September i, 1901.] 



THE INDIA RUBBER V/ORLD 



353 



SOLUBILITY OF CAOUTCHOUC AND GUTTA-PERCHA. 



By Dr. Theodor KolUr* 



DILUTED acids and concentrated alkalies do not attack 

 Caoutchouc, either at ordinary or at raised tempera- 

 tures. Concentrated sulphuric acid decomposes it, 

 likewise concentrated nitric acid. Six parts of fuming 

 nitric acid give, with one part of Caoutchouc, a solution, with 

 effervescence, which is precipitated in a flocculent state by 

 water. When Caoutchouc is digested for some time with spirit 

 of sal-ammoniac, it passes into an emulsion-like condition, and 

 gives a liquid with it, which leaves pure Caoutchouc upon 

 evaporation. Neither cold nor hot water dissolves Caout- 

 chouc, though boiling water extracts from several varieties 

 some resinous substance. In warm water it becomes very soft, 

 and swells considerably, making the whole mass more accessi- 

 ble to solvents, but prolonged exposure to the air restores it to 

 the former state. 



Payen found that a thin disc of Caoutchouc upon lying in 

 water for thirty days absorbed 18 to 26 per cent, of water, and 

 that in case of an absorption of 18 per cent, its volume increased 

 15.75 per cent, and its length 5 per cent. Absolute spirit of 

 wine penetrates Caoutchouc still more rapidly, especially when 

 it is repeatedly heated with it to ebullition. The weight of the 

 piece increased 18.6 per cent., the volume 9.4 per cent., the 

 length 4.6 per cent., the spirit even dissolving 2 per cent, of 

 the Caoutchouc besides. In ether, turpentine oil, and a mix- 

 ture of 100 parts of carbon-sulphide and 4 parts of absolute 

 spirit of wine, it swells up to 27 times its volume ; in a mixture 

 of 6 volumes of anhydrous ether and i volume of absolute 

 spirit of wine to 4 times its volume ; in rectified coal-tar oil up 

 to 30 times its volume. Ether, benzine, carbon-sulphide and 

 turpentine oil quickly permeate Caoutchouc and cause it to 

 swell up strongly, a portion being dissolved, but tenaciously 

 held back by the insoluble one, so that for extracting it large 

 quantities of the solvent are required. According to Payen, 

 Caoutchouc soaked in carbon-sulphide dissolves rather 

 quickly in spirit of wine. In 6 to 8 parts per 100 parts of car- 

 bon-sulphide it is again precipitated from this solution by 

 admixture of double the quantity of spirit of wine, but it 

 encloses much carbon-sulphide and spirit of wine, so that it 

 subsequently dissolves again. By repeated precipitation and 

 re-dissolulion it can be obtained in a transparent solution free 

 from dyestuflf, and the other substances occuring with it. 

 Parkes recommends as dissolvent the liquid, which is obtained 

 when sulphurous gas is conducted over camphor until the lat- 

 ter has deliquesced entirely. In fats, volatile and unctuous 

 oils it also swells up considerably, dissolving in many ; it dis- 

 solves very well and easily in Caoutchouc oil obtained by the 

 dry distillation of Caoutchouc. 



As a rule. Caoutchouc is dissolved by lavender oil as well as 

 by turpentine oil, but by linseed oil only when warm. Bouch- 

 ardat has made the observation that turpentine oil, by repeated 

 distillation at a higher temperature, alone or over bricks, under- 

 goes a change, which renders it far more suitable for the disso- 

 lution of Caoutchouc. With all dissolvents attention should 

 be paid to an absolute freedom from water; it is also advisable 

 to dry the Caoutchouc for some time, before the dissolving, 

 and very commendable are a previous boiling with soda solu- 

 tion or caustic soda lye and careful washing and drying. Most 

 solvents do not dissolve the Caoutchouc completely. If a com- 

 plete dissolution of the Caoutchouc is effected at a higher tem- 

 perature it suffers a decomposition, the solutions do not con- 



tain unchanged Caoutchouc and on evaporating leave behind 

 a mass of softer consistency and absolutely dillerent qualities, 

 so that it dries only with difficulty, even in thin layers. 



According to Hanausek, oil of turpentine and coal benzine 

 are especially good solvents for Caoutchouc ; 100 parts of oil 

 turpentine or coal benzine dissolve about 4 to 5 parts of Ceara 

 rubber, 5 parts of negroheads, 4.7 of Sierra Leone rubber. 



The most suitable solvents are ether (free from alcohol), 

 chloroform, carbon sulphide, coal benzine, and purified tur- 

 pentine oil. For industrial purposes solutions in ether are 

 useless. Turpentine oil only dissolves when very pure and 

 used hot. To prevent the viscousness of the solution, 2 parts 

 of turpentine oil has to be worked together with i part of 

 Caoutchouc into a thin paste and yi part of a hot, concentrated 

 solution of potassium-sulphide added. When the yellow liquid 

 has thickened, the Caoutchouc remains perfectly elastic and is 

 not viscous. If it is desired to unite pieces of Caoutchouc, the 

 best solvent is coal benzine, but the odor remains perceptible 

 for a long time. Chloroform being too expensive for ordinary 

 use, carbon sulphide is the best dissolvent. The solution dries 

 quickly owing to the volatility of the solvent. When alcohol 

 is mixed with the carbon sulphide, it does not exercise any 

 dissolving action, but only renders the Caoutchouc softer and 

 more fit for vulcanization. 



The preparation of a Caoutchouc solution is performed as 

 follows: Fill pure Caoutchouc, cut in small pieces, in a 

 spacious linen bag and suspend the latter by means of a thread, 

 in a bottle containing i liter of benzine, in such a manner as to 

 completely immerse it. After six or eight days the soluble 

 part of the Caoutchouc (40 to 60 per cent.) has been extracted 

 and the insoluble residue has swelled up to an enormous size. 

 The clear, slimy solution containing 1.2 to 1.5 per cent, of 

 dissolved Caoutchouc is subsequently kept in the dark. In the 

 light the Caoutchouc solution decomposes, becoming quite 

 thinly liquid ; even in the dark a change takes place, but much 

 more slowly. 



In order to bring the total of the Caoutchouc mass to a solu- 

 tion, HofTer causes Caoutchouc to swell up in carbon sulphide 

 (the swelling will take place quicker if the well closed flask is 

 allowed to stand in a moderately warm place) and adds, after 

 this end has been attained, 10 per cent, of absolute alcohol for 

 every 100 parts of carbon sulphide. After a few days a com- 

 plete solution will have formed in the flask, from which, after 

 prolonged rest, all foreign admixtures will settle to the bottom. 

 If the solution is mixed with a large quantity of alcohol, the 

 latter will precipitate the Caoutchouc again in a swelled state, 

 while the foreign bodies remain dissolved. By pouring off the 

 brownish solution from the precipitate, dissolving the latter 

 again and repeating the precipitation several times, the Caout- 

 chouc is obtained free from dyestuff as a perfectly white or 

 only faintly yellowish mass. 



It being desired to employ turpentine oil for the preparation 

 of Caoutchouc solutions, the same must be free from water (the 

 Caoutchouc itself may be kept anhydrous by drying it for a 

 week previous over sulphuric acid). 



The dehydration of the oil of turpentine is conducted in the sim- 

 plest manner by shaking the oil with about 10 per cent, of its 

 weight of English sulphuricacid in a well closed flask and leaving 



♦Translated for Thk India Rubber Wokld from a ^3,p^x\r\ Ntuste Er/tndungen 

 und ErfakrungtH^ Vienna, VII Jahrg. (ic^oo), pp. 293-296. 



