Ingold, Sir Christopher, (1893-1970), an English chemist, made fundamental contributions to the field of organic chemistry, the study of compounds that contain carbon atoms. Often in collaboration with his chemist wife, Edith Hilda Usherwood, he investigated the electric charges present in organic compounds and developed theories on the part these charges play in chemical reactions. He and the Welsh chemist Edward David Hughes carried out detailed studies of elimination reactions, in which molecules lose a portion of their structure, and substitution reactions, in which one subunit of a molecule is replaced by a different one.