Abstract: A volatile anesthetic vaporizing apparatus including a concentration control flow valve means actuated by a substantially linear rotary dial for dividing an inflowing gas stream into two separate streams, one stream being passed over liquid anesthetic to pick up a vapor and the other stream flowing through a bypass duct. The gas stream flowing over liquid anesthetic flows through a temperature responsive valve means, the latter being actuated by a temperature sensitive bimetallic strip which is in direct contact with the vapor saturated air stream which is relatively cool due to the vaporization of the liquid anesthetic. The valve means so situated in the vapor stream essentially does not include any moving parts. Such valve means is formed by the spaced mounting of a planar valve element on a planar surface having a vapor opening therein or an inlet passage.