December 1. 1914.] 



THE INDIA RUBBER WORLD 



127 



Fir.. No. 4. 



Press and Sample 

 Cutter. 



THE III Kl U HI i I'llil S 



ITS Ml I HI IDS OF 



TESTING. 



Dppartment of Commerce. 



Bureau of Standards, 



\\ ashington. 



The methods given be- 

 li iw are thi isi now in use 

 at the Bureau of Stand 

 ards and are offered es- 

 sentially as they appear in 

 the sheets of instructions 

 handed to all i ubbi I 

 analysts in the Bureau. 

 They arc not entirely 

 original, but have been 

 compiled from the various 

 publications on rubber 

 analysis and from the in- 

 formation gained through 

 the routine testing of rub- 

 ber goods for delivery on 

 government contracts, and 

 co-i iperative research with 

 various scientific organiza- 

 tii ms. I hese methods are 

 always subject to revision 

 whenever the I'urcau is 



convinced that changes would improve them. 



PREPARATION OF SAMPLES. 



1. Soft Rubber — Prepare a sample of not less than 25 grams, 

 taking pieces from various parts of the original sample. With 

 those having cover and tube, separate samples of each shall be 

 made. From lire hose remove the backing before grinding. 



2. Grinding. — The sample shall be cut into small pieces and 

 then run through grinder, taking for analysis only such material 

 as will pass a 20-mesh sieve. Care must be taken to see that 

 the grinder does not become appreciably warm during the grind- 

 ing. If the nature of the material is such that it gums together 

 so that it will not pass through the sieve (as would be the case 

 with undervulcanized samples), it will be sufficient to pass the 

 material through the grinder twice and accept all the material 

 for the final sample. Crude rubber shall be cut with scissors. 



3. Hard Rubber. — Samples of this material shall be prepared 

 for analysis by rasping. 



REAGENTS. 



4. Acetone shall be freshly distilled over anhydrous potas- 

 sium carbonate, using the fraction obtained at 56 to 57° C. 



5. Alcoholic potash shall be of normal strength, made by 

 dissolving the required amount of potassium hydroxide in abso- 

 lute alcohol, and allowing it to settle. Only the clear solution 

 shall be used. 



6. The nitric acid-bromine reagent shall be prepared h\ 



ble excess ..I bromine to concentrated nitric acid, 

 shaking thoroughly, and allowing it to stand for some hours 

 bi lore using. 



7. The fusion mixture for sulphur determinations shall be 

 made by mixing equal quantities of sodium carbonate and pow- 

 dered potassium nitrate. 



8. All reagents shall be oi C. P. quality. 



9. Barium chloride solution shall be made by dissolving 100 

 grams of barium chloride in one liter of distilled water, and 

 adding two or three drops oi com hydrochloric acid. If there 

 is any insoluble matter or cloudiness, the solution shall be 

 healed on the steam bath overnight, and filtered through 589 

 blue-ribbon filter paper. 



ANALYSIS. 



I — Mechanical Goods. 



10. Acetone Extract. -Place a 2-gram sample in an acetone 

 extracted S. & S. paper thimble, and extract continuously with 

 acetone for eight hours, unless the solution in the thimble is 

 still colored" at the end of that tune, when the extraction shall 

 proceed the next day for a further period of four hours. Trans- 

 Eei the extra, t to a tared LOO or 150-cc. Erlenmeyer flask, u 

 chloroform or benzene for dissolving any material which may 

 have separated from the solvent during the course of the ex- 

 traction. Drive off the solvents at as low a temperature as pos- 

 sible, using a gentle current of air. Dry the flask and contents 

 in an air bath, at 90 to 95° C. ; cool and weigh. Call the residue 

 "acetone extract, uncorrected." Calculate the results to per- 

 centage. 



11. Free Sulphur.— Add to the lla I. n..m par. 10, containing 

 the acetone extent, uncorrected. 50 to 60 CC. of distilled water, 

 and 2 or 3 CC. of bromine. (If the acetone extract indicated a 

 large amount i t free sulphur, the amount of bromine used may 

 lie increased). Heat gentlj on the steam bath until the solu- 

 tion is practically colorless, filter into a 250-cc. beaker. Cover 

 the beaker with a watch glass, heat to boiling on the steam bath, 

 add 10 cc of 10 per cent, barium chloride solution, and allow 

 the precipitate to stand overnight. The next day filter the pre- 

 cipitate through an 11-cni. 590 S. & S. filter paper. Ignite in a 

 small porcelain crucible, using a small Bunsen flame, and not 

 allowing the paper to inflame; cool and weigh. Calculate the 

 barium sulphate to sulphur by means of the factor 0.1372, and 

 calculate the percentage of free sulphur. 



12. Ash. — Wrap a 1-gram sample in an 11-cm. 590 S. & S. 

 filter paper, and after extracting with acetone for four hours, 

 transfer to a medium sized porcelain crucible and ignite at the 

 lowest possible temperature; cool and weigh. 



13. Sulphur in Ash. — Add a few drops of cone, nitric acid 

 to the ash from par 12, stir with a small glass rod. and evapo- 

 rate off the excess acid on the steam bath. Add 5 grams of 

 fusion mixture (par. 7), and heat until fused. When cool, place 

 the crucible in a 400-cc. beaker, cover with water, and heat on 

 the steam bath for two or three hours. Filter into a 600-cc. 

 beaker (reserve the insoluble residue for testing according to 

 par. 14), add 7 to 8 cc. cone, hydrochloric acid to the filtrate, 

 cover, and heat to boiling on steam bath. Add 10 cc. of 10 per 

 cent, barium chloride solution, and allow to stand overnight. 

 Treat the barium sulphate precipitate as under par. 11. Cal- 

 culate to sulphur by the factor 0.1372 



Fig. No. 5. Set of Rubber Mills Geared to, and Operated by. a Motor. 



