Several attempts have been made to devise a method of determining the cement content of fresh concrete. A few years ago a new concept of such a test was originated by R. A. Willis. To separate the cement from the aggregate, Willis employed a heavy liquid in which the aggregate would float but the cement being heavier would settle to the bottom. The application of this concept to a practical test method was later made by W. G. Hime. The test is now known as the Willis- Hime method. In performing the test, a sample of fresh concrete is secured on the job in much the same manner as for making a test cylinder. This sample is then washed through a No. 30 mesh wire basket by immersing the wire mesh basket in a container of water. After the fine sand and cement mixture has been thoroughly dried, the dry material is then carefully weighed and placed in centrifuge tubes. The tubes are next filled with the heavy liquid (an acetylene tetra-bromide solution) which weighs about three times as much as water. The tubes are rotated and marked so that the volume of cement which settles in each tube can be readily determined. This volume of cement can then be compared with a chart to determine the number of sacks of cement per cubic yard in the original sample. It should be noted that carbon tetrabromide used in the process is toxic. A substitute material is common fuel oil, which is cheaper, readily available, and seems to work well without having any side effects