A highly reliable bulk chemical delivery system for high purity chemicals employing a manifold that ensures contamination free operation and canister change outs with a minimum of valves and tubing. A cylinder head closes of a combustion chamber in the cylinder interior. The lens is composed of six different optical units surrounded by Fresnel rings. The protruded electrode on the component-side electrode terminal in the predetermined position is higher than the protruded electrode on the component-side electrode terminal in a different position from the predetermined position. A window is disposed in the front panel of the subunit housing and is positioned to provide a view of the plurality of line connectors. A polyisocyanate mixture comprising polyisocyanate A represented by the following general formula : 1wherein, R is an alkylene group having 2 to 5 carbon atoms, n is 1 or 2 and m is 0 or 1; and polyisocyanate B derived from one or more types of aliphatic or alicyclic diisocyanates, substantially free from monomeric diisocyanate and having a number average molecular weight not higher than 750.