Kekulé, August (1866). Lehrbuch der organischen Chemie [Textbook of organic chemistry] (in German). Vol. 2nd vol. Erlangen, (Germany): Ferdinand Enke. p. 463.{{cite book}}: CS1 maint: unrecognized language (link)
Watts, Henry, A Dicitonary of Chemistry and the Allied Branches of Other Sciences (London, England: Longmans, Green, and Co., 1863), vol. 1, "Camphorone", p. 733.