January 1, 1919.] 



THE INDIA RUBBER WORLD 



197 



the: 



elongation, 



takes place requiring more strain to prodii 

 because the rubber gains in stiffness. 



2. After adding the extracted resin the original diagram of 

 elongation is recovered except that the curve does not extend 

 quite as far. 



3. Addition of double the quantity of resin produces a greater 

 elongation for the same stress, the rubber thus having become 

 more "supple." 



It should not be lost sight of that the contradiction between 

 the above-mentioned positive correlation and the influence of 

 resins may be apparent, no corresponding vulcanization co- 

 efficients having been determined. It is possible that the resins 

 have an accelerating influence on the binding of sulphur, or they 

 may cause a marked decline of the mechanical properties. 



It should further be noted that by "percentage of resin" is de- 

 noted the acetone extract, and that these terms are not identical, 

 as the acetone extract also contains non-resinous or nitrogenous 

 compounds. Possibly some of the ingredients of this acetone 

 extract have an accelerating effect and it may be because of this 

 that the correlation between velocity of vulcanization and percent- 

 age of resin is not more distinct. 



From the data for 214 samples of first latex crepe Van Rossem 

 found that there exists in general no correlation between the per- 

 centage of ash in the raw rubber and the velocity of vulcanization. 



From 134 samples he determined that there exists no correlation 

 between the nitrogen percentage of the raw rubber and the vul- 

 canization coefficient. 



In this respect Clayton Beadle and Stevens have shown that 

 the insoluble part, rich in nitrogen, accelerates vulcanization, and 

 Stevens found that different nitrogenous compounds, such as 

 peptone and casein, act in the same way. These tests retain their 

 value, but, according to the preceding, the more or less accelerat- 

 ing action of the so-called insoluble part may no longer be at- 

 tributed to the nitrogen percentage. This does not mean that 

 artificially added nitrogenous compounds may not act on the 

 velocity of vulcanization, nor should it prevent other natural in- 

 gredients in the raw rubber from acting in a similar way. 



No correlation exists between the degree of acidity of the rub- 

 ber and the velocity of vulcanization. This is somewhat surpris- 

 ing, since acid acts to retard the velocity. In the meantime it 

 should be remembered that the degree of acidity can be only 

 incompletely determined. 

 Fillers and .Accelerators and the Vulcanization CoEFFiaENT. 



The addition of not too large quantities of inorganic fillers 

 which are inactive in respect to sulphur, does not practically 

 change the velocity of vulcanization. 



Whether an inorganic or an organic material will act as an 

 inert filler or as a catalyst in the vulcanization process is uncer- 

 tain of prediction. The action of old ground rubber, reclaimed 

 rubber and rubber substitutes is a study of great importance, but 

 this for the present is prevented by a number of difiiculties. 

 {To he continued.) 



METHODS OF ANALYSIS. 



DETERMINATION OF FREE CARBON IN RUBBER GOODS. 



AH. SMITH and S. W. Epstein, of the Bureau of Stand- 

 • ards, read before the Rubber Section of the American 

 Chemical Society at Cleveland, September 10 to 13, 1918, a paper 

 on the determination of free carbon in rubber goods. Follow- 

 ing is an abstract of their investigations and conclusions and 

 their method of analysis in full : 



The authors state that the main object in the determination 

 of free carbon in rubber goods is to permit the determina- 

 tion of the rubber content by difference. The most widely used 

 method for the determination of rubber is to calculate it as the 

 difference between 100 per cent and the sum of ash, total sul- 

 phur, and various extracts. This method is subject to wide 



error when free carbon is present and no allowance is made 

 for it. 



The nitric acid methods of Henry William Jones' and of 

 W. A. Caspari^ were not found entirely satisfactory. The 

 authors have found that the action of nitric acid is to attack the 

 carbon of lampblack and gas black and it is necessary to correct 

 the analytic results as obtained by ignition loss to compensate 

 for the error caused by the formation of compounds from the 

 free carbon. The attack of amorphous carbon by nitric acid 

 renders an accurate determination by this method impossible, 

 but the error is sufficiently uniform and small to allow practical 

 determinations. 



DETAILS OF METHOD AS FINALLY ADOPTED. 



Extract a one-gram sample for six hours with acetone and 

 then for three hours with chloroform or carbon bisulphide. 

 Transfer the sample to a 250 cc. beaker and heat on the steam 

 bath until it no longer smells of chloroform. Add a few cc. of 

 hot concentrated nitric acid and allow to stand in the cold for 

 about 10 minutes. Add SO cc. more of hot concentrated nitric 

 acid, taking care to wash down the sides of the beaker. Heat 

 on the steam bath for about one hour or until the disappearance 

 of all bubbles or foam from the surface. Pour the liquid, while 

 hot, into a Gooch crucible containing a fairly thick pad of ig- 

 nited asbestos. Filter by applying gentle suction and wash well 

 with hot concentrated nitric acid. Empty the filter flask, wash 

 the filter alternately with acetone and benzol until the filtrate is 

 colorless. Next wash it well with a hot 15 per cent solution 

 of sodium hydroxide. Test for the presence of lead by running 

 some warm ammonium acetate solution, containing an excess 

 of ammonium hydroxide, through the pad into a solution of 

 sodium chromate. If a yellow precipitate forms, the pad must 

 be washed with the ammonium acetate solution until the wash- 

 ings no longer precipitate the sodium chromate solution. Next 

 wash the residue well with warm five per cent hydrochloric acid 

 solution. Remove the crucible from the funnel, taking care 

 that the outside is clean, and dry it in an air bath for lyi hours 

 at 150 degrees C. Weigh, burn off the carbon at a dull red heat, 

 and reweigh. The difference in weight represents approximately 

 105 per cent of the carbon originally present in the form of lamp- 

 black or gas black. 



It is recommended that O.S-gram samples be taken for com- 

 pounds containing over ten per cent of free carbon and one- 

 gram samples be taken for compounds containing less than this 

 amount. 



authors' remarks on method. 



The factor of IDS per cent as a ratio between the ignition loss 

 and the amount of carbon present was arrived at from the re- 

 sults of a large number of determinations made at the Bureau 

 of Standards. Gas black determinations ran from 101 to 106 

 per cent and lampblack determinations from 100 to 108 per cent. 

 Results were obtained on different samples containing large 

 amounts of mineral rubber, lead (both in the form of oxide 

 and sulphate), reclaimed rubber of various kinds, glue, substi- 

 tute, sulphides of antimony, talc, etc. In all cases the results 

 came between 101 and 108 per cent of the carbon originally 

 present. By using the factor of 105 per cent, the maximum di- 

 vergence is four per cent and the usual divergence very small. 



In our analysis of the gas black and lampblack used in our 

 experiments, we determined the volatile loss at 100 degrees C, 

 the acetone extractable matter, and the ash, and assumed the 

 remainder of our samples to be carbon. Our results have been 

 calculated to this basis, and justify the method for routine 

 laboratory use. 



Replete with information for rubber manufacturers — Mr. 

 Pearson's "Crude Rubber and Compounding Ingredients." 



