Heinz Mustard Gas October 2008, Cervera de los Montes and Pittsburgh Ø 6 x 20 cm Full custom Heinz Tomato Ketchup bottle i Heinz Tomato Ketchup is the best selling condiment in the United States. Mustard gas is a vesicant chemical warfare agent with the ability to form large blisters on exposed skin. It is yellow-brown in color and have an odor resembling mustard. Mustard gas was first used effectively in World War I by the German army against British soldiers. The United States has mustard gas stockpiles located in Alabama, Arkansas, Colorado, Indiana, Kentucky, Oregon and Utah.