An iodine pentoxide (Hoolamite) test consists of a glass tube filled with a reagent mixed with fuming sulfuric acid and carried by crushed pumice through which a known volume 1638 of the air to be sampled is discharged from a rubber bulb after preliminary drying. The bulb is squeezed 10 times; the carbon monoxide present changes the color of the reagent from grey to green, and the concentration is obtained by reference to a color chart supplied with the instrument. The instrument reads down to about 0.07% carbon monoxide.