648 



THE INDIA RUBBER WORLD 



[August 1, 1917. 



What the Rubber Chemists Are Doing. 



SYNTHETIC RUBBER. 



1\ a comprchcn.'^ivc article in "Metallurgical and Chemical 

 Engineering" (May 1, 1917), Andrew H. King illustrates the 

 possibilities should synthetic rubber be obtainable commercially, 

 by comparison with the case of synthetic indigo, which has 

 completely displaced indigo from natural sources. 



The present state of knowledge on the structure of the caout- 

 chouc molecule is given in historical review, following by for- 

 mulas, discussions of polymerization, methods of preparation of 

 butadiene, condensation, opening the benzene ring, fermentation 

 and dehydration. 



This is the concluding article of a series of three, the object 

 of which is to point out that if the seas are ever closed for tBe 

 importation of our rubber supply there are only three ways to 

 protect ourselves. 



1. Cultivate and harvest guayule by scientific methods. 



2. Develop something from milk weed or related plants. 



3. Work up a good synthetic rubber. 



METHODS FOR TESTS OF CHICLE. 



The folloxving methods by Dr. Frederic Dannerth are con- 

 densed from "The Journal of Industrial and Engineering Chem- 

 istry" (July, 1917). 



Chicle is valued on the basis of the following factors: (1) 

 Contained moisture; (2) shrinkage, when cleaned of dirt and 

 bark; (3) chewing quality of purified chicle; (4) color of the 

 crude chicle. 



Typical analysis of Yucatan chicle : 



Per Cent 



.Acetone-soU'ble matter (resins) 40.0 



Gutta and carbohydrates 17.4 



Proteins 0.6 



Sand and foreign matter 2.3 



Water 35.0 



Mineral matter (?sli) 4.7 



Crude chicle is sampled by cutting one poimd from the block. 

 This is rapidly cut into half-inch crumbs and stored for test 

 sealed in a "Lightning Jar." Wet chicle cannot be thus stored 

 more than one week, as molds grow rapidly, especially in the 

 dark. 



MOISTURE. 



A half grain of crude chicle is dried in an air bath about five 

 hours and not exceeding 50 degrees C. A glass dish two or 

 three inches in diameter with ground glass lid is used for the 

 sample. Fusion retards evaporation of the water. Drying is 

 complete when two consecutive weighings agree within one-half 

 per cent. 



Moisture in crude chicle may be determined simultaneously 

 with the resins. Boiling acetone removes resins and water from 

 the sample. The extract in the flask is dried at 105 degrees C. 

 and the residue in the thimble is dried in a similar manner. The 

 sum of these weights subtracted from the weight of the original 

 sample represents water. This method for determining moisture 

 is preferred in practice. 



VISCOSITY. 



Kerosene (boiling point above 140 degrees C.) is used zs the 

 solvent as the loss by evaporation is negligible. Commercial 

 chicle must be dried for 12 hours in a vacuum at not exceeding 

 70 degrees C. before solution. 



Twenty grams of dry chicle, weighed to tenths of a gram, 

 are placed in a wire basket fitted for a "Joint Rubber Commit- 

 tee" extraction apparatus. In the flask are placed 75 cc. of 

 kerosene. The basket is made of 100-mesh wire gauze and 

 retains any gritty and fibrous matter. The kerosene-chicle solu- 

 tion is diluted with kerosene to a concentration of 3) grams of 

 strained chicle in 100 cc. of liquid, .•\fter cooling to 20 degrees 



C. its viscosity is determined in a Stornier viscosimeter (The 

 Indi.v Rubber World, December 1, 1916) and the result ex- 

 pressed in revolutions per minute. 



KI-'.SINS. 



The chewing quality of chicle is due to the presence of resins 

 of suitable melting point. Mexican chicle has resin contents 

 averaging 60.8 per cent of the dry chicle. 



Acetone Soluble Matter. Five grams of crude chicle, granu- 

 lated to pass through one-eighth mesh screen, is extracted \\vc 

 hours in a Joint Rubber Committee extractor w'ith acetone of 

 boiling point not higher than 65 degrees C. The evaporated ex- 

 tract is dried to constant weight at a temperature not above 

 105 degrees C, cooled in a desiccator and weighed. The residue 

 is dried at 85 degrees C. If the acetone solution is allowed to 

 cool before distillation a large part of the resins separate out 

 as a wa.x-like incrustation. After all the acetone is expelled 

 and the temperature reaches 105 degrees C. the residual resins 

 appear quite clear and amber colored. 



MINERAL M.\TTER. 



One to two grams of dry chicle are incinerated in a crucible 

 inserted in an asbestos shield. The organic matter is volatil- 

 ized at low-temperature without ignition, after which the carbon 

 is burned off as usual. 



COLOKED SPOTS ON RAW RUBBER. 



B. J. Eaton, in the Agricultural Bulletin of the Federated 

 Malay States, discusses the development of chromogenic organ- 

 isms in dry rubber allowed to become damp. The colored spots 

 referred to are designated as "spot disease" and have been deter- 

 mined experimentally to be due to the growth of chromogenic 

 organisms induced by either rain or sea water wetting. Ten 

 days after wetting dry, clean pale crepe considerable develop- 

 ment of colored organisms occurred, resulting in patches of 

 orange, blue and yellow on the rubber. Dry, well-smoked sheet 

 rubber may develop mildew on the surface for similar reasons, 

 while low-grade rubbers may ferment and become tacky. 



The author notes several interesting observations in the course 

 of his investigations on the development of chromogenic organ- 

 isms in rubber. No development of pigment occurs in "slab" 

 rubber, which is slightly pressed coagulum, until the slab is cut 

 open, when pigment develops on the cut surface after a few 

 days. If sheet rubber is rolled into a cylinder straight from 

 the sheeting machine, no development of pigment takes place 

 until the sheet is cut open, when pigment develops on the cut 

 surface. When wet, thin crepe is rolled into a cylinder there is 

 invariably a great production of pigment due to the growth of 

 these organisms. From these experiments it seems that the 

 presence of air is necessary for the development of chromogenic 

 organisms, and this is excluded in rolled sheet or slab rubber. 

 Also it is probable that an excess of moisture may retard or pre- 

 vent the formation of the pigment, and that tlie pigment forms 

 later with the reduction of the moisture. 



VALUATION TESTS OF CRUDE RUBBER. 



Scientific and rule-of-thumb valuing of plantation rubber have 

 recently been compared by J. G. Fol for the Dutch Rubber Con- 

 gress. The report of the investigation is published in the report 

 of Department of Agriculture, Manufactures and Commerce, 

 under the title of "Mededeelingen van dem Rijksvoorlichtings- 

 dienst ten behoeve van den Rubberhandel en de Rubbernijverheid 

 te Delft." There were 137 specimens, 36 samples of sheet, all but 

 one of which were smoked, and 101 samples of crepe, six of 

 which were thick blanket. These were all judged in an empiric 

 way by the producers and their conclusions reserved and com- 



