In the introduction the purpose of the investigation is described which is the development of a method suitable for the determination of the water absorption of crude and vulcanized rubber, and which, in conjunction with ash and nitrogen determinations is especially adapted to the testing of purified rubber. The conditions which affect the results of water determinations are reviewed, with special reference to the formulas of Taylor and Kemp, which make it possible, within certain limits, to compare results obtained by different determination methods. The reasons for selecting the foregoing method of determination of water absorption are described. It is pointed out that water absorption depends to different degrees on the time of vulcanization. In the rubber-sulfur mixture which was chosen, the influence of the degree of vulcanization is small, so that it is sufficient to vulcanize all types of rubber for the same length of time. At the same time it is shown that the results obtained by immersion of rubber for 7 and 25 hours at 80° C. still sufficiently agree with the values computed from the formulas of Taylor and Kemp. A method of measuring water absorption is described in detail. The question arises to what extent rubber manufacturers may use this method, in conjunction with ash and nitrogen determinations, method for estimating the quality of purified rubber. Rubber manufacturers are urged to give their opinion of this proposed method. Some other method will be considered if it should appear that manufacturers prefer this other method.