A chocolate factory at work, Liebig trade card, early 20th century.

FRANCE - MAY 19: No 5 in the 'Chocolat' (Chocolate) set of trade cards produced by Liebig, showing workers in a chocolate factory engaged in various stages of the manufacturing process. The Liebig company produced sets of trade cards to promote their meat extract, a cheap and nutritious product invented in 1847 by chemist, Justus von Liebig. The meat extract was produced from 1865 at the Fray Bentos-Liebig processing plant set up in Uruguay. 1,863 sets of cards were produced continuously from 1872 until 1975 by which time the company had joined with Brooke Bond to become Brooke-Bond Oxo and was owned by Unilever. (Photo by SSPL/Getty Images)