18 



THE INDIA RUBBER WORLD 



[October 1, 1920. 



antimony trichloride was siphoned from the bottom. To this 

 we added sufficient water to prevent crystallization. Tlie sub- 

 stance is antimony trichloride with one molecule of water. 

 This is a deliniie chemical compound, fairly stable; and does not 

 change to antimony tri-o.xide. This material, when added to 

 an excess of water, is precipitated as antimony oxychlorlde, 

 which is the most satisfactory substance to convert to oxysul- 

 phide with sodium thiosulpliate. If precipitation is carrica out 

 properly crimson antimony will result, which will cure satis- 

 factorily. 



COMMEBCIAL PROCESS 



The following procedure will give good results on a com- 

 mercial scale : 



To 135 pounds of antimony trichloride add 15 pounds of 

 water to keep it in a liquid and stable form while it is being 

 manufactured. This is poured into a large tank containing 

 about 60 cubic feet of water, where it is slightly mixed by 

 wooden paddles and converted to antimony oxychloride. At 

 this point add 21 pounds of wliiting to reduce the acid con- 



centration so that the formation of antimony oxysulphide is 

 not hindered when the thiosulphate is added. This step in 

 the procedure is important; for if the reaction is attempted at 

 too high an ,icid concentration, side reactions take place. Four 

 hundred eighty pounds of commercial sodium thiosulphate are 

 now poured into the lank, and the whole immediately agitated 

 by four steam jets. The steam, serves the double purpose of 

 agitating and heating the solution. The heating is continued 

 for approximately ten minutes, or until the desired color is 

 obtained. The steam is then shut off and approximately 250 

 cubic feet of water quickly run into the tank to stop the reaction. 

 (The time of heating depends on local conditions.) 



The material is now allowed to settle and is washed tliree 

 times by decaniation. It is then washed free of sulphurous 

 acid in a filter press, and dried at a low temperature. 



We have been continuously manufacturing crimson antimony 

 by this method since the spring of 1915, and during that time 

 have had only 250 pounds of unsatisfactory material, and this 

 was due tu carelessness. 



Some Aspects of the Stress-Strain Curve 



By IVilliam B. IViegaiid' 



MUCH of practical value will be found in the following 

 excerpts from Mr. Wiegand's interesting paper, read he- 

 fore the Rubber Section of the Toronto Branch of the 

 Society of Chemical Industry, February 27, 1920. 



STRESS-STRAIN RELATIONSHIP OF RUBBER 



Among the many interesting physical properties of rubber, 

 perhaps the most extraordinary is its stress-strain relationship. 

 The general characteristics of the rubber stress-strain curve are 

 familiar to everyone. They were first described in detail by 

 Yillari in 1869. Hooke's Law of proportionality of stress to 

 strain, which is universally true of most of the structural mate- 

 rials within their elastic limits is, of course, not valid. The ratio 

 of stress to strain is constantly changing. In other words. 

 Young's modulus of elasticity is in the case of rubber not a con- 

 stant but a rate. Nevertheless, rubber is the only substance for 

 which Young's modulus is an>-thing else than a mathematical 

 calculation. You can actually measure Young's modulus in the 

 case of rubber, because you can stretch it to twice its length and 

 measure the stress required to do so. 



Rubber is the only substance for which the elastic limit ex- 

 tends out as far as the actual rupture point. Whereas, in the 

 case of metals, the first part of the curve is stiff and the latter 

 parts show a yielding region, vulcanized rubber is yielding at 

 first but stiffens or tightens up later on. These extraordinary 

 stress-strain relationships of rubber attracted the attention of 

 some of the most brilliant physicists of the 19th century. 



The most exhaustive and masterly studies of the elastic prop- 

 erties of vulcanized rubber were carried out by Professor H. 

 Bouasse of the University of Toulouse, who published his 

 memoirs in 1904. Bouasse had carried out extensive work on the 

 elastic properties of other materials and was attracted to rubber 

 by the unequalled large scale of its properties of extension. He 

 saw an opportunity of, as it were, magnifying the ordinary 

 elastic constants and being able to study the phenomena of hys- 

 teresis and of the effect of temperature on these properties to 

 better advantage. Bouasse worked in the main with pure gum 

 mixings containing only rubber and sulphur. 



The following are examples of Bouasse's well-established gen- 

 eralizations. They are valid both for pure gum and for heavily 

 compounded mixings. 



•Director of Manufarturing. .^mcs-^olclcn•McCready, Limited, Toronto, 

 Ontario, Canada. 



1. The elastic modulus decreases with increasing elon- 

 gation, passes through a minimum and then increases 

 rapidly up to the breaking point. 



2. As the cycles are repeated the modulus correspond- 

 ing to any given elongation decreases, first, very 

 quickly, then slowly, finally reaching a practically 

 constant value. Thus, in arbitrary units, a series of 

 values for the first three cycles (at a given elonga- 

 tion) were 816, 535, and 460. 



3. The hysteresis in the moduli is also very great after 

 the first cycle, but is already small in the third cycle, 

 and after five cycles is almost gone. 



Perhaps Bouasse's broadest generalization, and one which has 

 profound technical significance, is the following: 



Every stretching of vulcanized rubber, every re- 

 duction in length, in general every change of form, 

 tends to diminish the value of the modulus corre- 

 sponding to any given elongation. Also every rest 

 tends to augment it and this augmentation increases 

 in proportion as the position of rest is nearer to zero 

 extension. 



Practical illustrations of this will occur to all. A stiff rubber 

 band can be "softened" by a few preliminary stretchings. A 

 laboratory test piece which slips out of the jaws of the testing 

 machine before rupture gives, on retesting, quite abnormal 

 values. In short, the physical properties of vulcanized rubber 

 (as of course those of crude rubber) are a function of its pre- 

 vious life history. 



HYSTERESIS 



Let us turn to the question of the retraction curve, which dif- 

 fers markedly from the extension curve. The area contained 

 between the two curves is called the hysteresis loop. There 

 is no more important quantity in the whole rubber technology 

 than the area of this hysteresis loop. Boileau, in 1856; Villari, 

 in 1869, and, above all, Bouasse and Carriere, in 1903, have, along 

 with others, been pioneers in the study of hysteresis. These 

 workers found that the hysteresis diminished as the number of 

 cycles increased, and finally reached an approximately fixed value. 

 The difference between the first two cycles was greater than 

 that between any other two. Schwartz found, in 1910, that the 

 area of the loop became fixed sooner in a high grade than in a 

 low grade of rubber. He also found that when cycles were gen- 

 erated to a constant final load, the increasing extension at the 



