Abrasion results , — The data are given in figure 12. In this 

 figure, the length of the line represents the spread of values that 

 are characteristic of the given sponge, within the probability chosen 

 for statistical analysis. Since the data were not as accurate as were 

 those for the water tests, an 80 percent probability limit was chosen. 

 In other words, there is only one chance in five that any average 

 sponge of the particular grade chosen will give abrasion losses out- 

 side of the range depicted by the line on figure 12 for that sponge. 

 The maximum loss of any sample tested was less than 2 grams from a 

 sponge sample weighing U*lt- grams. Most of the sponges showed a loss 

 of less than 1 gram. 



Conclusions on abrasion tests , — More work is needed to correlate 

 the abrasion test with types and grades of sponges. Although there 

 are some trends in the data, this test cannot presently be used to 

 predict sponge wear in actual service. 



The main trend appearing in the data is for the relatively stiff 

 sponges — Florida Yellow, pale Anclote, and pale Hudson — to give the 

 least abrasion loss, and for the loose-structured sponges — Inshore, 

 Deepwater Mediterranean, dark Hudson, and dark Anclote — to give the 

 most abrasion loss. So few Florida Key aniCuban Sea Wool sponges 

 were available that no conclusions can be drawn regarding them ex- 

 cept to say that neither gives high abrasion losses. Aside from the 

 relation to variations in bulk density (stiffness and looseness), it 

 appears that the fine structure of all of these sponges has about the 

 same rate of wear. 



The test does not reveal a consistent progression from No. 1 

 through No. U grades of sponges. The explanation for this fact is 

 that the distinctions between grade numbers have been on the basis 

 of faults that would not have much effect in a small sample. Further- 

 more, Forms differ from Cuts mainly in shape, which difference also 

 would not become evident in the small samples used in this test. 

 Thus, a more realistic wear test should be based on using the whole 

 sponge, rather than on using !§•" x l^" x 3§" samples, so that such 

 defects as large holes and weak inside structure would have more 

 chance to affect the results of the wear test. Bulk density also 

 is worthy of investigation. 



Cleanliness Test 



On the basis of studies reported in table 19 (page 57), it is 

 felt that no natural sponge should contain more than 10 percent of ma- 

 terial that can be removed by thorough washing. Since the determina- 

 tion of the amount of material removable by washing requires the use 

 of an analytical balance, in most cases a qualitative test may have to 

 be substituted. The following is suggested: Dampen the sponge with 

 a mi nl nn-im of water and do not rinse. Squeeze out a few drops onto a 

 piece of glass. Reject the sponge as unclean if the drops appear to 

 be milky against a dark background, or if on drying, the plate shows 



U9 



