In the 1920s chlorine gas was marketed as a treatment for cold, flu, whooping cough, etc. The patient would break open the Kil-a-cold chlorine "bomb" in a closed room. The 0.35g of chlorine gas would permeate the air the patient was breathing. Ads said their cold symptoms would disappear within an hour. Chlorine gas is toxic at high doses and had been used by the Germans in WWI before this treatment was marketed.