232 rilTLLETIN OF THE BUREAU OP FISHERIES 



away germs and partly developed growths and so expose a continually renewed surface, in this way 

 keeping the bottom of the vessel free from life. There is no doubt that when this is successfully 

 done a most valuable composition will result, but the practical difficulties which beset this class of 

 antifoulers must not be overlooked. In order to secure success, the composition must waste at 

 a fairly uniform rate, when the ship is at rest, and also when she is rushing through the water; 

 and this is the more important in the case of service vessels, as in many cases they spend a large 

 percentage of their time at anchor, or in the basins of our big dockyards. If a composition is made 

 to waste so rapidly that it will keep a vessel clean for months in a basin, then you have a good 

 composition for that purpose; but send the vessel to sea, and under conditions where you have a 

 higher temperature, and the enormous friction caused by her passage through the water exerting 

 its influence upon the composition, and j'ou will find that the coating which did its work so well 

 for six months at rest in the basin will, in the course of one month under these altered conditions, 

 be all washed away, and fouling will be set up. Noting this result, the manufacturer renders his 

 composition more insoluble — less wasting — and so obtains a coating which, when the vessel is in 

 motion, scales just fast enough to prevent fouling, and good results at once follow; the composition 

 is then put on the same or other vessels, and they take a rest in the basin, and bereft of the aid 

 of a higher temperature and the friction of the water, the composition ceases to waste fast enough, 

 and bad results at once have to be recorded. (Gardner, 1922-23, pp. 47 and 48.) 



Apparently little consideration has been accorded the fact that all growths that 

 attach to ships have a protective layer of material, frequently of a composition 

 similar to lijnestone, between their bodies and the film of paint, and that in adult 

 forms, at least, food is taken in from a very considerable distance from the sides of 

 the ship. It is apparent to anyone with knowledge of the structure and habits 

 of the animals that cause fouling that the only time a poison carried in a paint film 

 could possibly be effective must be at the time of attachment. 



When it is realized tliat barnacles (which are, as previously demonstrated, the 

 most serious factor in fouling) attach by means of long antennae, and that they do not 

 take any food or even have any functional mouth during the period of attachment 

 (that is, until metamorphosis has been completed) it can be seen that the effect 

 of poison must be either as a direct irritant during this process or else the poison 

 must be in such concentration in the surrounding water that the little organism, 

 after attachment and subsequent metamorphosis, is poisoned by it with the food 

 it takes from a distance of at least 1 inilhmeter from the surface of the paint. The 

 amoimt of poison necessary to build up a concentration sufficient to be toxic at so 

 great a distance, when submerged in an ocean of water that is usually in motion, and 

 to hold such a concentration for a period of weeks or even months, as is demanded, 

 would probably need to be much greater than the amount used. Even as early as 

 1867 Charles F. T. Young questioned the efficacy of poison paints, as can be seen 

 from the following quotation (p. 68): 



"It has been remarked somewhat dogmatically that for protecting iron vessels 

 against corrosion and the adhesion of barnacles the use of a poisonous paint is in 

 all cases indispensable, and this paint must be slightly soluble in water." But he 

 maintains that "The primary requisite qualification for aU paints or patented com- 

 positions laid over the bottoms of iron ships is necessarily the 'preservation' of the 

 iron." 



It is accordingly apparent that the use of poisons as antifouling agents for steel 

 ships has been based either entirely on a priori evidence, without adequate founda- 

 tion, or else is a bold over from the custom of painting wooden vessels, and its 

 efficacious use can be legitimately questioned. 



