RUBBER. 63 



filter through Hie extraction tube (first decanting off flic <-Ic;ir supernatant 

 liquid) ;ui(l wash with water. Add MII excess of sulphuric acid, lie;il for 

 twenty minutes on the steam bath, transfer the liquid to a separately funnel, 

 shake out with el her, evaporate the ether, and weigh the residue. This 

 weight divided by 0.8 gives the weight of the alcoholic potash extract (fatly 

 substitutes). 



6. Chloroform Extract (Bitumens). 



Wash the residue from the alcoholic potash extract with alcohol and ether, 

 dry in a current of hydrogen or coal gas, extract for three hours with chloro- 

 form, evaporate the chloroform, and weigh the extract. A very small amount 

 of chloroform extract is always obtained even when bitumens are not present, 

 but this is generally not over 1 per cent. 



7. Total Sulphur (Other than as Barium Sulphate). 



To 1 gram of the sample in a 100 cc nickel crucible, add about 2 cc of water 

 and about 5 grams of anhydrous sodium carbonate. Mix thoroughly, using a 

 nickel or platinum rod. Add sodium peroxid in about 0.5 gram portions, mixing 

 thoroughly after each addition. Continue adding the peroxid until the mixture 

 becomes granular and nearly dry, using about 5 or 6 grams in all. Heat the 

 crucible with a very low alcohol or gasoline gas flame until the contents are 

 fused, stirring all the time and carefully avoiding any overheating. (If the 

 material ignites, the determination is ruined.) Allow to cool somewhat and 

 cover the hardened mass with a layer of peroxid to a depth of about 0.5 cm. 

 Heat carefully to complete the fusion and keep the material fused for ten 

 minutes. Cool somewhat, place the crucible in a casserole, and carefully add 

 water. After violent action has ceased, remove the crucible, washing it out 

 with water, make slightly acid with hydrochloric acid, and boil to make sure 

 that any barium sulphate, which may have been used as a filler and was 

 partially decomposed by the fusion, is precipitated. Filter and determine 

 sulphur in the filtrate by precipitation with barium chlorid in the usual manner. 

 This method gives the total sulphur except that present as barium sulphate, 

 and in case no mineral matter other than barium sulphate is present will con- 

 tain no sulphur from the mineral matter. If the rubber contains sulphur other 

 than as barium sulphate in the mineral matter, this will be included in the total 

 sulphur. 



8. Fillers. 



As a rule the ash may be considered as fillers, but if carbon or hydrated or 

 carbonated mineral matter has been used the ash will be less than the fillers 

 and consequently the gum reported by difference will be too high ; on the other 

 hand, the free and combined sulphur is more or less fixed by the amount of 

 mineral matter. An accurate method for determining fillers is much needed : 

 but all methods proposed fail on certain kinds of rubber goods, and frequently 

 the ash determination must be used. For most samples, except hard rubber, 

 the following method is very satisfactory : 



Extract a fresh portion of rubber with acetone; transfer 1 gram of the 

 extracted residue to a weighed beaker of 200 cc capacity ; add 50 cc of camphor 

 oil, and heat on the steam bath until the rubber is dissolved (this usually takes 



a U. S. Dept. Agr., Bureau of Chemistry, Bui. 107, Revised, p. 23. 



