Figure 3 shows the data on a silicone fluid, labeled 12500 cps which gave a high positive normal pressure. Although the tape was run for over 1 hr., a steady state was not reached, and it was concluded that the reason for this was that the back pressure of the manometer was built up from the material fed from between the blocks and this was available at a very slow rate. A system had to be used which did not depend upon the feeding of the fluid into the manometer if measurements of the normal pressure were to be made in a reasonable time. A back pressure was then introduced, and the rise or fall of the material in the manometer indicated which was greater, the normal pressure in the block or the back pressure. By this method it was determined that the normal pressure exerted by a sample of polybutene (molecular weight reported to be 770) was over half an atmosphere. The actual pressure was not determined because the pressure was beyond the upper limit of the apparatus on hand.

The two fluids which gave the small negative pressures were polybutenes with molecular weights which were stated to be 520 and 300. These are fluids which one would expect to be less viscoelastic or more Newtonian because of their lower molecular weight. The maximum suction was 3.25'' of test fluid measured from the top of the block, and steady states were apparently reached with these fluids. It is presumed that this negative head was associated with some geometric factor of the assembly, since different readings were obtained with the same fluid and the only apparent difference was the assembly and disassembly of the apparatus. This negative pressure is not explained by the velocity head ** f since this is not sufficient to explain the readings by several magnitudes.