January 1. L91S.] 



THE INDIA RUBBER WORLD 



197 



Caoutchou, Mousse, or rubber loam, described lately in the 

 "Scientific American," is really sponge rubber very much sponged. 

 It is a French invention and is based on the fact of the increase 

 of the solubility 'if gases with the increase of pressure. 



To make it. rubber, softened by massing and partially vul- 



PHYSICAL TESTS OF RUBBER. 



Rubber Foam \- It Appears in* the Microscope. 



canized, is enclosed in a steel tube with nitrogen at a pressure 

 of 3,000 to 4,000 atmospheres. The gas dissolves the softened 

 rubber and, when the tube is opened, expands it to four or five 

 times its former volume, when it sohdifies. It is said to be of 

 use for a variety of purposes where any very light sponge 

 rubber could be used. -, 



7.. 



NEW PROCESS OF LATEX COAGULATION. 



According to the claiftii. of the patent taken out in Brazil by 

 Professor Heinrich Coloseus, of Berlin, it has been recognized of 

 late years that the quality of rubber is subject to wide variations, 

 in accordance with the mode of its extraction and coagulation. 

 Considerable progress has been realized in this matter, but with- 

 out a thoroughly satisfactory process having been discovered. 



In addition to the methods of smoking usual in Brazil, coagula- 

 tion has been effected by one or the other of two systems. By 

 the first, the rubber and the bodies which accompany it are 

 precipitated by the addition to the latex of various acids, while 

 by the second substances are added which precipitate or trans- 

 form into salts the solid bodies suspended in the rubber latex. 



The disadvantage of all these processes is that they precipitate 

 albuminous substances at the same time as the rubber, and in 

 such a form that they rapidly decompose, and lead to the decom- 

 position of the rubber. Under the new patent the albuminous 

 substances are eliminated in such a shape that their durable 

 stability is assured. 



For this purpose an alkali is first added to the latex, in partic- 

 ular hydrate of potassium or of sodium, or of any other sub- 

 stance with alkaline reaction, working with the formation of a 

 soluble salt on the albuminous and other bodies wdiich accom- 

 pany the rubber. If necessary the reaction can be completed by 

 heat. By the addition of heavy ferrous or alkaline-ferrous salts 

 hydrates or oxides, or of mixtures of these substances, the solu- 

 ble salts of the albuminous or similar substances are transformed 

 into compounds difficult or impossible to dissolve in water. 

 The separation of the solid bodies takes place either immediately, 

 after a protracted rest, or after heating. In the rubber as sep- 

 arated are then found the albumen or the albuminous substances, 

 or the saponifiable resins in the form of their insoluble salts. 



It is stated that the products obtained by the experiments made 

 on this system have been found of excellent quality. 



IX the "Bulletin de l'Office Colonial," Paris, Messrs. Heim 

 * and Cheneveau have lately dealt with the methods of physical 

 tests of rubber in connection with their commercial value, era- 

 phasizing the following points: 



I 1 he possibility of differentiating two rubbers by numbers 

 indicating their industrial value. In the present state of knowl- 

 edge, purely chemical determinations will pot solve the problem, 

 which calls for mechanical or physical tests. 



II. A rapid test of the crude material would simplify matters 

 a good deal. 



The phj include : Extensibility with constantly in- 



creasing loads ; elasticity of traction, cycle of hysteresis and 

 permanent elasticity; combined test of extensibility and elastic- 

 nerve"; successive cycles of hysteresis; extensibility with 

 constant charge; varying length of charge; tenacity; com- 

 pression with progressively increasing loads; elasticity of com- 

 pression ; extreme compression ; friction or abrasion and hard- 

 ness. 



III. Electric Tk- ■ Resistance of insulation; resistance; 

 dielectric constant; electrostatic rigidity. 



IV. Various Physical Tests: Action of heat; action of 

 light — coloration, absorption; solubility; viscosity of rubber so- 

 lutions ; adhesion ; absorption and diffusing of gases. 



V. Determinations have been tried of the viscosity of raw 

 material dissolved in appropriate solvents. These tests con- 

 sisted in dissolving the rubber in benzine and running off the 

 solution through a capillary tube. Tests of adhesion are often 

 effected by dissolving ,the rubber in oil of naphtha, but are of 

 no importance except jffojr rubbers used in making' 1 waterproof 

 fabrics. Other tests are those of the absorption of gas, only of 

 interest to the aeronautic industry, as well as heating the rubber 

 up to 100 degs. and noting the time it takes to become tacky. 



VI. For the establishment of a general and useful test it 

 has been found necessary to return to those long used for vul- 

 canized rubh' r.. Plantation Para, it is added, tears easily, its 

 homogerieousness being only apparent. A test of this character 

 only appears possible with a homogeneous layer of rubber of 

 regular thickness. 



VII. In tests of vulcanized rubber, mixed with sulphur, hot 

 vulcanization seems to give better results than the cold process. 

 The proportion of sulphur must not be too small nor too large. 



VIII. For a long time traction tests have been made with the 

 traction machine or dynamometer for defining tenacity and ex- 

 tensibility. Test pieces have generally the shape of prismatic 

 bars, fixed at their extremities to the jaws of the machine. Two 

 lines traced on the margin of the bar serve to indicate the ex- 

 tension to the breaking point. For this work it is found that 

 moulded test pieces are preferable to cut ones. 



Laws of more or less complicated nature, determined by the 

 successive extensions and contractions of test pieces, afford a 

 certain test of rubber, defining its "cyclic fatigue" ; the rubber 

 assuming a more stable condition, wdiich, however, is not easily 

 clei'ned. 



It may be concluded that the test of extensibility alone is in- 

 sufficient, the addition of the test of elasticity being required 

 to bring out the other fundamental qualities of the rubber. The 

 larger the number of different qualities to be defined the more 

 exactness will there be in the determination of the various 

 grades of rubber. 



A point to be noted is that when rubber has been stretched 

 under a continuous load, applied gradually or once for all, the 

 test piece increases in length. 



TX. The most precise and rational course is that of comparing 

 under identical conditions the technical properties of the rubber 

 to be tested with those of a standard sample, both having been 

 vulcanized without any other weighting substance than sulphur. 



