28 
liquid, POM es about 36°. Its molecular formula is C; Hs, and it —— 
mide, C; Hg prac but nó metallic derivatives like 3 
the two Mis EET of Aoc Ap 
* Bouchardat (Compt. rend. di 81, p. 654, and. vol. 89, pp. 261 
and 1117) observed that when isoprene is heated to a iemperature 
near 300°, it gradually polymerises into a terpene, which he called 
diisoprene, b but which is now called dipentene. This compound — 
: 1 ; 
is ad 1 a to uh elastic solid, Which hai een Bee 
by G. "geb enda and by myself. Tt appears to be true india- 
rubber 
K Specimens of isoprene were made from several terpenes in the 
eourse of my work on those compounds, and some of nm 
I have preserved. I was surprised a few weeks ago at finding the — 
contents of the ido containing isoprene from turpentine 
entirely changed in appearance. In place of a limpid colourless | 
liquid, the bottle contained a dense syrup in which was floating 
seve voral large masses of a solid of a sites nb Slade Upon g 
pbi. 
be 
that a small quantity of acetic or formic acid had been produce 
by the oxidising action of the air, and that the presence of this 
compound had been the means of transforming the rest. 
liquid was acid to test paper, and yielded a small portion of | 
unchanged isoprene. 
*'lhe artificial india-rubber, like natural rubber, appears to 
consist of two substances, one of which is more soluble in 
benzene or carbon bisulphide than the other 
eo 
“The artificial dans unites with sulphur in the same way 4 
ordinary rubber, forming a tough elastic compoun 
* The constitutional formula of i isoprene is now known to be :— 
xs hese iat lene, CH, = CCH; — CH = CH;. 
“It obvious that compounds such as these, or 
Johi inkad carbon, may polymerise in a variety of ways; and 
in the present condition of our know ledge even of oorh it 
would be idle to speculate as to which out of the numero 
possible arrangements would cor arene to the constitution ©) 
caoutchouc.” —(Proc. Birm. Phil. Soc. viii., Pt. 1.) 
In a recent letter Professor Tilden states :—* As you may 
imagine, I have tried everything I can think of as likely to 
promote this change, but withoat success. The polymerisation 
etre slowly, occupying, according to my experience, 
veral years, and all attempts to hurry it result in the produc 
ton not of rubber but of ‘colophene,’ a thick sticky oil q ut 
useless for all the purposes to which rubber is applied." 
