Use pliers to carefully snip the glass tips off each end of the glass sampling tubes, facilitating attachment to the flexible plastic tubing and subsequent insertion of carbon dioxide into the glass sampling tubes.
Push the plunger on the syringe all the way down to clear any residual air. Pull the plunger back to collect 100 cc of air. In a greenhouse, test air in the immediate area around growing plants. When testing indoor air, which tends to be circulated, take air samples throughout the room, depending on how many test kits you have at hand.
Insert the syringe into the flexible plastic tubing, and place the tubing over one of the holes at the end of your glass tube. Push the air from the syringe into the glass tube. The white powder in the tube will turn red or blue, depending on the manufacturer, in response to the carbon dioxide. Determine the amount of carbon dioxide in the tube by reading the level of the colored indicator powder (where the color stops and the powder returns to white) on the side of the glass tube in parts per million.