. The Bell System technical journal . of benzene is added and theparts assembled. After 24 hours or more standing without disturbance,the benzene containing the soluble part of the copolymer is carefully with-drawn by opening the stop-cock very slightly. The weight of the swollengel left on the screens is obtained from the difference between the weightof the assembly after draining off the solution and its original weight. Thisdivided by the original weight of the unswoUen gel gives the swelUng volume(SV) of the material. The slight density correction can be neglected. The dilute solution visc
. The Bell System technical journal . of benzene is added and theparts assembled. After 24 hours or more standing without disturbance,the benzene containing the soluble part of the copolymer is carefully with-drawn by opening the stop-cock very slightly. The weight of the swollengel left on the screens is obtained from the difference between the weightof the assembly after draining off the solution and its original weight. Thisdivided by the original weight of the unswoUen gel gives the swelUng volume(SV) of the material. The slight density correction can be neglected. The dilute solution viscosity is determined directly on 5 cc. of the solutionwithdrawn from the vessel and is calculated from equation (2). The con-centration c is determined by evaporating a known volume of the solutionand weighing the sohd left after evaporation of the benzene. Figure 8shows the viscometers and bath employed for the measurements of therelative viscosity. A variation of the dilute viscosity method adopted for SYNTHETIC RUBBER RESEARCU 37.^. 376 BELL SYSTEM TECHNICAL JOURNAL use directly on latex has been employed as a control during the synthesis ofGR-S^^ This test, referred to as the vistex test, consists in adding 1 the latex sample to be examined to 100 ml. of a solvent having bothhydrophobic and hydrophilic properties, such as a mixture of 70 parts (byvolume) of xylene with 30 of pyridine, or 60 of benzene and 40 of clear solution is run through the viscometer in the usual manner and therelative viscositv used as a measure of extent of reaction. The test has the
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