. . . . "Also, we may use metal derivatives, classified herein as salts, having the formula M(OR),,, wherein M represents the polyvalent metal, R is an alkyl or aryl radical, and n is the valence of M, for example, Ti(OC H Ti(OC H Ti(OC H tetra-Z-ethylhexyl titanate, tetrastearyl titanate, tetraphenyl zirconate and the like, for example, the metal derivatives of the enol forms of acetylacetone, acetoacetic" . .