edited bv GEORGEL. GILBERT Denison University Granville. Ohio 43023
The Sunset Demonstration-A Variation
Spectroscopy Illustrated-A
S U B M I ~BY D
SUBMITTED BY
Jeffrey C. May
Erwin Boschmann
Lecture Experiment
709 Antrim Street Cambridge, MA 02139 BY CHECKE~
CHECKED BY
George Virtes
George Wollaston
Ward Melville High School Setauket. NY 11733
Clarion State College Clarion. PA
Two classical demonstrations have been used to illustrate the scattering of sunlinht wassine through the atmos~bereat sunset. In the first, a s k i 1 amount of ;ilk is added to water through which a beam of linht is shining. The beam can be viewed directly, or its light can he cast on a screen. The colloidal fat and urotein uarticles scatter blue light - and the beam is blue. The source appears to be red. In the other demonstration, colloidal sulfur is produced in situ by the addition of sulfuric acid to a solution of sodium thiosulfate. The results are similar t o the first demonstration: however, the process is more dramatic in that the sulfur mixture undergoes progressively more scattering as the number and size of colloidal particles increases. Eventually, the light source as viewed through the mixture reddens and dims until it is obliterated. In the present demonstration, only a stack of about 20 sheets of white paper are needed. No solutions are necessary. A lamp such~asagoose neck serves as an excellent light source. The lamo is adiusted so that it ooints toward the audience. and the stack oipaper held oveithe lamp so that the sheets, when released, fall one by one over the hulb and cover it. T o avoid initial glare, the first sheet should rest over and cover the hulb before the lamo is lit. '1'0 .er the -;lma.l tvtiwt, tht lirht.i in 1111 n,
