Calculation of water properties , — The data obtained by the pro- 

 cedure described above were used to calculate the following quantita- 

 tive values: 



A* Water-holding power. This gives the volume of water absorbed 

 as a percentage of the bulk volume of the sponge. Water-holding power 

 is the volume of the sponge divided into 100 times the volume of water 

 absorbed: K^ - 100 W}_/V 



B. Squeezed wetness. This gives the water remaining after pressing 

 as a percentage of the bulk volume of the sponge. Squeezed wetness is 

 the volume of the sponge divided into 100 times the volume of water re- 

 maining in the sponge after the sponge has been subjected to a pressure 

 of 1/2-pound per square inch: Ksw* 100 W r /V 



C. Cleanability. This gives the ability of the user to remove the 

 dirty water from the sponge as a percentage of the water left in the 

 sponge after pressing. It is the volume of water left in the 



sponge divided into 100 times the volume of water squeezed out of it: 

 K c » 100 (W h - W r )/W r 



D. Stiffness, This gives the difficulty in compressing the sponge 

 as a percentage of the height of the uncompressed sponge. Stiffness is 

 this height divided into 100 times the new height during compressing: 



K s . 100 Hg/Hs 



E. Elasticity, This gives the ability of the sponge to return 

 immediately to its original shape as a percentage of the height of the 

 uncompressed sponge. Elasticity is this height divided into 100 times 

 the immediate height after the pressure is released: Ke m 100 H r /Hg 



F. Shape recovery. This gives the ability of the sponge to re- 

 turn, 2 minutes after the pressure on the sponge is released, to its 

 original shape as a percentage of the height of the uncompressed sponge. 

 Shape recovery is this height divided into 100 times the height 2 min- 

 utes after the pressure is released: K sr -, 100 Hr/H s 



Water-test conclusions , — Standard statistical techniques (Snedecar 

 1°U6) were used in arriving at the conclusions that follow on the water 

 tests, 



A, Water-holding power, as shown by table 13* is least for the 

 Anclote Grass and the Hudson Grass sponges. Although the average for 

 the Hudson Grass sponge is higher than is that for the Anclote Grass 

 sponge, the fidicial limits for these two overlap. A superiority there- 

 fore cannot be claimed for the Hudson Grass sponge on the basis of the 

 present size of samples,!/ 



2/Mathematical statistics are based on probability and the larger 

 the number of observations, the greater is our confidence in our con- 

 clusions and the narrower we can set our fiducial limits. We might point 

 out, however, that the mathematics are such that to narrow appreciably 

 the fiducial limits reported here would require much larger samples, 

 which would greatly increase the cost of the tests without adding pro- 

 portionately to additional knowledge, 



Ul 



