Due to the many variables involved, and due to the different treatment to which the blocks were subjected in Series I as compared to Series II, little correlation appears possible between the results of the two series of tests. It may be observed that the 0.2 inch per 100 feet difference in shrinkage observed between high pressure Modular and high pressure Standard blocks by the authors in preliminary tests is borne out from a comparison of the Series I Group (1) high pressure Modular blocks which exhibited an overall shrinkage of 0.60 inch per 100 feet to the shrinkage of the Series II Group (4) high pressure Standard blocks which exhibited an overall shrinkage of 0.41 inch per 100 feet. This difference of 0.19 in./100 ft. compares favorably with the aforementioned 0.2 in./100 ft. The authors also wish to call attention to the fact that the low pressure standard units made of silica, cement and cinders in Series n Group (4) shrank only 0.51 inches per 100 feet with a curing period of only three days whereas the Seri88 I Group (2) low pressure units made of limestone and cement shrank 0.86 inch per 100 feet with a curing period of 28 days. The foregoing observation suggests that the use of silica in place of cement, within limits, even for low pressure curing, may eliminate some volume change. The authors, however, feel that, since practically all of the variables possible would be introduced in comparing these units, it would be out of the question to assume such a possibility without an exhaustive study of such an idea in which all possible variables except mix were eliminated. Such a procedure would be absolutely essential in order to reach any definite conclusions. The method used for obtaining change in length measurements was suggested by Mr. A.L. Bowling, Chief Engineer, Pre-Shrunk Masonry Corporation of Roanoke, Virginia and has been tested and proven a satisfactory method. The procedure was developed by the authors and was herein proven to be satisfactory and accurate. The idea tor the Series II tests was originated by Professor D.H. Pletta, Head, Department of Applied Mechanics, V. P. I., Blacksburg, Virginia. It is the fervent hope of the authors that the foregoing group of experiments and ideas will form a skeleton or background for an exhaustive subsequent study of the phenomena exposed in these investigations. / M.S.