiss" sound, and little or no residue. Flash paper that produces "flames from your fingertips" i s available in magic and novelty shops in tablets of 20 5.5 cm x 7.5 cmsheets or in packets lit and tossed containing four 20 cm x 22 cm sheets.%en in the air this paper burns with a brief intense yellowish flame visible to-aiarge audience. Procedures have been described previously for t h e preparation of both nitrated paper (1) and nitrated cotton (2,3). Avery fast method for making flash paper similar in size and burning properties to the commercial type i s described here. Detailed instmctions are given for the preparation, storage, and lighting of flash paper that burns with single colors (red, orange, yellow, green, blue, violet) or with combinations of these colors. This method reciuires no more than a n hour from the mixing of the nitrat& acids to the lighting of the paper . . and eliminates prolonged - dming p r o c ~ d n r e(1,2). ~ Demonstrations using flash paper can be introduced when discussing atomic spectroscopy, flame tests and qualitative analysis of cations, thermochemistry, t h e chemistry of nitrogen compounds or of carbohydrates and nitrocellulose. Procedure for Nitrating Paper Very thin paper such a s the cheapest single-ply toilet tissue works best. The nitrating mixture. which must be freshly prepared, is made by mixing 125 mL of concentrated HN03 with 100 mL of concentrated HzS04 in a very clean and d& l-L beaker. Caution: The concentrated acids should be handled in a hood with great care. This is enough to make about 100 pieces of flash paper measuring 5 cm x 10 em, a little longer than the commercial papers. The nitric acid must be fresh; i t deteriorates upon standing and does not properly nitrate the paper. Allow the acid mixture to cool until the temperature is about 40 "C, which should take 25 to 30 min from the time of mixing. C a u t i o n : Coaling time can be shortened by using an ice bath, but special care must be taken to keep water away from the acid mixture. If the acid mixture is too warm, the paper scorches and turns to a pulpy mass. After testing with one paper to be sure the acid is cool enough. place four pieces of very drv paper, one a t a time, into i h e a c i d mixture. Any wet spots will not nitrate. Carefullv place a piece of paper on the surface of the acid mixture, then using a glasH rod push it gently beneath the liquid surface so that i t is covered with acid. I t should retain its shape. If the paper turns pulpy and loses its shape, the acids are too hot. The mixture is cooled a n additional five minutes before continuing. Repeat for each piece. Allow the papers to soak in the nitrating solution for 12 to 15 min. Properly nitrated papers will have a glassine-like appearance. Remove the papers using
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Distributed by D. Robbins &Company,Inc. Brooklyn, NY 11201.
Salts Used t o Create Colored-Flame Flash Papers Color
Salt
Green Orange Red-Orange Blue Yellow Violet
BaSOn CaS04 SrC03 CuBr NaCl KC1 or K N 0 3
clean forceps or a pair of glass rods and place them in a beaker of water to wash the excess acid away Allow them to stand for two minutes. As the papers soak i n water they will turn from brown-beige to off-white. After two minutes, place the entire beaker with the papers under running water for three minutes in such a way that the papers tumble vigorously Carefully remove the papers, allowing excessive water to drip off. At this point, the papers will no longer be glassine, but they will be opaque and not quite as flat a s the commercial papers, Caution: Dispose of acids by first neutralizing with sodium bicarbonate, then pouring down the sink drain with running water. The nitrated papers may be stored in an ethanol bath (nitrocelluose is insoluble in ethanol) or in a dessicator. Drying the Paper For flash paper that burns with a yellowish flame, nitrated papers may be used with no further treatment except for drying. Flash paper must be thoroughly dry to burn properly. Some trial and error is involved because sufficiently dry papers look and feel the same a s those not quite dry enough. Papers removed from the ethanol and dabbed with paper towel will take less than an hour to air dry Drying the papers i n a dessicator or in the oven takes a long time and is not very effective. Using a hair dryer reduces drying time to minutes for the small number (5 or 6 )of papers that are needed for one demonstration session. Caution :Hold the hair dryer close to, but not touching the flash paper, to avoid accidental ignition. Ethanol-soaked papers papers should be dry enough aft e r less than one minute. Properly dried papers (made from 5 x 10 cm sheets) weigh less than 0.2 g (between 0.15 and 0.17 is best). To avoid wasting nitrated paper, test a small piece t h a t appears dry to make sure i t burns instantly with no ash. If the papers are to be used the same day, store in paper towels, and redry them briefly with a hair dryer an hour before lighting. For papers that burn with colored flames, the nitrated papers are dried, then coated with salt to make coloredflame flash paper a s described in the next section. Procedure for Colored-Flame Papers Previous methods for making colored-flame flash papers soak them in aqueous solutions of salts that contain emitting species (1, 2, 4-6 ). However, i t is time-consuming to Volume 72 Number 12 December 1995
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dry the papers prepared in this way, particularly in the case of those soaked in solutions of hygroscopic salts such as chlorides of strontium and barium. A more convenient method to make colored-flame flash paper involves coating dry nitrated papers with powdered salts. The salts used here and the colors they produce are listed in the table. Caution: Do not substitute other salts without first checking their toxicity.
The most efficient way to do the salt coating is in a plastic bag partly-filled with the salt, ground if needed using a mortar and pestle. Papers are shaken for a minute or two with the salt until evenly coated. (Note that not enough salt adheres to the commercial papers to change their flame color from the original yellow.) Procedure for Multi-colored Flame Papers A (dry) paint brush dipped i n powdered salt can be used to coat a portion of a nitrated paper. Too much sodium chloride or strontium carbonate will produce overpowering yellow and red. Green i s masked easily, so apply the green to a larger area than other colors. A hair dryer can be used both to remove any excess salt and to redry papers.
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Journal of Chemical Education
Lighting the Paper The lighting technique determines the appearance of the flame. To prepare flash paper for lighting, leave whole or fold in fourths or fold in halves. Hold u p high , light in the middle of a fold and toss in the air when lighting. There should be a brief intense flame, a hissing or whooshing sound, and no ashes. The type of lightweight papers described here will dance in the air and are easily visible to a n audience. Caution: Be sure to keep the paper away from spectators. The lit paper may travel further than expected. Make sure there are no flammable solvents nearby, such as ethanol from a storage bath Literature Cited 1. Luoma. J. R.: Peyrer J. R.
J Chem Educ. 1988.65.452,
2. Thomas. N. C.; B m m . R. J. Chsm Educ 1992.69.328.
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3. Shakhashi", B. 2. Chemicol D~mondmlions:University of Wisconsin: Vol. 1 1983. p 43.
4. Conkling, John A. Chemistry of Pymtcehnier: Bade Principles and Theory; M . Dekker: New York. 1985. 5. Ragrds1e.R.
O.:Drismll. J A . J
Chem. Educ 1992.69.828.
6. Pearran, R. S. J Chem. Edue. 1985.62.822.
