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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 Af since this is not sufficient to explain the readings by several magnitudes.