lOS TTTE ALUMNT JOURNAL " ' 



The lead oxid is used for rnl)l>cr tires and seems to make them 

 more flexible. 



Black rubber contains lani]) black or bone black, the latter being 

 about 75 to 80% tracalic phosi)hate [Ca.j (P04)J and the rest car- 

 bon. 



ANALYSIS OF RUBBER. 



As was previously stated Para rubber contains only 2% oi resin 

 while some African varieties yield up to 41%. 



To get the rubber into a state suitable for analysis is the first 

 thing to be considered. This may be accomplished by cutting the 

 rubber into thin pieces and ])assing thru a very sharp sausage ma- 

 chine ; or better still by rasping tlie sample with a sharp file. 



Resin is determined In- dissolving out the rubber with acetone 

 and extracting the residue in a Sohxlet Apparatus for the resin. 



In the vulcanization varying proportions of sulphur are used. 

 This accounts for the fact that we may have combined sulphur, excess 

 of free sulphur and total sulphur. 



It becomes necessary to separate and estimate each individually. 



Dctcniiiiiiii;^ Free Sulphur: — A weighed amount of rubber is boil- 

 ed with C>o to 70 cc. of $% alcoholic ])otassium in a flask having five 

 or six feet of glass tu])ing connected thru the stopper to act as an up- 

 right condenser. The boiling is continued for five or six hours, then 

 allowed to cool and neutralized with hydrcxdiloric acid (H. CI.) hot 

 I'arium Choloride ( Wn CI.,) solution added and (he sulphur is estimated 

 from the ])recipitate. 



Total Sulf^lnir: — Another weighed (piantity of the sami^le is mix- 

 ed with sodium carbonate, carbon, and manganese dioxide ; placed in 

 a crucible, covered, and heated, very gently at first, gradually increas- 

 ing the heat and continue about one to two hours. Then cool, extract 

 with hot water, neutralize solution with hydrohloric acid, add hot 

 barium chloride solution and proceed as in determination of free 

 sulphur. 



Hard Rubber: — A solution of i)owdere(l (rasped) rubber in 90% 

 benzol should yield a green transparent color if pure. If it is impure 

 the solution will be colored dark brown. 



The presence of tar or ])itch in rubber shoes may be detected by 

 adding some benzine to the sample, producing a green fluorescence. 



Tn the earlier part of Prof. Toch's lecture reference was made to 

 "b^acticc or Oilv Rubber Substitutes'" in which various oils are used. 



