Raw and purified rubber

Raw rubber is in masses or cakes of form and dimensions varying with the quality and origin, often of stratified section and not rarely containing impurities or occluded extraneous bodies it varies in colour from yellowish to brown and has a more or less marked empyreumatic odour D 0-91-0 97 it is highly elastic, but loses its elasticity when cooled to o° or heated to 6o° at about ioo° it begins to soften and it melts at about 180 0 to a blackish liquid, which becomes pasty on cooling but solidifies only after a very long time. 

Rubber is insoluble in water, alcohol or acetone in ether, benzine, benzene, carbon disulphide, oil of turpentine and certain ethereal oils it swells and gradually dissolves more or less completely. 

Purified rubber is in wrinkled or perforated strips, or in blocks, sheet A.c. it. 321 21 

For analysis the sample is taken by cutting strips from various parts of the mass, cutting these again into small pieces and mixing them the outer part should not be used for analysis, since its composition is often different from that of the interior. 

The principal tests and determinations to be made on raw or purified rubber are as follows. 

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