Another purifier of water is ozone. Great claims have been made for ozone as a germicidal agent for water in the last few years, and many forms of apparatus for generating and using it have been applied. The schemes for promoting the use of ozone are hard to dissociate from commercial exploitation. Ozone undoubtedly has the power to destroy the life of pathogenic organisms if it can be brought into contact with them. The inefficiency of the ozone generators and the difficulty of thoroughly bringing ozone into contact with the germs to be destroyed are practical objections to the general use of this reagent. It also is evidently very much more expensive than the simple treatment with hypochlorite, which remains today the most efficient and most economical method of chemically treating water for germicidal purposes. Violet rays, radiant emanations and other forces of a mysterious or little understood character, have also been recommended for the sterilization of water. These recommendations have only an academic value, inasmuch as their efficiency has not been demonstrated in a practical way.