One of the men who received chemical burns in an anhydrous ammonia accident mid-month has died. 68-year-old Robert Ryan of De Witt died Monday at University Hospitals in Iowa City after a tank he and another worker were filling burst on April 15th at the River Valley Co-op near Calamus. A welded seam apparently failed. 23-year-old Nathan Nissen of Welton was also burned in the incident which is under investigation by state and federal authorities.