Pure chloroform is known to be decomposed readily in the presence of air, even in the dark, although then very slowly, but in the absence of oxygen. In the first stage of the decomposition, chloroform produces an intermediate peroxide, Cl₃COOH, which disapears in the second stage to yield chlorine, phosgene, and hydrochloric acid through two courses (a) and (b) as illustrated in chart 1.-1 The mechanism of phosgene formation was evidenced by the fact that decomposed chloroform produced diphenylurea by reaction with aniline and the reaction of the decomposed trichloroethylene or tetrachloroethane with aniline produced the same dichloroacetanilide, as shown in chart 1.-2 and 3 Ethanol added to the decomposed chloroform showed apparently a catalytic effect decomposing the peroxide to Cl₂ or COCl₂ through the courses shown by chart 1.-1-a and b Alcohols except methanol, ethers except dioxane, phenols, and hydrocarbons were useful as a stabilizer for chloroform, while acetone, acetic acid, ethyl acetate, and benzene were useless. In alcohols, the stabilizing effect became stronger with increasing number of carbon atoms in the molecule. It is interesting that hydrocarbons such as hexane and decane possess a marked effect as a stabi1izer. It is difficult to understand how the presence of so small an amount of stabilizer could prevent the decomposition of chloroform but it may not be unreasonable to assume the following : 1) It is considered that the stabilizers prevent the decomposition of chloroform in its primary stage, by the fact that a small amount or the stabilizer prevents the formation of even a trace of Cl^- under conditions most favorable to decomposition : 2) The stabilizers containing hydrocarbons act as an anticatalyst in unchanged form, because they are so resistant to chemical change : and 3) The fact that various substances of different types such as alcohols, ethers, phenols, and hydrocarbons are useful as a stabilizer shows that the mechanism of this stabilization is not simple.