254 
ME. C. GEEVILLE WILLIi3IS ON ISOPEENE AND CAOnCHINE. 
in phials of the juice, with the annexed results. They were dried at 100°. The first 
specimen was dark brown, the second pale straw-coloured and almost transparent. 
I. 0'2010 grm. gave 0‘6346 carbonic acid and 0‘2230 water. 
II. 0T972 grm. gave 0‘6252 carbonic acid and 0-2134 water. 
III. 0-6958 grm. gave 0-0064 of brilliantly white ash. 
Or, per cent., — 
Experiment, 
A 
Faeadat. 
Carbon 
86-1 
86-5 
87-2 
Hydrogen 
12-3 
12-0 
12-8 
Ash 
0-9 
Nitrogen, oxygen, and loss 
0-7 
100-0 
My specimens were probably less pure than that analysed by Faeadat. 
I am anxious to call attention to the fact that the atomic constitution of caoutchouc 
appears to bear some simple relation to the hych-ocarbons resulting from its decompo- 
sition by heat. The composition of caoutchouc coincides with that of isoprene and 
caoutchine, as found by analysis, to a degree which is remarkable when we consider that 
caoutchouc, in addition to being non-crystalline, is scarcely capable of purification by 
chemical means. Additional evidence may be found in the smallness of the residue 
which is left on submitting caoutchouc to heat. The following results of the analyses 
will show the amount of confidence which may be placed in this idea. 
Isoprene. 
Mean, 
Carbon . . 88-0 
Hydrogen . 12-1 
Caoutcliine. 
Mean. Faeadat, 
88-1 87-2 
12-0 12-8 
Caoutcliouc. 
A ^ 
C. G. M'.* 
86-9 87-3 
12-4 12-1 
The following Table contains a summary of the physical properties of isoprene and 
caoutchine. • 
Table of the Physical Properties of Isoprene and Caoutchine. 
Vapour- 
densitv. 1 
Name. 
Formula. 
Boiling-point. 
Specific graritr. 
1 
1 
Experiment. 
Calculation. 1 
Isoprene 
CIO 
0 
37 
0-6823 at 20 
2-44 
1 
2-349 ' 
Caoutchine 
COO J|16 
171 
0-8420 
4-65 
4-699 ' 
It will be seen from what has been said upon the composition of the above bodies, 
that they may equally be obtained from caoutchouc or gutta percha. When the latter 
substance is submitted to careful distillation, the phenomena are essentially the same as 
with the former. The distillate contains a small quantity of water, which, instead of 
* Asti deducted. 
