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 cur- rent 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 an 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 ring- stand 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 sy- ringe without their escaping into the classroom. The sy- ringe may be passed around for individual student inspec- tion. Directions for two different size gas-generating syringes are given below.

The 5mL Syringe Generator Teacher Pre-test

Determine what volume of liquid reagent is required to cenerate 4 mL of eas from 1 mL of solid. (Let us assume that 8 drops of ~ ~ 7 ~ 1 ~ s 1 mL of granular F ~ S give 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 assem- - bly consifitin(: of ;i stopp& plus a 3-cm coppcr tubing plus a 3-cm plastic tuhing fitted over the nozzle ofa 5-mL das - tic syringe with itsplunger fully inserted. When the sy- ringe becomes four-fifths full of H2S gas, disconnect the test tube and, fo r safety, immediately submerge t h e test t ube a n d reagents in to 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 proce- dure 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-mL syringe. 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 out- side the laboratory.

Preparation and Identification of Gases

Gas Reagents Identification

Ammonia, NH3 deep blue with cu2* Carbon dioxide, HCI + NaOH pellets turns limewater milky

COe water + Alka-Seltzer turns limewater milky Hydrogen. HZ HCl + gran. Zn exploded by a

burning match Hydrogen sulfide, HCI + FeS cations ppt colored

H2S sulfides Nitrous oxide, NO dil. H 0 3 + Cu forms brown NO2

in air Oxygen, 0 2 . Hz02 + MnOe makes a burning

splint glow Sulfur dioxide. 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.

Volume 69 Number 1 January 1992 65