THE INDIA RUBBER WORLD 



What the Rubber Chemists Are Doing. 



THE DETERMINATION OF SUBSTITUTE IN RUBBER.' evident from the ligures obtained from Nos. 7 lo 13 having been 



THE ACCURATE iiETERMiNATioN of substitute in rubber articles treated for three hours (figures between parentheses), 

 is somewhat difficult. The method usually followed for The last column proves the important fact that in many cases 

 an appro.ximale test is as follows: the determination of substitute yields figures which, according to 

 Part of the residue of the acetone extraction is heated for the method followed up to the present, arc considerably too low. 

 four hours in a flask with reflux condenser with 50 cc. of half- Xo better results were obtained with stronger alcohohc potash 

 normal alcoholic potash solution. It is then filtered and the solution. Normal solution, instead of half-normal, caused a sam- 

 residue washed a few times with boiling alcohol and then with pie witli 10 per cent substitute to yield only 0.8 per cent alcoholic 

 boiling water. Filtrate and washing liquid are evaporated to 15 potash solution extract. A small improvement was noted on very 

 cc, brought into a separating funnel, and after acidifying with finely cutting the samples, but even then the results were low. 

 hydrochloric acid, shaken with ether. The layer of ether is The low results were due to inability of the alcoholic potash 

 brought into a weighed flask, the ether is evaporated, the flask solution to penetrate completely the acetone extracted sample, 

 is dried at 100 degrees, and the increase of weight of the flask It was demonstrated experimentally that extraction with half- 

 indicates the percentage of factis acids. normal alcoholic potash after suitable swelling of the sample. 

 The determination takes place in the material previously ex- whether vulcanized or unvulcanized, in benzene gives satisfactory 

 traded with acetone for reason that rubber resins are also partly results provided the following precautions are observed. 

 saponifiable.= However, the substitute also dissolves partly in ]. Filtrate and washing liquid must be evaporated as far as 

 acetone, and this part varies for the different kinds of substitutes. possible. The reason for this has to be looked for in the 

 The percentage found in the alcoholic potash extract is therefore fact that otherwise benzene is not sufficiently expelled andl 

 too low for two reasons : _ ,1,^, therefore extraction with ether by shaking is not com- 



1. One part of the substitute is extracted with the acetone; plete (compare results under A and B). 



2. With the determination of the percentage of "factis acids" 2. Benzene must be present in excess, giving toolowr results- 

 the real substitute is not actually expressed. when this is not the case (compare under D) ; 1 to 6 con- 



The second error is not to be avoided but can never be con- ^^'" '"'""^' ^""^ and could suffice with 15 cc. benzene; 7 to 



siderable. To correct the first one as much as possible it has '^' '''^''^ '^° "°' <=°"'^'" ^'"y '^'"'^^^' '^""^'> ^^-J"'^^ ^' 



been proposed to determine the other substances in the acetone ^'""'^ ^0 cc. benzene (compare results under B and C). 



extract, and to conclude therefrom what percentage of substitute ^- ^he time of swelhng also has some mfluence. It appeared 



is present in the acetone extract. The percentage of factis acids '° ''^ desirable to let the rubber stand over one night with 



found as alcoholic potash extract increased by the percentage of benzene (compare results under E). 



substitute in the acetone extract, yields then the total substitute. details of improved method. 



.•\lthough this method is in general use,' a doubt arose when T«^' grams of acetone-extracted rubber is covered with 20 cc. 



repeatedly using it as to the accuracy of its results. For that rea- benzene and left for one night; 40 cc. alcoholic potash solution, 



son an investigation was decided upon and tests were carried out 0-5 N, is added and the liquid is boiled for about four 



on a number of rubber mixings with substitute of which the 'loui's with a reflux condenser on a water bath. It is then filtered 



composition was entirely known. a"d the residue washed with boiling alcohol and then with boil- 



The rubber used was Hevca cr£pe with an acetone extract of '"S \\ater. Filtrate and washing liquids are evaporated nearly 



three per cent. As vulcanizing does not appreciably change the 'o dryness (3 to 5 cc), rinsed into a separating funnel, and after 



acetone extract, the percentage of substitute could be calculated in acidifying with hydrochloric acid, extracted with ether by repeated 



the acetone extract of the vulcanized samples, the percentage of shaking. The layer of ether is brought into a weighed flask, the 



free sulphur being known. ether is evaporated and the flask dried at 100 degrees Centigrade. 



DETERMINATION OF SUBSTITUTE IN VULCANIZED RUBBER. The author's investigation further demonstrated that the de- 



After previous extraction with acetone the alcoholic potash termmat.on of substitute m compounds of rubber which contain 



extract was determined in two grams of the acetone extracted ^'P''^" '' "°^ feasible by the above method. 



material. The quantity of substitute in the acetone extract was oxidation of the extracted rubber in connection with the 



calculated. The results are shown in the following table: determination of the substitute. 



_ f ■>- T> Some observations were made in close connection with the 



Determination of Suestitlte in Vulcanized Rupber. . . , , . ,-,■,, i j ,-, , 



_ , .. A, .. ,. T- , above determinations of substitute which will be dealt with here. 



Substitute Alcoholic Total , , , , , . , , , j 



Substitut; in Acetone Potash Substitute The acetone-extracted rubber kept in stoppered bottles appeared 



No. Pef c'in" T^"lct. sJphur. ^""T"'' ^'""T"'' '" A +^1"'' to l.e considerably altered after a few weeks. It is remarkable 



2 lo'wMte" S' 39 2 5 i'2 11 '^^* °"'-^ ^^^ vulcanized rubber changed considerably. The 



3 3[ brown '"..".'.'..' 4^3 L8 (i.7 o.i 1.0 change is probably due to oxidation of the rubber. During a 

 S l! brown ".'.!!'. '. 3.8 1.9 o'.l o!3 0^3 previous investigation on the non-saponificability of resins^ it 

 f iJ; brown ••■■.•.•■ ic:9 -d 4.1°(4.0). O.?"].!)'! t4.8Ul)- ^PP«"^d '^at the oxidation products of rubber are soluble in 

 8 10, white in.6 5.2 2.8(2.6) 2.l(0.9)t 4.9(3.5) acetone and saponificable for the mam part. 



10 I; wh°ire" .:::::: 9:t si {:J(o:8) IWoW lia;?) it was demonstrated that the presence of substitmc does not 



11 l', brown 8.1 4.7 0.4(0.2) 0.2(0.4) 0.6 (O.'fi) influence this oxidation and from the analytic results it follows 



12 1, white 8.4 5.4 0.1(0.1) 0.2(0.3) 0.3(0.4) , , , . . , , , . ., " , ^, ,. ,, 



13 without anv 7.8 4.9 0.0(0.0) 0.0(0.4) 0(0.4) ihaX. the determination cf the factis acids musl take place directly 



il_li' *""""" "■'" '-5 ^■- '"■'' '-^-^ after the acetone extraction. 



•The figures between parentheses were found in the mi.xes 7 to 13 after 



having been vulcanized for 3 hours. 'By P. Dekker. "Communications of the Netherland Government Institute 



tSample very finely cut. for Advising the Rubber Trade and the Rubber Industry," Delft, Holland. 



_, . .,,.,, . ,. , , , , -"Communications of the Netherland Government Institute," Part II 



The figures in the third column indicate that the part of the (1917), page 49. 



substitute originally soluble in acetoije retains this property after '^ A. Caspar!. ."India Rubber Laboratoty Practice" (London. 1914), 



, . ..„,.. .. , , r , . ■ , E^ge 123; F. W. Hinnchsen and K. Memmler, "Dcr Kautschuk und seine 



vulcanization. Ihis is true if the samples are further vulcanized, Priifung" (Leipzig, 1910), page 129. 



