Three colour change sealed glass tubes, supplied by SKC Ltd, England, and made by Gastec Corporation, Ayase-Shi, Kanagawa prefecture, Kanto, Japan, 1996-1999. Used with gas sampler to give an on-the-spot reading, either after a fixed volume of air has been drawn through the tube, or gradually over time with exposure. Colour change tubes for air change sampler, 1996-1999 1996-1999