edited bv
tested demonstrations The Bird-Scarer (Combustion) Demo Rubin att ti no' and James D. Arehart Wright State University Dayion, OH 45435 Neville W. Foot and James 6. Stott Department of Chemical and Process Engineering University of Canterbury Christchurch 1, New Zealand
While on leave in New Zealand one of the authors (RBI came across an intriguing device used by orchardists to scare birds. The original device used acetylene gas, but modern ones use LPG. Via an intricate mechanical system a measured amount of a fneVair mixture flows into a combustion chamber where it is ignited by a piezoelectric lighter. The bangs are very loud, occur at fixed intervals, and do scare birds. The device described in this paper is the result of simplifying the costly commercial device ($1000) to demonstration scale. The loudness and freqnency of the explosions are adjustable.
64
Journal of Chemical Education
Granville, OH 43023
The long-reach spark plug is mounted 6 in. from the end of the large tube. An insert threaded internally to accept the spark plug and externally to accept a lock nut is 1-in. long. This arrangement permits the spark to be adjusted from about 318-U8 in. from the edge of the insert to provide a variable length diffusion path. A lock nut on the outside keeps the spark plug in place after adjustment. See the figure for details of the assemblies. The bird-scarer must first be adjusted (after assembly) for the proper airlfuel mixture. The fuel may be natural gas, methane, propane, butane, or LPG. With no electrical connections made the gas is turned on and the air intake of the Bunsen burner and the fuel flow are adjusted so that a 1.5-2411. pale blue flame bums above tlie outlet tube. Note the flow settings and turn the gas off. h the gas burns back into the tube there may be an explosion. If there is no explosion, then ignite the remaining mixture in the tube by holding a long
Description of Device The bird-scarer is shown in the figure. I t is fabricated from a 12-in. length of 4-in. steel or copper tubing or pipe. The top and bottom plates are held in place with three screws and are keyed for easy assembly. These plates are screwed into the main tube for ease of assembly and for access for fastening the spark plug in place. The screws are more than adequate to hold the plates in place during operation. The top plate has a 2-in. length of 1-in. tubing weldedbrazed on as the outlet. The bottom plate has two assemblies attached. The one inside the chamber has a 3in. diameter plate positioned on spacers 1 in. above the central opening to serve as a deflectorto minimize streaming. A 1.5-in. diameter solid cylinder that is 1.5-in. long is attached to the bottom of the bottom plate and has a hole drilled through centrally to accommodate the end of a standard Bunsen burner. A thumb screw holds the burner in place. Just past the burner tip four 114-in. holes are drilled through from the side to serve as a n additional air supply to that of the burner itself. These holes are sealed with small corks or threaded plugs.
' Author to whom correspondence should be addressed.
GEORGEL. GILBERT Denison University
Construction diagram for the bird-scarrer.
match over the outlet. Some experimenting with the gas flow rate, the position of the spark plug, and the amount of supplemental air (using the corks or threaded plugs) will be necessary to "tune" the apparatus for the loudest bang and the periodicity of the bangs. The spark plug is connected to a 7,000-10,000V low current source using a standard spark plug cap and being sure to mound the source to the oioe. Transformers used for neon displays are a convenient source for the necessary high voltage. For maximum safety, be sure that the wiring includes a n onloff switch, a visual indicator of power, and a solenoid valve on the fuel line that shuts off the gas flow when there is no current. After connecting eve&hing, turn on the gas and the power. Explosions will occur every 10-15 s depending on the diffision time delay which is, of course, adjustable. You can get bigger bangs by placing a resonator tube above the outlet and tuning it for loudness. The entire apparatus may be mounted on a large ringstand using three-fmger clamps. Running the bird-scarer in the dark provides nice visual effects. Both the gas flow and the spark plug run continuously while the device is in operation. The device can be used safely for systematic studies of explosion limits for gas mixtures.
..
-
Caution: rhe explasiunv are loud and the pipe gets hot after runnmg for a feu rninnrcs. This dmmn should br run only for a few minuw,. Always be sure to test explode any gas remaining in the pipe.
Syringe Gas Generators Hubert N. Alyea Frick Chemical Laboratory Princeton, NJ 08540
Poisonous gases can be generated safely in a plastic syringe without their escaping into the classroom. The syringe may be passed around for individual student inspection. Directions for two different size gas-generating syringes are given below. The 5 m L Syringe Generator Teacher Pre-test
Determine what volume of liquid reagent is required to cenerate 4 mL of eas from 1mL of solid. (Let us assume that 8 drops of ~ ~ 7 1mL ~ of1granular ~ s F ~ give S 4 mL of H2S gas.) Student Procedure Pour 1 mL FeS plus exactly 8 drops of HCI in the test tube (Fiz. 1).Immediately attach the pas - collector assembly consifitin(: of ;i stopp& plus a 3-cm coppcr tubing plus a 3-cm plastic tuhing fitted over the nozzle ofa 5-mL d a s tic syringe with itsplunger fully inserted. When the syringe becomes four-fifths full of H2S gas, disconnect the test tube and, f o r safety, immediately s u b m e r g e t h e test t u b e a n d reagents i n t o a pail of water. Stopper the syringe with the rubber bulb from a medicine dropper. The 2-02 Syringe Generator Device 1
Use a 2-02 (60-mL) plastic syringe and follow the procedure given above. Device 2 See Figure 2. Cut slight grooves on the face and one side of a plastic cap that fits loosely into a 2-02 syringe. The
Figure 1. (lefl)The 5-mLsyringe. Figure 2. (right)The 2-02 syringe created by method 2 grooves will permit the escape of gases. Close the syringe nozzle with a stopper or rubber bulb. Into the cap put enough reagent to generate 50 mL of gas. Drop the cap into the syringe, and immediately fully insert the plunger. As gas generates, the plunger will move outward. When the syringe is almost full of gas, join its nozzle, using a 5-cm length of rubber tubing to a second 2-02 syringe with its stopper fully inserted. Push in the plunger, forcing the gas into the second empty) 2-02 syringe. Storage of Gases
There is no longer a need for gas bottles! Prepare 2-02 syringe samples of gases listed in the table below. Store them submerged in a bucket of water in a locked area outside the laboratory. Preparation and Identificationof Gases
Gas
Reagents
Identification
deep blue with cu2* HCI + NaOH pellets turns limewater milky water + Alka-Seltzer turns limewater milky HCl + gran. Zn exploded by a burning match cations ppt colored Hydrogen sulfide, HCI + FeS H2S sulfides forms brown NO2 Nitrous oxide, NO dil. H 0 3 + Cu in air . Hz02 + MnOe makes a burning Oxygen, 0 2 splint glow Sulfurdioxide. SO2 HCI + NaHS03 bleaches dyes-aq turns violet M n 0 4 . into colorless MnL+ turns orange ~r20?Into green CPt Re Nitrous Oxide. NO. Allow gas to purge out air, momentarily, before insening plunger. Resulting clear NO forms brown N@ when air is admined. See R. J. Wojt, J. Chem. Educ 1987, 4, 1052. Also, H. N. Alyea, Syringe gas generator for poisonous gases, Teachers Handbook for Armchair Chemistry.1984, p. 46. Ammonia, NH3 Carbon dioxide, COe Hydrogen. HZ
Volume 69 Number 1 January 1992
65
