Abstract
In conclusion, it is shown that the “Delta A function” provides an instrument for the classification of carbon blacks as regards their usefulness to the rubber compounder. It is an index of widely inclusive character and not only indicates performance at optimum concentration, but also the range of effectiveness. The writers have undertaken exposition of the special applications of this to the classification of carbon pigments, pointing out the precautions necessary for its accurate use. We believe it important to supplement the “Delta A function” with other stress-strain data, also with laboratory performance tests, and finally with service records, when it is necessary to differentiate between carbons of the same general category. On the other hand, we believe no study of carbons or other pigments is complete unless “Delta A” values are included. Acknowledgment is gratefully made for the valuable suggestions of W. B. Wiegand and also the cooperation of Binney & Smith Co., who supplied all of the carbon blacks investigated and gave permission to publish the data covered by this paper.
