493 SCIENCE PROGRESS 



decomposition, is apparent when the distillate is examined, for 

 although the distillation does not commence until a temperature 

 of about 160 C. has been attained in the flask, yet some portions 

 of the distillate are found to have boiling points below 40 C. 

 The indiarubber molecule has evidently suffered disruption, 

 and, in the process, smaller molecules have been produced. 

 Now, although it does not follow that in the decomposition 

 products one is likely to find exactly the same arrangement 

 of carbon atoms as in the parent substance, yet one might 

 reasonably expect that an examination of the constitution of 

 these products would yield some clue to the probable constitu- 

 tion of the indiarubber molecule. Therefore it is not surprising 

 to find that, baffled probably by the complexity of the caoutchouc 

 molecule itself, chemists have, in the past, chiefly turned their 

 attention to a study of these products of destructive distillation. 

 It would take too long to refer, in chronological order, to the 

 whole of these investigations ; for such an account the reader 

 is referred to the author's report on this subject in the British 

 Association Reports, York, 1906. It will be sufficient to consider 

 the constitution of the compounds which have from time to 

 time been isolated from the mixture which is obtained on 

 distillation. 



Isoprene, C 6 H 8 , Boiling Point 37 — 38° C, Specific Gravity '682 



Most of the earlier investigators observed the presence of a 

 low-boiling portion in the distillate, but the separation of a single 

 definite substance was not at first effected. W. H. Barnard 1 in 

 1833, Beale and Enderby 2 in 1834, John Dalton 3 (1834), Dr. 

 Gregory 4 (1835 or '36), and Liebig 5 (1835) all obtained fractions 

 boiling between 32 and yy° C. A. F. C. Himly 6 in 1835 described 

 an oil b.p. 33 — 44 C, and A. Bouchardat 7 (1837) was aD l e t0 

 separate two fractions of the distillate, both of which were stated 

 to boil below 20° C. 



To Greville Williams 8 (i860), however, belongs the credit of 



1 Dr. Ure's Dictionary of Arts, etc., 1853, p. 358. 



2 Ulnstitut, 1834, p. 290. 



3 London and Edin. Phil. Mag. and Jonrn. of Science, 1836, p. 479. 



4 Ibid. p. 322. 



5 Anjialen der Chim. u. PJiarm. 1835. 



6 Dissertation, Gottingen, 1835. 



7 Jonrn. de Pharm. vol. xxiii. 1837. 



8 Proc. Royal Society, i860, p. 517. 



