RUBBER BELTING This type, as it is known in the United States, is composed of cotton duck impregnated with a strong, tenacious, slow-ageing rub ber compound. The present methods of manufacture produce a belt, homogeneous, strong, flexible and durable. The rubber fric tion compound is not merely spread on the surface of the cotton duck, but is forced into the pores by massive calender rollers. Therefore the strength of the finished belt depends upon the strength of its duck, and the strength of the duck is proportioned to its weight and its quality. By weight is meant the actual scale weight of a piece of duck 36 in. by 42 in. when dry. These di mensions are known as "U.S. trade standard." The breaking tensile strength of the average 32 oz. duck i in. wide is about Soo lb.; of 28 oz. duck, 44o lb. The duck is first inspected, after which tests are made for tensile strength, crimp, etc. The next step is impregnation of the duck with the rubber compound. Be fore this can be done the duck must be thoroughly dried as the rubber compound will not adhere to a moist surface. This is accomplished by running it over a series of warm plates or heated rollers. The duck, while warm, is then passed through a calendering machine which compresses the rubber compound into it.