Recent publications by Heath and Semon2 and by Bauser, Gibson and Pope2 make it desirable to publish an extension of work previously done in this laboratory.4Bv passing ethylene into a solution of selenium monochloride, Heath and Semon obtained a white crystalline compound melting at 118°, which they have described as symmetrical tetrachloro-diethyl selenide. Bauser, Gibson and Pope by the same reaction obtained the crystalline compound melting at 122°, and have described it as /3,/3'-dichloro-diethyl selenide dichloride. Upon reducing this substance in water solution with sulfur dioxide they obtained /3,/T-dichloro-diethyl selenide as a colorless oil which solidified when cooled. Basing their conclusions upon the nature of the products formed and upon the amount of selenium recovered these authors have represented the absorption of ethylene as follows.2CíH4 + 2Se2Cl2 = (ClC,H4j2SeCl2 + 3Se. Upon extending this reaction to the higher olefins, we have been able to show that the equation given above is the summation of two perfectly definite but consecutive reactions.2C>H4 + Se>Clo = (ClC2H4).,Se + Se (1) (ClC2H4)2Se + SesCls = (ClC2H4)_,SeCl., + 2Se(2) Bv passing the olefin into the selenium monochloride as the workers mentioned above have done, the ideal conditions for completing both stages are obtained. The action may be stopped at the end of the first stage by the simple process of reversing the order of bringing together the reagents.