Algist 1, 1920.] 



THE INDIA RUBBER WORLD 



A Direct Method for the Determination of Rubber Hydrocarbon in 

 Raw and Vulcanized Rubber/ 



By ir. K. Lc2cis and If. II. McAdams. 



INASMUCH as this paper will not deal with the structural for- .Votes: In order lo avoid loss of hromine vapor upon opening 



mula of rubber, the conventional formula (CoH.Jii will be the bottle after the bromination period, the bottle was cooled by 



used to designate rubber h,vdrocarbon, with the understanding immersion for a few minutes in ice water, in the dark, and the 



that this contains 3ii double, bonds. Two types of reaction are potassium iodide solution was introduced by means of 1-inch 



possible, involving in the first case, addition, and in the second, rubber tubing attached to the neck of the bottle and extending up 



substitution, of bromine. above the stopper. 



(C,oH„)»i.-f 2)iBr:= (C,„H„Br.)« (1) The carbon tetrachloride was puritied by subjecting it to the 



(C,„H„)H-t-HBr,= (C,„H,oBr)»t+»HBr (2) action of saturated chlorine water for several days in diffused 



In the second reaction it will be noted that two atoms of daylight, followed by washing with water and drying with calcium 



bromine are necessary to substitute one atom of hydrogen, there- oxide, previous to a distillation in which the fraction boiling 



by producing one formula weight of hydrogen bromide. vvithin one degree C. of the proper boiling point was taken. 



This paper deals with the application of the McIIhiney method, 



developed for unsaturated oils, to rubber hydro-carbon. Briefly, VULCANIZED RUBBER. 



it consists in determining by a volumetric method the substitu- The above results have shown the method to be satisfactory 



tier, which does occur under the particular conditions of the an- for raw rubber; it remained to adapt it to vulcanized rubber. 



alysis in question, and deducting twice the observed substitution Since carbon tetrachloride will not "dissolve" vulcanized rubber, 



from the bromine consumed, which gives the measure of the true a new "solvetit" had to be obtained, and the choice was tetra- 



bromine addition, from which the rubber hydrocarbon is readily chlorethane. 



calculated In addition to the rubber hydrocarbon, resins, and proteins 



RAW RUBBER PREPARATION OF PURE RUBBER HYDROCARBON P"""*^"' '"."^^' '"^^^'; vulcanized rubber may contain fillers and 



SOLUTION compoundmg materials, such as mnieral oxides or salts, carbon, 



mineral rubber, organic accelerators, vulcanized oils (factice). 



Plantation pale crepe was extracted overnight with acetone in ^^^^ ^^^^^^^^^ ^^^ ^^,pj,^^ combined as polyprene disulfide, 



the standard extraction apparatus to remove the resins, then care- rr H S "l 



fully dried, dissolved in pure carbon tetrachloride, and finally ^, " . , , ^ , 



£,. . ^ .. . • J iu • 1 ui it Tu The acetone extraction of the finely cut sample was made to 



filtered to remove the proteins and other insoluble matter. The , . , , , , , , , 



,,. , J , 1 J I, .■ 4. J » ■ remove not only resins but also free sulphur and other acetone 



resulting hvdrocarbon was analvzed by evaporation to determine , , , . , _, . . . , ,■ , , , ^ • 



^. , . , ,■ , 4 . , ■ , _ J ^i_- 1 Lu soluble materials. The rubber residue was dissolved by refiuxing 



the total solids present in a known volume, and this known rubber . , , , - r . , ,., , . ^ . 



.., . \ . J v-r • ■ u ..u \vith tetrach brethane" for several hours, diluted to a defimte 



hydrocarbon content was used as a basis of comparison with the . ,-,,,, 



,,1 „1 t=^ (•„. ,o f ^ k i,,„~;„ jj:»;„„ „, ^^^„,-u^a v, i„,„ volume with carbon tetrachloride, and allowed to settle, then an 



calculated ngures tound bv bromine addition as described below. . . . 



aliquot part was pipetted out for bromination as in Brandegee's 



PROCEDURE. method. The finely divided fillers were excluded from the aliquot 

 To a known volume of the above pure rubber hydrocarbon so- ^^'^ ^° '^"^^n "y P'^^'"^ a wad of cotton in the tip of the pipette, 

 lution, containing approximately 0.2 g. (C,.H,.)ji, a measured vol- ^''^ applying a gentle suction. 

 ume of bromine in pure carbon tetrachloride corresponding to ap- COMBINED SULPHUR PROCEDURE. 

 proximately 150 per cent excess bromine above that necessary -phg combined sulphur was found hy evaporating to dryness in 

 for addition was added, and the mixture was allowed to stand in g porcelain casserole an aliquot part of the tetrachlorethane solu- 

 glass-stoppered bottles for varying lengths of time in a dark ^jg^ f^gg from insoluble matter, and determining the sulphur by 

 closet at room temperature. After this exposure to bromination, j^e method of Davies.' This consisted in adding 10 cc. of sat- 

 10 cc. of a three per cent potassium iodide solution were added ^^^^^^ arsenic acid solution. 10 cc. of fuming nitric acid, and 

 to take up the excess bromine, and the resulting iodine was ,hrce cc. of bromine water and evaporating to a sirupy con- 

 titrated by means of 0.25 norma! standard sodium thiosulphate, sjstency. (If all the organic matter is not destroyed, more 

 using starch paste as an indicator. In order to determine the fusing nitric acid is added, 'and the mixture again evap- 

 substitution which had occurred, 10 cc. of five per cent potassium ^^^4^^ ^^ 3 sirupy consistency.) After the addition of a few 

 iodate were now added to convert the equivalent of the hydro- crystals of potassium chlorate, the solution is evaporated to dry- 

 gen bromide into iodine, which was then titrated to a second end- ^g^j^ heated to boiling with 50 cc. of ten per cent hydrochloric 

 point. A blank was run under the same conditions as the rubber ^gjj solution, filtered through paper, and diluted to 300 cc. with 

 determination in order to determine the bromine added to the distilled water in a beaker. The sulphuric acid is precipitated 

 rubber analysis, and to eliminate any error caused by impurities .^j barium sulphate by the addition of barium chloride, and dc- 

 in the reagents used. The sample calculation given below in- ,ermincd gravimetrically in the usual manner, 

 dicates the relations of the various ratings: 



Rubber taken = 0.2000 G. Thiosulphate Solution = 0.235 Normal CALCULATION OF TOTAL RUBBER HYDROCARBON. 



Equivalent Weight of Rubber Hydrocarbon, (CioHie)^ = 34 . ■ j • i_ 1 1 1 ^i r j 



Cc. Thio. The rubber nydrocarbon combined with the sulphur thus found 



For blank ■•■•••• .■•••. ^O-J^ is calculated by multiplying the percentage of sulphur by 



Excess found by first titration 38.00 " j 1 j o t- 



Consumed 32.00 r^ zj 1 -J^ 



Twice second titration. (2) (3.5) 7.00 L,„M,„ 1 JO 



True addition 25.00 _ or — 2.]3. 



25.00 X 34 X 0.235 X 100 , . , ,j. . q M 



= 100 oer cent theoretical addition -Jj "^ 



0.2000 X 1000 



eouri. April IMS. 1920. I'lfi. P^se 11. 



