356 



THE INDIA RUBBER WORLD 



[March 1, 1920. 



Countries. W 

 British- 

 Mauritius 



Uifion*of 'Soilth ' Africa ".'.'.'.'.'.'. '. '. '. '. '. 

 (Duty based on the current value for 

 of purchase, including value of packii 

 exceeds 5 per cent.) 



Zanzibar ,• • • ■ • • ■ 



(The dutiable value of imports from Europe 

 be the cost price [with charges). ' 

 invoice price [exclusive of charges], 



America 



. 5 per ( 



ased by 15 per 



(In .MexandVia a wharfage tax of one-half 

 other ports different rates are imposed.) 



French Algeria 



(Imports from France an 

 other countries are subje 

 of France.) 



COV'NTRIE! 



Italian — 



Somaliland 

 Morocco . . . . 



Rate 



Per Cent- 



.\d Valoren 



(Duty based on 

 per cent. O: 



valorem rate.! 

 New Zealand . . . . 



(Impor'ts'of fo'rVii! 



Philippine Islands . 



(Imports of foreig 



fair market value F. O. B. at port of export, phis 10 

 casings weighing over 2J/2 pounds and inner tubes 

 each, 48.6 cents per pound, if higher than the ad 



xed 25 per cent 



Free 

 Free 



A Rapid Method for the Determination of Sulphur in Rubber 



Mixtures." 



By G. D. Kratz, A. H. Flower and Cole Cootidge. 



THIS INVESTIGATION Was primarily undertaken in order to find 

 an accurate and rapid inethod for the determination of sul- 

 phur in rubber mixtures, appHcable to both vulcanized 

 and unvulcanized samples containing various amounts of sulphur. 

 Further, it was desired that the results obtained should be com- 

 parable with those obtained by the well known Carius method, or 

 the fusion method of Waters and Tuttle", as adopted by the 

 United States Bureau of Standards. Both of the preceding meth- 

 ods, while accurate, involve a somewhat tedious procedure. 



CLASSIFICATION OF METHODS. 



It will not be necessary to review all of the methods which 

 have been proposed for the determination of sulphur in rubber. 

 Without considering their priority, it will suffice to recall that 

 they can be grouped roughly under three general classifications — 

 direct fusion, solution with electrolytic oxidation and solution, or 

 wet oxidation, with or without subsequent fusion. 



Of the direct fusion methods, the use of Eschka's mixture, as 

 proposed by Esch', and the zinc oxide-potassium nitrate fusion 

 mixture, proposed by Kaye and Sharp', are the best known. The 

 former, although quite accurate, is not sufficiently rapid for gen- 

 eral analytical work, while the spurting occasioned by the fusion 

 of rubber with zinc oxide and potassium nitrate is a serious ob- 

 jection to the latter. 



The electrolytic oxidation method of Gasparini" has been 

 adapted especially for rubber by Hinrichsen* and by Spence and 

 Young'. The latter modification, in particular, gives very satis- 

 factory results, but requires the use of special apparatus, the in- 

 stallation of which is not warranted in all laboratories. 



The method of Henriques', however, which involves wet oxida- 

 tion and subsequent fusion, probably has received the most at- 

 tention and has been made the subject of the greatest number of 

 modifications, among which is that of Waters and Tuttle. The 

 subsequent fusion of the product of the oxidation with nitric acid 



1 Published by courtesy of the American Chemical Society. Paper read 

 before the Rubber Division of the American Chemical Society, at Phila- 

 delphia, Pennsylvania, September 2-6, 1919. 



= ".Tournal of Industrial and Engineering Chemistry," Vol. 3. 191 1, page 734. 



= "Chemiker Zeitung," Volume 28, 1904, page 200. 



"■The IndiaRubbcr Jourral," Volume 44, 1913, page 1189. 



» "Gazetta Chimica Italiana," Volume 37, No. II. 1907, page 426. 



""Kolloid Zeitsc'.irift," Volume 8. 1911, page 248. 



'"Journal of Industrial and Engineering Chemistry," Vol. 4, 1912, p. 413. 



' "Zeitschrift Angewandter Chemie," Volume 34, 1899, page 802. 



with sodium carbonate-potassium nitrate mixture, however, limits 

 the rapidity with which this determination can be made. Several 

 methods have been devised to avoid the use of a fusion mixture. 

 The best of these have been proposed by Roth", Stevens'", and 

 by Rosenstein-Davies". Stevens' method, which has appeared 

 since the results reported in this paper were obtained, has not 

 been compared with our own. It would appear, however, that in 

 it Stevens has modified Roth's method in such a manner that the 

 objections to the latter method, noted by the Netherlands Gov- 

 ernment Institute, have been largely eliminated. The Rosen- 

 stein-Davies method is based, primarily, upon the solution and 

 wet oxidation of the rubber by a nitric acid-bromine water mix- 

 ture. In order that this oxidation be complete, and the necessity 

 of subsequent fusion be eliminated, it is required that the oxi- 

 dation be effected at a higher temperature than it is possible to 

 obtain by heating with nitric acid and bromine water alone. To 

 elevate the boiling point, a quantity of arsenic acid is added. 



Our experience with the above method has led us to depreciate 

 the use of arsenic acid for the purpose intended. When em- 

 ployed in the recommended quantity (12.5 gms.), it is difficult to 

 remove it entirely from the barium sulphate precipitate. Conse- 

 quently, in our method, in order to elevate the boiling point, with 

 a substance which can be easily washed free from the final pre- 

 cipitate, we have substituted zinc oxide for arsenic acid. This 

 substitution, while it effects even a higher elevation in the boiling 

 point than is obtained with arsenic acid, has the further advan- 

 tage of permitting the subsequent fusion being carried to dry- 

 ness ; in the case of the Rosenstein-Davies method, evaporation is 

 continued to syrupy consistency only. Thus, the carrying to dry- 

 ness, or, as wc have termed it, "baking" of the residue, insures a 

 more complete oxidation than is obtained by the above 

 method, and the final oxidation takes place at a temperature 

 far in excess of the boiling point of arsenic acid, .\fter "baking," 

 the residue is taken up in hydrochloric acid, and the zinc is elim- 

 inated — as the readily soluble chloride which is easily washed 

 from.the barium sulphate precipitate. 



In applying our method, we have found the following procedure 

 to give excellent results : 



' "Communications of the Netherland Govcrnme: 

 the Rubber Trade and the Rubber Industry," Volu 

 ""Analyst," Volume 43, 1918, page 377. 

 ""Chemist Analyst," Volume 15. 1915, page 4. 



