Abstract: An apparatus for the continuous treatment of an advancing web such as a cotton fabric with one or more reactive gases comprises one or more reaction chambers, each including fluid dicharge means for directing a treating gas onto the web in the chamber and evacuation means disposed on both ends of the chamber to prevent both the fluid from escaping from the chamber and the fluid outside the chamber from entering the chamber. Heating means adapted to heat the continuously advancing web of fabric material may also be provided, if desired.Such an apparatus may be used for the application of gases such as ammonia to a fabric impregnated with monomeric tris (hydroxymethyl) phosphine to form on the fabric a polymerized phosphorus-containing material and to impart flameproofing properties thereto. The apparatus can also be used to apply gases such as formaldehyde or sulfur dioxide or both to a cellulose fiber-containing fabric at an elevated temperature and in the presence of controlled amounts of moisture.