reading without any calculation of the resulting absorptivity and 

 squeezed wetness. Stiffness and shape recovery could be calculated 

 from heights observed at the same time, but the technique required 

 might be too demanding for the results obtained. Even the reading 

 of the volumes in the vessel might require a training program. 



Abrasion or Wear Tests 



The equipment used in the abrasion tests was based on a Paint 

 Washability and Abrasion Machine, Model Number 10$, obtainable through 

 the Gardner Laboratory, Bethesda, Md. This machine (figure 11) is 

 capable of recording 

 the number of times 

 it rubs a sample across 

 a standard surface ei- 

 ther with or without 

 the presence of a liq- 

 uid. It was designed 

 to rub a standard sponge 

 or abrasive block a- 

 cross a painted surface 

 until the paint shows 

 signs of wear, thereby 

 allowing the comparison 

 of paints under standard 

 conditions. The appara- 

 tus and operations were modified for use with sponges by: 



Figure 11. — Abrasion test equipment 



1. Using a standard sheet of wet-dry silicon carbide paper 

 (Tri-M-ite, UOOA grit) instead of a painted surface, and changing it 

 after each set of sponges had been tested. Reuse of the paper gave 

 poor results, 



2. Shortening the stroke of the machine to 10 inches so that 

 it did not run off the ends of the standard-size silicon carbide 

 paper (8% x 11 inches), 



3. Tilting the machine a few degrees so that water could be run 

 across the abrasive surface at the rate of about one cubic centimeter 

 every 5> seconds. 



U. Holding the silicon carbide paper tightly against the bottom 

 of the pan with a metal plate bearing rubbing slots so that the paper 

 did not move and wrinkle, 



$. Modifying the frame, which holds two samples at a time, so 

 that the boxes that hold the blocks bearing the sponges are held loose- 

 ly in the frame. This modification allows the sample to be pushed 

 rather than pulled, thereby reducing the tendency of the front of the 

 sponge sample to dip and dig into the paper. If the sponge is allowed 



U7 



