FOULING OF SHIPS' BOTTOMS 



235 



Table 7. — Resistance (in minutes) of larval barnacles (nauplii) to several concentrations of various 



compounds (from report of A . W. Bray) 



Toxic agent 



Percentage strength of solution 



100 





25 



10 



5 



1 



0.1 



0.01 



0.001 





0 

 0 



1 

 1 



0 



0 



0 

 22 

 10 

 64 



0 



0 



0 



0 

 315 



0 



0 



2.5 

 56 

 30 



0 



0 



0 



5 

 6 

 5 

 14 

 280 



0 



0 



27 

 20 

 13 

 124 



2 

 130 

 84 

 300 



s 



280 

 270 



60-90 

 1 24 

 480 













Copper O-nitro benzoate 









Copper P-nitro benzoate 













Lead O-nitro benzoate 



42 

 82 



89 

 241 











Ferric O-nitro benzoate _ 













Cuprous cyanide 















Cupric cyanide - - . - 



26 

 149 



72 

 313 



94 

 316 

 0 

 25 

 2 

 220 



121 



221 

 516 

 5 



372 



467 





Paris green 









8 







34 



150 



Cuprous chloride .- --- 









Picric acid - 





0 



39 





163 









Zinc cyanide 



18 











Barium arsenate - . - 













Phenyl arsenious oxide 



0 

 0 



32 

 120 



70 



0 

 0 



58 



0 

 0 



270 





3 

 2 



24 

 10 



57 

 23 





Chlor vinyl arsenious oxide 





90 



Diphenyl arsenious oxide .- - 





Diphenyl amine arsenious oxide.. 













Naptnalene - 





105 



























1 Hours. 



Thus, it is seen that Bray has shown that certain compounds have a very toxic 

 effect on the earliest larval stages of barnacles, provided the concentration is sufficient 

 in the medium surrounding the organism to have its maximum effect. It must be 

 understood at this time that the barnacles attach by means of long antennae, and 

 that in the case of mercurial compounds a concentration of more than one part per 

 hundred thousand must be maintained in order to have any effect at all. With the 

 entire ocean as a solvent, and less than 14 per cent of an extremely thin film to act 

 upon, it seems questionable if such poisons can build up a concentration sufficient 

 to be lethal for any considerable period of time. Of course, it is remotely possible 

 that chemical action with sea water might have some effect, as suggested by Gardner 

 (1922, p. 55). He states: 



The toxicity of free substances such as mercury and copper compounds to young organisms 

 does not necessarily give a true indication of their toxicity when mixed with other ingredients of a 

 paint, and the influence of the component parts of the sea water upon the toxic substance through 

 longer periods may render it more or less toxic by dilution or by chemical interaction * * *. It 

 is well known that when two substances are mixed together in varying proportions the resulting 

 mixture is frequently more toxic than the same quantity of either component if used separately. 

 The "why" of this action is not known; it is merely an empirical result. 



However, this type of speculation has no evidence whatsoever for its support 

 and perhaps is indicative of the methods sometimes employed in the preparation of 

 antifouling paints. 



Many paints have been tested by actual application on the bottoms of ships, 

 both by the United States Navy and by the American Society for Testing Materials, 

 through cooperation with the United States Shipping Board. In such tests the vessel 

 to be painted usually was marked off into four divisions, and the forward port quarter 

 and aft stern quarter were painted with the test paint while the other two quarters 

 were painted with the regulation "Navy standard;" or vice versa, as the case might 

 be. In such tests a true comparison of the relative efficiency of the two paints could 

 be determined. 



