April 1^, 1889] 



NATURE 



621 



away, and fouling will be set up. Noting this result, the manu- 

 facturer renders his composition more insoluble — less wasting — 

 iiid so obtains a coating which, when the vessel is in motion, 

 cdes just fast enough to prevent fouling, and good results at 

 nee follow ; the composition is then put on the same or other 

 vessels, and they take a spell of rest in the basin, and, bereft of 

 the aid of the higher temperatures and the friction of the water, 

 the composition ceases to waste fast enough, and bad results 

 at once have to be recorded. 



There is no doubt that this is the true explanation of the wide 

 discrepancies which are found between the compositions in the 

 Navy and in the Mercantile Marine : take any of the big lines, 

 their steamers are running at a fairly uniform rate of speed, and 

 the periods of inaction are as short as the desire not to waste 

 the charge on the capital they represent can make them, and 

 under these conditions, by varying the constituents in the var- 

 nishes used for anti-fouling purposes, it is fairly easy, given the 

 necessary data, to so constitute a composition as to secure ad- 

 mirable results ; but when you come to apply this same coating 

 to an ironclad running at various speeds, and as often at rest as 

 in motion, then you at once find that the composition you before 

 imagined to be all that could be desired fails just as lamentably 

 as the tribe of anti-foulers which preceded it. It is not so very 

 long ago that I had the honour to serve on an Admiralty Com- 

 mittee under the able guidance of Admiral Colomb, and, after 

 inspecting many vessels in the Mercantile Marine, and watching 

 all the dockings of Service vessels over a considerable space of 

 time, we were forced to the conviction that it was only in very 

 rare casts that the condition of the bottoms of Her Majesty's 

 ships at all approached the freedom from fouling to be found in 

 the ships belonging to the big companies, with the result that 

 some of the most successful of the compositions in the Mercantile 

 Marine were brought into use in the Navy, and I believe the 

 reports of the dockings since they have been adopted will amply 

 prove the existence of the difficulties I have mentioned. 



Another factor which is often overlooked, and which tends to 

 give misleading results, is the action of brackish water, which, 

 in many cases, seems to exert a special action in keeping the 

 bottom of a vessel clean, the fresh water having a tendency to 

 disagree with certain forms of marine growth, whilst the salt 

 water is apparently equally unpalatable to the fresh-water forms 

 of fouling. 



In most of the compositions now in use, attempts are made 

 to combine strongly poisonous substances with exfoliating and 

 wasting coatings, and this is done by either using metallic 

 soaps, the basis of which is, as a rule, copper, or else by charging 

 a perishable and easily washed-off varnish with poisonous salts, 

 consisting, as usual, of compounds of either copper, mercury, 

 or arsenic, and in some cases all three. 



As I have before pointed out, I do not think the presence of 

 these substances exerts any deterrent action upon the fouling, 

 save perhaps when the vessel is at rest ; but they exert undoubt- 

 edly an important influence upon the rate of exfoliation, as when 

 the perishing of the varnish exposes them they dissolve, or are 

 washed out, and in this way tend to disintegrate and clear away 

 the surface more rapidly — an important and decidedly useful 

 function, but one which might be more cheaply performed by 

 substances other than high-priced metallic poisons. 



The use of metallic poisons of the character indicated throws 

 an increased burden upon the protective composition, as, should 

 the latter become abraded by friction of chain cables, barges 

 alongside, or any other cause, the iron of the vessel will be 

 attacked by the metallic salts, either present in the soluble form 

 in the anti-fouling composition, or rendered so by the solvent 

 action of the saline constituents of the sea water, the action of 

 the metallic salts being to rapidly dissolve portions of the iron, 

 and to deposit the metal which they contain upon the surface of 

 the plates, and these deposits, exciting energetic galvanic action, 

 cause corrosion and pitting to go on with alarming rapidity. 

 Both mercury and copper salts are offenders in this way, but 

 copper is by far the most objectionable, from the fact that the 

 salts formed by the action of the sea water upon the compounds 

 used in the compositions are far more soluble than the corre- 

 sponding salts of mercury, and are therefore liable to be present 

 in much larger quantity, and so exert comparatively a much 

 more injurious action on the plates. 



As an illustration of this, two equal portions of sea water 

 were saturated, the one with copper chloride, the other with 

 mercuric chloride, and into each a piece of steel, planed upon 

 one side, and of about equal weight and size, was placed, and 

 left for four days. At the end of this period the two plates 



were removed, and, after being cleaned and dried, were again 

 weighed, when it was found that the one exposed to the copper- 

 saturated sea water had lost 22 2 per cent, in weight, while the 

 plate exposed to the mercurial solution had only lost 3 "6 per 

 cent., this being due to the much larger amount of the copper 

 salt soluble in the sea water. 



On now placing these plates in clean sea water, corrosion 

 went on in each case with extreme rapidity, and after being 

 exposed for a month, they had both wasted to about the same 

 extent — that is to say, when once deposited on the iron, mercury 

 is practically as injurious as copper. 



I am quite aware that this experiment is not at all likely to 

 be carried out in practice, and none can have a greater convic- 

 tion of the inutility of small laboratory experiments than I have, 

 as they lack all the factors of mass of material and atmospheric 

 influence which play so important a part in a question like the 

 present ; but such an experiment gives one a definite and fairly 

 correct idea of the relative rate of action of the two poisons upon 

 the plates. 



All the time the ship is in motion, the wash of the sea water 

 will prevent the metallic poisons doing the plates or the marine 

 growths much harm, but there is one phase of this question 

 which I think has been overlooked. I need not point out that 

 in certain ports there is a fashion in compositions, and that most 

 of the homes of the Mercantile Marine have some pet local com- 

 position which is largely used at the particular port. If, now, 

 many ships are laying in a basin, taking in and dischai^ing cargo, 

 and if the prevalent compositions contain copper, it is evident 

 that a certain quantity will go into solution in the water, which 

 often does not undergo frequent or rapid change, and under these 

 conditions every ship in the basin will be exposed to the same 

 danger, and wherever an abrasion has taken place in the protect- 

 ives, there copper will be deposited on the iron, causing corrosion 

 and destruction of the plates ; and it must be remembered that 

 when the vessel is next docked and coated no amount of scraping 

 will remove the fine particles of copper deposited in the pitted 

 and corroded portions of the plate, and so finely divided as to 

 be invisible to the eye, but that they will remain and carry on the 

 destructive work under the new coatings of protective. 



It is, I think, a well-recognized fact that, when a vessel coated 

 with a copper compound has become corroded from failure of her 

 protective, or from abrasion, even an entire change of composi- 

 tion does little or no good in stemming the tide of corrosion, until 

 after some considerable period has elapsed, a result which is due 

 to the same cause ; and, inasmuch as copper compositions are a 

 source of danger, not only to the ships coated with them, but to 

 any others which may be at rest in the same basin, I do strongly 

 urge upon the manufacturers to abandon the use of these delete- 

 rious compounds, and to use others equally efficacious and free 

 from the grave objections I have enumerated. 



At the present time, 15 out of 32 principal compositions rely 

 upon copper in some form or other as the basis of their anti- 

 fouling composition, and in one which has enjoyed considerable 

 favour finely divided metallic copper itself is used, and should 

 vessel coated with it, after the varnishes had commenced to 

 disintegrate, be moored alongside an iron ship by a chain cable, 

 or even by a wet hawser, a big galvanic couple would be formed 

 at the expense of serious damage to any exposed iron. 



In the history of anti-fouling many attempts have been made 

 to obtain highly glazed and glass like-surfaces which it was 

 hoped would withstand the action of sea water, and afford no 

 lodgment to marine growths ; but even glass itself is slowly acted 

 upon by sea water, and, when once roughened on the surface, 

 will foul, whilst the rigidity of such coatings, and the straining 

 and cracking consequent on unequal expansion and contraction 

 of the plates and their coating, offers a serious obstacle to any 

 such scheme. 



In concluding this long paper, I wish to point out that in the 

 present phase of the anti-fouling question, and until some new 

 principle for preventing marine growth has been advanced and 

 successfully adopted, satisfactory results can only be insured by 

 an intelligent use of the existing compositions. 



The protective composition is the important composition, and 

 care must be taken to obtain the best in the market, as, if the 

 protection is good, the plates remain uninjured even if fouling 

 take place. The anti-fouling composition to be used with it must 

 either be elastic, or have the same rate of contraction and expan- 

 sion as the protective, and must — at any rate in the Navy — be 

 chosen to suit the work to be done, such as contain copper com- 

 pounds being carefully rejected, whilst preference should be given 

 to those which rely on exfoliation rather than mineral poisons. 



