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LXXXIX. Observations on certain Liquids obtained front 

 Caoutchouc by Distillation. By John Dalton, D.C.L., 

 F.R.S., ^x* 



Manchester, November 10, 1836. 



T"^R. GREGORY having published in the last number of the 

 -*-^ Philosophical Magazine (p. 321.) some interesting experi- 

 ments and observations on the liquid obtained by the distilla- 

 tion of caoutchouc, 1 have thought it would be acceptable to 

 that gentleman, as well as to the public, to be made acquainted 

 with the results I obtained from the same subject about two 

 years and a half since, more especially as my experiments 

 chiefly tend to establish additional properties to those de- 

 duced in Dr. Gregory's essay. For this purpose I send the 

 Editors a copy of my paper read before the Literary and Phi- 

 losophical Society of Manchester, on the 17th of October, 

 ISS*, which has not been published. I think it is obvious 

 from what follows that most or all the varieties of vegetable 

 combustible products of the oily character must be constituted 

 of central atoms of carbon, oxygen, or carbonic oxide, along 

 with a number of atoms of binolefiant gas, placed alternately 

 around the central atom ; and that the repeated distillation of 

 them, at first with a greater and then with a less heat, gra- 

 dually attenuates the compound atom, till at last it becomes 

 one or two atoms of binolefiant gas slightly adhering to the less 

 volatile parts of the oil, so that the gas, when not under suf- 

 ficient restraint, expands into the atmosphere at the ordinary 

 temperature. 



Observations, Sj-c. Read October 17, 1834. 



The article caoutchouc is too generally known to require 

 a particular description ; it may suffice to observe that it is 

 obtained from the milky juice of certain trees in South Ame- 

 rica, which juice is procured by incisions made in the bark of 

 the trees. When the watery part of the juice, which consti- 

 tutes more than half its weight, is evaporated, there remains a 

 solid elastic substance, which is the caoutchouc. The proper- 

 ties and peculiarities of this singular substance have been 

 mostly described in books of chemistry and other works, and 

 therefore need not here be enumerated. Some new charac- 

 teristics, however, seem lately to have been discovered by sub- 

 jecting the article to repeated distillation, and it is upon those 

 that we are about to make a few observations. 



Most if not all vegetable products are liable to be decom- 

 posed by heat. They are mostly resolved into solid, liquid, 

 and elastic substances, according, in some degree, to the 

 temperature. The instance of the destructive distillation of 

 * Conimunicatcil by the Aiillior. 



