Dec., 1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Wallach,’ pinene is converted into limonene by prolonged heating a t 2 5 0 ’ t o 270’. Several experiments were,run in which the vapor of gum turpentine was passed through t h e iron tube heated t o the above tempera.tures for from 2 t o 2 0 hrs., and the material The effect of this preliminary then “cracked” a t 450’. treatment is shown by the boiling-point curves in Fig. 3. The original turpentine which consists largely of pinene is converted into a more complex and higher boiling mixture of which limonene is a chief constituent. There was, however, no appreciable increase in the yield of isoprene upon “cracking” this product by passing i t through the tube a t t h e higher temperature. Activated coconut shell charcoal used as contact material in one run appeared t o have no appreciable effect on the yield of isoprene.
1155
THE AGING OF CERTAIN RUBBER COMPOUNDS’ By I. R. Ruby and Harlan A. Depew RESEARCH LABORATORY
O F THE N E W JERSEY ZINC
CO.,PALMERTON, PA.
Received September 4, 1920
There has been much discussion as t o the relative merits of carbon black and zinc oxide treads for automobile tires. The outstanding objection t o the black tread tire is that, although in the beginning it wears comparatively well, as time goes on the tread chips away a t an accelerated rate.
FIG.3 A-Boiling-Point Curve of Original Turpentine. B-Boiling-Point Curve of Product after Heating a t 250’ t o 2 7 0 ° C. for Time Indicated. CResidue
The isoprene obtained in various runs was diluted with an equal volume of ether, the mixture well cooled, a n d the calculated amount of bromine required t o give the dibromide added gradually, and the reaction mixture constantly agitated. The reaction was very violent a t first but moderated after about one-half of t h e bromine had been added. The mixture separated a small amount of t a r a t first and gradually became darker, but no free bromine was apparent. When fractionated under reduced pressure the resulting product gave a jo per cent yield of a product boiling a t 7 6 O t o 1 0 4 O , under approximately 1 8 mm. of pressure. T h e boiling point of isoprene &bromide2 a t 1 8 mm. is given a:; I O I O . As reported by previous experimenters3 this material has a marked irritating effect upon t h e mucous membrane. Tests after long standing, however, show t h a t the material gradually loses its efficiency, probably by polymerization. This tendency would render i t unfit for use as a lachrymatory gas unless a stabilizing agent could be found. CONCLUSION
Although turpentine is a possible source of toluene in case of an emergency, it does not give, under the experimental conditions described in this paper, a sufficiently large yield of either toluene or isoprene t o make i t a practical source of these products under ordinary conditions. 1 2
Ann., ~ 3 7 282. , Bull. SOC. chim. 131, 38, 989. Chem Z e n f v . , 1899, Part 1, 590
D a y s A q i n q af 70OC. FIG.1
To help analyze this difficulty three compounds, A, B, a n d C, were investigated. Table I gives their composition by weight a n d also by volume. These compounds are typical fast-curing tread compounds, with the exception of A, which contains a low percentage of pigment. Treads in which XX Red zinc oxide is the only reinforcing pigment gen1 Presented before the Rubber Division a t the 60th Meeting of the American Chemical Society, Chicago, Ill.. September 6 t o 10, 1920
