The Limonene Group of Ter penes. 
319 
a molecule of hydrocarbon can combine with but one molecule of hydro¬ 
gen chloride, he comes to the conclusion that the molecule of limonene, 
resp. dipentene is but half as large as that of pinene. 
Blanchet and Sell 2 (1833) obtained independently the same results and 
come to the very same conclusions. 
In 1835 Himly 3 obtained from the products of dry distillation of 
caoutchouc a fraction 168-171°. Saturated with hydrogen chloride this 
yielded “ salysaures Kautschen,” (dipentene dihydrochloride) from which 
the hydrocarbon can be regenerated by distillation with caustic potassa 
and rectification over metallic potassium. The regenerated hydrocarbon 
was colorless, possessed a limonene odor; spec, gravity 0.8423 at 16°; 
boiling point 171°; vapor density 4.461. He assigns to it the formula 
C 5 H 8 . 
An observation of Soubeiran and Captain (1840) is of great interest, 
viz.: that the hydrocarbon regenerated from the optically inactive 
“camphre de citron” (dipentene dihydrochloride) is likewise optically 
inactive and is thus distinguished from the “essence de citron” 
(+ limonene). 
Schweizer, 5 however (1840), still regarded the dipentene regenerated 
from the dihydrochloride as identical with the “carvene” (+ limonene) 
from which the dihydrochloride had been prepared. 
In 1848 List 19 observed that when the “ chlorwasserstoff verbindung 
des Terpins ” (dipentene dihydrochloride) is distilled with caustic lime, 
or when anhydrous terpin is distilled repeatedly with anhydrous phos¬ 
phoric acid a volatile oil of the composition “ C 20 H 16 ” is formed. 
In the following year (1849) Deville 20 regenerated the hydrocarbon 
from the “camphre de citron” (dipentene dihydrochloride) prepared 
from terpin hydrate and declares this hydrocarbon dipentene to be 
identical with “1’essence de citron” (+ limonene). This, he states, “fur¬ 
nishes the means to transform the essence of turpentine into the essence 
of lemon.” (That Deville, who made considerable use of the polariscope 
in his investigations, apparently gives no heed to optical properties in 
this case is rather surprising.) 
In 1860 Greville Williams 8 in his researches on “Isoprene and Caout- 
chine,” confirms Himly’s analysis. He states further that “ caoutchine” 
(dipentene) decolorizes four equivalents of bromine; that by the alter¬ 
nating action of bromine and sodium cymol is obtained, which upon 
oxidation yields “ insolinic acid.” Sulphuric acid converts “ caoutch¬ 
ine” into a viscid oil. Small quantities of an acid “C 20 H 16 S 3 O 6 ” are 
also formed from which a calcium salt, “ C 30 H 15 CaS 2 O 6 ” was made. 
Williams assumes that the heat effects a tearing assunder of a polymeric 
body (caoutchouc), and that the substances which are formed stand in a 
simple relation to the mother substance. 
Tilden 11 in 1882 repeated some of the experiments of Greville Wil- 
