How to Monitor the Oxygen Percent in Air
- 1). Tear off a ball of steel wool about an inch in diameter and lodge it at the bottom of the test tube. Add a little vinegar or soapy water and vigorously rinse the interior, then drain the liquid, making sure the steel wool remains lodged at the bottom of the test tube.
- 2). Turn the test tube upside down. Immerse it in the glass of water. Air will be trapped in the test tube. Mark the initial level to which the water in the inverted tube. Store it in a place where it will not be bumped or jarred.
- 3). Check how far the water has risen into the tube after two days. Keep the mouth of the tube submerged so that no water escapes as you mark the level to which the water has risen. Check and mark the tube each day or two until the water ceases to rise, which usually takes about a week. The water rises to replace the oxygen depleted in oxidizing the steel wool. Once it stops rising, the oxygen is entirely depleted from the sample.You may remove the tube from the glass of water after the final marking.
- 4). Subtract the volume of the tube at the final marking from the initial volume. If you do not know how to calculate the volume of a cylinder, simply fill the tube with water and pour it into a measuring cup or graduated cylinder. Do the same with the tube filled only to the final marking in a separate measuring cup.
- 5). Divide the difference by the initial volume of the tube and multiply by 100. The result is the percentage of oxygen in the air sample you isolated.
