GRAHAM'S LAW OF DIFFUSION USING OVERHEAD PROJECTOR
(Aaen &dj
Submitted by: Paul Reber, John Adams High School, South Rend, Indiana Checked by: Julian R. Brandou, Michigan State University, East Lansing PREPARATION
Provide a glass t.ube, 10 mm i.d., 25 cm long, and open at hoth ends; two cot,ton swabs about 2 cm long and of a diameter to fit inside the t,ube; two rorks to fit t,he tube; a clear vinyl plastic rule 25 cm long; and aqueous solnt,ions (concentrated) of NH3 and HCI. DEMONSTRATION
Place the 25-cm rule on the plat,form of the overhead projector, adjacent and parallel to the tube. Dip one swab into the HCI solut.ion and the other swab in the NHI solution. Immediately place the swabs of cotton in opposit,eends of t,he tube and insert the corks. REMARKS
Observe the ring of XH&1 formed in approximately 60 seconds. Zote the position of the ring in relation to the markings on the 25-cm scale and compare data obtained with that predicted by Graham's Law.
Journol
01Chcmiool Edrcolion
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January 1361
DEMONSTRATION NOTES Frmn time lo lime ilents such as the Jollowng, u.hich do not require a fir11 haif-page, will be listed logelher. Some of them will be modzjicolions of previously published demaslralions, i n vhich cose il is suggested lhal they be clipped and attached to Ue perlinen1 eiperiment.
COLOR CHANGE WITH TEMPERATURE
BURNING PHOSPHORUS IN AIR
Roger Wheaton, demonstration-lect.ure assist,ant a t Michigan State University, observed that the residue remaining in the Soxhlet extraction apparatus after t,he completion of the chemical equilibrium experiment described by S. B. BUTLER ("Tested Demonst,ration," THIS JOURNAL, 37, November 1960) was quite temperat,ure sensitive. A similar solution can be prepared direct.1~ by mixing 20 ml of 0.5 M CoCL solution vith I6 ml of saturahed NaC1 solut,ion. When this mixture is chilled in cold water it t,urns pink and 'when heated for a brief time in the Bunsen burner flame v i l l turn blue. The process may be repeated at will.
Dr. H. K. Alyea, of Princeton University, suggest,s the use of a 3/8-in.flat head machine holt which has a small recess drilled in the end. This recess when filled with red phosphorus makes a free standing support for the phosphorus when demonstrating the removal of oxygen from the air. The holt may be placed head down in a shallow pall of water and a bottle may be lowered over t,he phosphorus once it is ignit,ed.
SUBLIMATION
Dale E. Rose, of Hampton High School, Virginia, suggest,s plunging a hot copper mire (fastened on t,he end of a wooden splint) into metaldehyde. The mat,erial sublimes readily and re-crystallizes in the air forming beautiful snow-like crystals. The met,aldehyde may be synthesized by cooling a mixture of acetaldehyde and a drop of sulfuric acid in an ice salt bath.
CATALYTIC OXIDATION OF AMMONIA
Clayton Berling of Oakland Cit,y College, California, points out that copper mire gauze is a very effective catalyst for the oxidation of NHs. The use of copper wire gauze in place of platinum or copper wire makes a more spect,acnlar demonstrat,ion, especially effective if the room can be darkened slightly. See: (References are to the 1960 Reprint Edition of "Tested Demonstrations") ALYEA, H. N., page 38, 135; STATE, H. M., page 61; NECHAMKIN,H., AND MCCLARN~N J. J., page 81.
