The tests on the raw rubber may be carried out (1) on the sample of sheet and crepe as received. For this purpose the rubber is cut into a strip, which is clamped between grips and gradually stretched to breaking-point. The ring testing machine can be adapted for this purpose by replacing the rollers with clamps. As the thickness of the samples to be tested will vary, it is advisable to cut the strips of such a width that the cross-sectional area of all test pieces is the same--say, 40 sq. mm. The method is applicable to both sheet and crepe rubber. (2) Tests may be made as to the behaviour of the rubber during milling or mastication. Small batches are milled under uniform conditions, preferably in an enclosed masticator such as Baker and Perkins supply. The power taken (as measured by the current taken to drive the motor actuating the machine) and the time are recorded. A further test may be applied to the milled or masticated rubber, to ascertain the amount and the time taken to incorporate a finely divided mineral matter, such as carbon black, zinc oxide, or one of the refined clays.[38] The results are not very exact, and the difference in plasticity and dryness noted are usually less than found when working with full-sized machines in the factory. (3) The rubber, either raw or masticated, may be "dissolved" in a "solvent," such as benzene, and the viscosity of the "solution" measured. Generally speaking, the less viscous the solution, the more plastic the rubber. [38] Bulletin Rubber Growers' Association, January, 1921, p. 43; August, 1921, p. 340.