318 
Wisconsin Academy of Sciences , Arts and Letters . 
Dipentene. 
Citrene 1 —J. Dumas, 1833. 
Citronyl 2 — Blanchet and Sell, 1833. 
Kautschin 3 — Himly, 1835. 
Citrene 4 — Soubeiran and Captain, 1840. 
Carven 5 — Schweizer, 1840. 
Cynen 6 — Volckel, 1854. 
Cinseben 7 — Hirzel, 1854. 
Caoutchine 8 — Williams, 1860. 
Cynen 9 — Grsebe, 1872. 
Isoterebenthene 10 — J. Riban, 1874. 
Di-isoprene 11 — Bouchardat. 
Terpilene 11 — Bouchardat. 
Dipentene 12 — ") 
i 
Terpene 12 —- }■ Tilden. 
Terpilene — J 
Citrene 13 — Watts, 1886. 
Cynen 14 — Wallach, 1884. 
Cajeputen 15 — Wallach. 
Cinen 16 — Wallach, 1884. 
Dipenten 17 — Wallach, 1884. 
In an article “ Sur la combinaison de l’essence de citron avec l’acide 
muriatique,” Saussure 18 (1820) states that from the “muriate citre” (dipen¬ 
tene dihydrochloride) the hydrochloric acid can be removed in part by 
distillation with caustic lime. 
In 1833 J. Dumas reports on the regeneration of the hydrocarbon 
“citrene” (dipentene) from the “camphre de citron” (dipentene 
dihydrochloride) by repeated distillation with caustic potassa and 
caustic baryta. He assigns to the regenerated hydrocarbon the formula 
C 6 H 4 and makes about it the following concluding remark: Si ’1 est 
done certain, que cette matiere, qui fait presque totalite de l’essence de 
citron, est isomerique avec celle, qui forme de son cote la presque totalite 
de l’essence de terebenthine, avec cette difference, que la condensation 
des elements est double dans la derniere.” Prom these remarks it be¬ 
comes quite evident: 
1. That Dumas recognizes the isomerism between pinene and limo- 
nene, resp. dipentene. 
2. He supposes the limonene present in the oil of lemon to be identi¬ 
cal with the dipentene regenerated from the dipentene dihydrochloride 
obtained by the addition of hydrogenchloride to, and by the inversion of 
limonene. 
3. He recognizes the fact that limonene will, absorb again as much 
hydrogenchloride as pinene. Laboring under the false supposition that 
