I would like to know the name of an old si-fi movie I seen on t.v. in the seventies?

I saw a movie on crecher feature were these aleons come to a small town in a flying saucer they took people from the town onto their ship and replaced them with copies. The movie was simular to invation of the body snachers but when the aleons died they would desolve into soapbubbles. I believe it was a very old movie because they didn't use blood.