392 



CAOUTCHOUC. 



Caout- Caoutchouc is variously acted upon by different 

 chouc. agents. When exposed to a high temperature, it is 

 softened, becomes viscid, swells, emits a peculiar odour, 

 and burns with a very bright flame. If a more mo- 

 derate heat be applied, it retains its viscidity, never 

 resuming its elastic state. 



The atmosphere affects the colour ; but we are 

 not aware of any alteration which it produces on the 

 other properties of caoutchouc. 



Water was supposed, by Grossart, to be a solvent 

 of this substance, merely because it is softened, 

 and becomes somewhat transparent on the edges, on 

 being immersed for some time in boiling water. It 

 is very clear, however, that this effect depends on 

 the increased temperature, rather than on the water 

 itself. When boiled for a very considerable time, no 

 alteration takes place, except in a way that is deci- 

 dedly referable to the agency of heat. By this heat- 

 ing, the caoutchouc is rendered so adhesive, as to ad- 

 rait of being united very closely by simple pressure. 



It was very soon determined, that alcohol does 

 not dissolve it. It, however, renders it colourless. 

 M. Macquer confirmed these observations. 



The same chemist also found, that sulphuric ether was 

 a solvent of caoutchouc ; but Berniard afterwards re- 

 peated the experiment without success. He also tried 

 the nitric ether, and found it to be a very imperfect sol- 

 vent. Mr Cavallo was the first that determined the 

 causes of this discordance, between two chemists 're- 

 markable for their accuracy. This philosopher 

 found, that ether is a solvent, only after having been 

 well washed with water. Subsequent experience has 

 shewn this statement to be correct. It is evident, 

 that Macquer and Berniard had used the same kind 

 of ether in two different states. On evaporating the 

 ether, the caoutchouc remains unaltered : hence, 

 from the solution, various instruments may be made 

 with facility. Pelletier found, that the solution is 

 considerably facilitated, by boiling the caoutchouc 

 for some time before it is put intp the ether. Dr 

 Roxburgh did not find that the nitric acid dissolved 

 the caoutchouc, which he obtained from the Urceola 

 elastica. 



The volatile oils dissolve caoutchouc ; but on eva- 

 poration, it remains clammy and unfit for any use. 

 The fixed oils have a partial effect when aided by heat ; 

 and melted wax dissolves a very minute portion. 



Dr Thomson discovered, that ammoniacal gas dis- 

 solves a very minute proportion of caoutchouc, al- 

 though Berniard had denied the action of the alka- 

 lies. The Doctor has further determined, that all 

 the alkalies produce similar effects. 



The acids decompose caoutchouc very partially. 

 Mr Hatchett obtained about 12 percent, of charcoal 

 from caoutchouc that had been charred by sulphu- 

 ric acid. When acted upon by nitric acid, azote, 

 carbonic acid gas, prussic acid gas, and oxalic 

 acid, are said to have been formed. 



Petroleum dissolves it, and it remains unaltered 

 after evaporation. 



When distilled, it gives out ammonia, a watery li- 

 quid, empyreumatic oil, and charcoal. 



Such are the leading properties that have been as- 

 certained of this singular substance. It exists in many 

 plants, in which it has usually been confounded with 

 other matters. In the fluid state in which it is found 

 in plants, it unites readily with water, by which means 

 it may be easily separated from the stalks. This fact 



is a valuable one, as it may hereafter be employed in 

 the manufacture of instruments made of caoutchouc. 

 When combined with resin, it may be separated by 

 alcohol ; and, for its separation from gum, or ex- 

 tractive, the following formula is given by Hermb* 

 stadt : " Digest a part of the plant containing it 

 (caoutchouc), first in water, and then in alcohol, 

 till all the substances soluble in these liquids are ex- 

 tracted. Dry the residuum, and digest it in four 

 times its weight of rectified petroleum. Express the 

 liquid part, by squeezing the substance in a linen 

 cloth. Let this liquid remain several days to settle, 

 then decant off the clear liquid part, mix it with a 

 third part of water, and distil ; the caoutchouc re- 

 mains behind. 



Opium is said to contain caoutchouc, and the inso- 

 luble part of mastic possesses some of its properties. 



Caoutchouc is used for various purposes. In South 

 America, whence it was first brought to Europe, it 

 is formed into solid masses, with which the natives 

 play at a game somewhat resembling that of fives. 

 It is used for bottles and boots, for which it answers 

 extremely well. It is also formed into torches, which 

 burn with great splendour. 



In Europe, it is commonly used to take out the 

 marks of blacklead pencils ; for syringes, bougies, 

 catheters, elastic tubes, and varnish. 



Many methods have been employed to fashion it 

 into the forms necessary for the above instruments. 

 The expense of ether, and the rapidity with which 

 it evaporates, precludes its use as a solvent ; and 

 the peculiar effect of the oils, already noticed, un- 

 fits the caoutchouc, after solution, for any purpose. 

 The best mode of forming tubes and bougies ap- 

 pears to be, to cut a bottle of caoutchouc into a thin 

 narrow slip, which must be heated in boiling water, 

 until the edges become transparent ; then to wind 

 the caoutchouc slip, accurately applying the edgea 

 to each other around a piece of cane, previously split 

 into two, and having a slip of whalebone interposed 

 between them. When the whole has been accurate- 

 ly applied to the surface of the cane, it may be plun- 

 ged into boiling water again, and any inequalities on 

 the surface removed. A slight varnish of the caout- 

 chouc applied to the whole surface, may render the 

 surface still smoother and more perfect. The slip of 

 whalebone being withdrawn, the cane may be readily 

 taken out, and the tube will be fit for use. Or 

 should the surface be unequal, it has been proposed 

 to immerse the tube or bougie into a glass tube filled 

 with the ethereal solution ; the diameter must scarcely 

 exceed that of the bougie : the whole apparatus is 

 then to be plunged into hot water, the ether will be 

 evaporated, and a smooth coating given to the in- 

 strument. This will be too expensive for common use. 

 Cloth impregnated with the recent juice of the 

 urceola is perfectly impervious to water, and may be 

 applied to a multitude of economical purposes. The 

 chief objection is the scarcity of the substance, which 

 enhances its value. It forms the best varnish for 

 balloons, and indeed for all those instruments that 

 ought to be impervious to water and air. See Thom- 

 son's Chemistry ; Murray's Chemistry ; Annales de 

 Chimie, vol. xi. xii. and xxiv. ; Philosophical Maga- 

 zine, vol. xxii. ; Aikin's Dictionary of Chemistry and 

 Mineralogy; Medical and Physical Journal, vol. iii. ; 

 Manchester's Memoirs, vol. ii. 2d series ; Asiatic 

 Researches } vol. v, (c. M.) 3 



Caout. 

 chouc. 



