How can I tell if my soda lime is working and still scrubbing CO2?

Soda lime does have a PH-sensitive Ethyl Violet color change indicator, but this is weak and typically does not change color strongly even though the soda lime has lost strength. Adsorption of CO2 by soda lime requires moisture, so if the soda lime has dried out this will reduce scrubbing capabilities. You can test your soda lime by connecting it to the CI-340 intake. Start a measurement in Single Channel Absolute mode (S) so you are simply reading the CO2IN value. Blow into the tubing going into the soda lime column and watch the CO2IN reading on the CI-340 to see if it increases. There will be a lag time while the sample from your breath travels through the soda lime and tubing to the CO2 IRGA sensor. If the CO2 IN rises, the soda lime is probably exhausted and needs replacement. To refresh soda lime, try adding a small amount of water to the bottom of the soda lime/desiccant column. You should not add more than 5 cc of water at a time. Be sure to replace the cotton filter at either end of the plastic column of soda lime. Repeat the breath test to see if the soda lime improves at scrubbing CO2. If not, replace the soda lime with fresh and test again.