The Kjeldahl digestion rack, designed to determine protein, nitrogen and ammonia content of organic compounds, was developed by the Danish chemist, Johan Gustav Christoffer Thorsager Kjeldahl (1849–1900). A tag on this example reads in part “MODERN SCIENTIFIC RESEARCH AND / PRODUCTION CONTROL EQUIPMENT / ENGINEERED AND BUILT BY THE / PRECISION SCIENTIFIC CO. / Made in U.S.A. CHICAGO, ILLINOIS.”