October, 1931
IXD USTRIAL A.VD EXGILVEERIh’G CHEiIfIXTRY
__
1093
Preservation of Textile Fish Nets‘ A. C. Robertson C H E Y I S T R Y D E P A R T M E N T , U K I V E R S I T Y OF ILLINOIS, U R B A S A , ILL.
Few of the old-time net preservative treatments are HEN ancient man being used, particularly by effective. The number of really effective newer treatfirst f o u n d a fish salmon and tuna fishermen. ments is small, and few of these are really economical left helpless in a The fishing power of a net in actual fishing practice. The choice has virtually pool by the descending tide, is a property difficult to evalunarrowed to two types of net preservatives. A n exhe no doubt made a meal of ate; recEnt e x p e r i m e n t s ample of one is a 25 per cent solution of copper resinate the godsend, and, thinking tend to show that color is a in water-gas tar oil. This is used for treating gill nets later of the pleasant experiminor factor in some cases. which must remain flexible to maintain their fishing ence, reasoned that perhaps However, the tenture of a net power. The other typical net-preservative formula is an important quality. It he could make pools to catch is a paintlike dip containing 5 ’ / 1 per cent finely divided more fish. This he did, for has been found that if the cuprous oxide in suspension. This treatment is for weirs or dams are known to be wings leading to a trap net trap and pound nets which need not be flexible and among the most ancient of are stiff, the net is more effecrequire a certain amount of armoring to resist friction fishing devices. Brush weirs, tive. Gill nets, on the other and to divert fish into the pocket of the net. The cona form still used in the Maine hand, need to be flexible, for centrations noted previously apparently represent the sardine fisheries, pro b a b 1y if the fish senses an apprecimost economical concentrations of toxic. More active able resistance, it will not go came next and woven nets material increases the cost unduly, and less active last. Hand lines, used with into the net far enough to material endangers the safety of the net over the usual hooks or as snares, probably have the twine slip over the working periods. Indeed, if the working period can be came into use a t the same time head and under the gills. It shortened enough, simpler, cheaper treatments are is for this reason that linen and were coincident with the available. is so largely used for gill nets. development of the textile art. The difference in physical properties of different Linen possesses considerable The manufacture of nets in types of nets has made impractical the evolution of strength and flexibility, its a n c i e n t t i m e s a n d among any universal net preservative. loosely stranded thread allowprimitive peoples is developed ine: it to flatten under load to a surprising degree. One may find in museums fragments of Egyptian nets which are and slip under the gill covers in mucuh the same way that a knife much the same as modern nets. The twine is not as regular would. Cotton threads, on the contrary, must be “cablenor as small as that used today but the workmans’hip is quite laid” to resist wear properly, and as a result do not gill fish as as good. It is indeed startling to note the regular mesh of a effectively as thread made from bast fibers. However, cotton net and its fine appearance and then to compare its relative thread is cheap and, since nets made from linen are often torn merit with the quality of the crude tools and weapons which its by storms and debris just as much as the weaker cotton ones, linen thread is not used as much as its superior fishing makers used. While the art of net weaving reached a high state of de- power would warrant. It seems that the salmon fisheries are velopment long ago, the art of preserving fishing gear did the only ones where the low cost of cotton does not make up not attain a similar position. Nets have always been sub- for the superior fishing power of linen thread. jected to many hazards and usually lead a short life. Not Value of Netting and Need of Preservatives only do powerful fish, sharks, and seals entangled in a net The annual catch of fish in American waters is approxiescape easily and demolish it, but floating debris often tears holes in a net or pulls it adrift. Storms effect even worse mately 3 billion pounds, worth about 109 million dollars to damage, especially if the net is fouled with marine growths. the fisherman. Nearly 16 million dollars worth of gear is I n addition to the damage caused by these external and used in catching these fish. Table I indicates the kind of obvious agencies, a net is constantly losing strength by reason gear, its value, and the relative amount of fish which it of normal routine use. The oil and slime from fish cause the catches. It is interesting to note that lines catch relatively net to “heat” when it is deposited in a heap in the hold of a much more per dollar of gear than do pound nets and traps. fishing vessel, and there is always a weakening influence which T a b l e I-Types of Gear for C a t c h i n g F i s h (4, IO) is apparently due to the action of the water. It has long RELATIVE RELATIVE V A L I J E OF TONNAGE OF been suspected that the general weakening of nets was due GEAR VALUE GEAR CATCH to bacteria and a recent study (5) of the deterioration of Dollars % % nets in fresh water showed that certain cellulose-digesting Seines 2,253,134 13 30 Gill nets 3,475,289 22 10 organisms were indeed to blame. The hydra (red slime) Pound nets, traps. weirs 7.654.490 48 17 629,182 4 18 which the fishermen dreaded so much were found not to be L i n e 3 Other pear 1.985.135 13 25 guilty. Total i5,997,210 K O E O As a result of the agencies enumerated, nets deteriorate very rapidly. Old-time fishermen tried many remedies, It can be seen that the expense due to nets is a heavy one, some of which still survive. Tanning with bark and treating for their value equals about one-fifth of the gross value of the with wood smoke were two popular methods. The preserva- catch. In addition t o this, there is the additional expense tives derived from both bark and wood smoke are water- caused by nets needing replacement. According to a Census soluble and hence do not protect a net which is immersed for a Bureau release in 1928, $5,401,173 worth of webbing was made long time. The bark does give the net a good color, thus in the preceding year. When the value of the ropes, twine, increasing its fishing power; consequently this substance is still floats, and sinkers used in conjunction with this amount of webbing is taken into account, an estimated value of $10,1 Received Ma) 5, 1931.
1094
I N D USTRIBL A N D E’XGILVEERIXG CHEMISTRY
000,000 is obtained for the yearly depreciation of nets in America. This value agrees well with one obtained by assuming an average life of one and one-half years for the $16,000,000 worth of gear now in daily use. 4 Tariff Commission Survey (11) states that the cost of gear on Lake Erie is 14 per cent of the total fishing cost. The corresponding figure for the Lake Superior fisheries is 22 per cent. Any reduction of these relatively large fixed expenses is sure to be welcomed by the fishermen. Early Experiments Until Taylor published a revien- (6) of the literature in 1921, the only work in English upon net preservation was Cunningham’s paper ( 2 ) written in 1902. Subsequent work in this field has emanated largely from the laboratories of the U. S. Bureau of Fisheries. This organization has published the only long series of work upon net preservation and is still engaged upon this work, which is in a way peculiarly adapted to governmental research. The reason for this is that there are in this country many types of gear used in diverse localities which no individual could hope to reach. A federal bureau can reach these distant regions and, in addition, can work more leisurely than a private organization, which is a powerful advantage in a field of investigation so subject to chance and fluctuating conditions. Also in order to avoid errors, several years’ observations upon hundreds of samples should properly be used. Although the Bureau has been obliged to limit the number of samples studied, it has avoided error better than private agencies, for, with the exception of copper paints, no proprietary article tested thus far has equaled the net preservatives developed by the Bureau. Many of the older methods of net preservation are described by Taylor (6). This investigator suggested the use of copper oleate in nonaqueous solution, which is an improvement upon the treatment used by Sardinian fishermen who dipped their nets successively in copper sulfate and soap solutions in order to preserve them and to make them blue in color. The U. S.Bureau of Fisheries tested copper oleate as a net preservative and found it very efficacious. I n 1921 the Bureau recommended the use of copper oleate and manufacturers began marketing it in a few months. Unfortunately some lots of this material were low in copper content (8 per cent copper is deemed a practical concentration), and other lots contained an excessive amount of oleic acid or some other material which affected the nets adversely. It is not probable that similarly inferior material will be offered for sale again; nevertheless this episode has done much to impede the progress in the field of net preservation and to make fishermen skeptical of new types of net preservatives. It is estimated that 60,000 to 100,000 pounds of copper oleate were used by fishermen in 1923. It was found in 1923 (9) that finely ground cuprous oxide gave excellent results in treatments for net preservation. A number of tests had confirmed the value of this material and steps were taken to perfect a useful mixture which could be made by individual fishermen if they so desired. Cupric oxide, strange to say, is almost useless as a toxic material. The reason for this is not evident a t present, nor is it clear why the red oxide can dissolve to give cuprous ions in sea water. A paint pigment ground so fine that 98 per cent would pass a 350-mesh sieve and consisting of a t least 88 per cent cuprous oxide was found to be the most satisfactory material to use. Materials more finely ground did not appear to possess superior qualities. To give the best results, this so-called Navy Standard pigment should be associated with about 20 per cent of tar to act as a vehicle. Various solvents were tried, and i t was found that kerosene gave excellent penetration of the pigment. Fish oil helped the formation of a homogeneous mixture but appeared to diminish the strength
Vol. 23, No. 10
of the twine. Benzene and carbon tetrachloride proved to be no better than kerosene as solvents. Pine oil was found to be an excellent solvent and seemed to contribute some prrservatire action of its own. TT’ater-gas tar oil was also found to be excellent and, in addition, relatively cheap. A study of the results of these experiments led to the adoption of a formula which has proved yery useful ( I ) : 5 5 pounds Navy Standard cuprous oxide pounds coal t a r pounds wood t a r gallons water-gas t a r oil
12 6 9
Mixed tars are used as a vehicle for the sake of their physical properties. Trinidad asphalt or even petroleum asphalt may be used as a vehicle, but these materials are not as effective as a coal tar having small quantities of free carbon, or rather, material insoluble in benzene. The use of fuel oil, which is suggested by its low price, has not shown itself to be of value. Some crude water-gas tars are worthy of consideration and may replace the solvent and part of the vehicle in the previous formula with a consequent saving of money. One tenth per cent mercuric oxide may also be added to the formula. Ferric oxide, burnt umber, or silex are without particular value but are sometimes added as diluents. One commercial treatment apparently contains “Prince’s Metallic” pigment as a diluent. These additional substances appear to be without particular value when added to the formula, which seems to represent nearly optimum roncentrations and physical properties. Before the cuprous oxide formula was evolved, the effects of numbers of chemical agents were tried in an attempt to pre.serve the fibers of fish nets against deterioration. One series of attempts was directed toward changing the surface character of the cotton fiber. Zinc chloride was used in the hope that the smooth hard coating of hydrocellulose thus formed would be resistant to bacterial attack, but the results were unpromising, as were those obtained by mercerizing the twine. The application of graphite was also fruitless. Attempts were also made to poison the fiber by precipitating toxic substances in or upon it. Copper soaps formed in situ proved to be somewhat useful, but the protective substance is deposited almost wholly upon the surface in relatively large fragments which soon become dislodged. Copper ferrocyanide treatments are open to the same objection. In addition the ferrocyanide is probably too insoluble to be very toxic. Salts of lead have been tried as toxics. Lead chromate was used because the precipitate has good physical properties, but the treatment has failed to protect the fibers. The reason is no doubt due to the oxidizing effect of the chromium. F’arious tannins have been used as preservatives. Because tannins contain substances soluble in hot water and relatively insoluble in cold, fibers can be given a coating by dipping in a hot solution of these materials. They do not, however, preserve nets in this country as well as would be expected from the results recorded in the literature. The reason, no doubt, is that conditions in Scandinavian waters, where tanning treatments have been found effective, are not as severe as those encountered in fisheries of this country. A number of petroleum products were tested during the earlier experiments at the Bureau of Fisheries. Though they produced physical properties resembling those given by tars. they failed to protect the netting. Solutions of gilsonite were also tested a t this time and found to be worthless. The material apparently contains no toxic substance and loses its desirable physical characteristics after a short immersion in water. Nevertheless, in 1928, the writer found preparations made of this material still being sold and recommended very highly on Puget Sound, a n evidence of the power., of salesmanship over those of observation.
October, 1931
I S D U S T R I A L , A S D EL\-GINEERIA'G CHEMISTRY
dzulniic acid, a dye, was tested and found to be of little value. Combinations of rare earths with copper oleate have no added value. Later Esperiments
COST Co.lrpsRIsoss--~~lienthe writer joined tlie Bureau nf Fisheries in 1927, the art of net preservation had been placed on a reasonable basis, quite different from the empiricism which had characterized it before 1900 or owen 1920. The experiments which accomplished this end were due to the wurk of' Taylor and others ( 6 , 7 , 8). The work thencefort'li logically resolved itself intn extending the tests upon promising formulas and into comparing proposed treatments with the older time-t'ested ones concerning n-hich so many data mere available. Mureo\.er, it seemed best to compare preservatives upon a Imis of equal cost, and accordingly the concentrations of the preservat'ives to be tested were chosen upon that basis rather than upon one of equal concentrations of toxic material, etc. As an example of this work can be taken the performance of a mixture containing 0 . i 5 per cent mercuric oxide plus fiper cent ferric oxide, whicli was used t'o replace the cuprous oxide in the formula giren earlier in the paper. It was found that this treatment was nearly as effective as that containing an equal cost amount of cuprous oxide for use in the fresh water of Lake Erie, but nearly worthless for use in .ea water. The solubility of mercuric oxide probably was t,oo great in sea water. Attempts t o decrease this effect by substituting mercuric sulfide were fruitless, apparently because the latter compound is altogether too insoluble. A few tests xvere made with mercuric soaps. The results showed that these materials are not mmoniical ones to use on a basis of cost. TESTSON K E W~lla~rErir.~I.s-Severalwar gases were tested in the form of solutions in coal tar. Among them was diphenylchlorarsine, u s c ~ lin a concentration of 0.2,; per cent. This material offers little p m i i s e for use in net preservation in contrast to reports of success in treating marine piling with similar toxics. Large concentrations of this niatwial could not be used becaiise of the possible chance of irritating the fishermen's hands arid tlie danger of poisoning the men theniselves from the arsine nliicli might be produced by reducing organisms present i i i the water. Experiments were not continued further, since past studies of the mechanisni whereby higher organii;nis are poimied with arsenicals of the wargas type indicate that there will be sniall hope of success in killing or inliiliiting the growth of the simpler marine forms which lodge on n e t t i q . In ansn-er to some criticim concerning tlie properties of copper oleate, a number of analogous copper compounds were tested. Copper resinate was found to be more effective than oleate in preserving the nets. ;In excess of resin, moreover, is not deleterious in contrast with the bad effect of an excess of oleic acid. Copper resinate is also brittle and sticky, wliile copper oleate is soft and slippery and causes trouble by allowing knots t'o slip and widen the meshes of the net. If the individual fisherman deems copper resinate too stiff or wiry, he niay substitute some copper oleate in the mixture used for treating his gill nets anti therrl~ysecure almost any texture he desires. A Danish preparation, presumahly consisting of copper iiaphthenate in concentrated solution, is quite effectire. A copper soap made from an American petroleum product was tried t o see if it w-ould serve as well. It is inefficient a t the price asked for it a t present, and is also somewhat too slippery. S o doubt' the copper salt of any saturated organic acid with a molecular weight of m e r 200 and a price less than that of oleic acid can be considered for use as net preservati\.e. However, resin acids compose about 90 per cent of rosin; since the price of this material is so low, copper resinate no doubt will
1095
continue to hold its place as an economical net-preservative agent. EYPERIMENTS AT LAKEEnrE-It was possible to conduct some important investigations at Erie, Pa., where the cobperation of a local fishing company permitted the production of very valuable results. S e t s treated with preservatives were actually used in practice. The result showed that the local fear of nets darkened by treatment ("nigger nets") was unfounded. The data from this test are presented in Table 11. T a h l e 11-Catches
w i t h Test N e t s , July 19 to S e p t e m b e r 9 GANG 1
GANG 2
UUTRE.4TED TREATMEKT UNTREATED T 4 R -~-~ Krnnsm.~ 2850, COKTROLS, CONTROLS, TREATMENT. 'A'HITE NETS BLACKh-ETS WHITE h - E T S BLACKNETS S e t 1 N e t 3 Net 3 Net 4 N e t 1 N e t 2 N - t 3 N e t 4 233 250 224 181 229 229 245 227 32 27 15 3; 1; 2; lz 22 16 4 i 13 12 9 8 13 11 14 16 8 4 3 2 2 4 4 3 - - - - 308 309 255 215 284 2 5 2% 3 % ~~
FlsIi
Herring Blue pike Whitefish Burbot Perch Total
A\..
~
:g
308
233
278
282
It' seems that the only marked difference between the catch of the various nets is to be found in the number of whitefish and burbot taken by the nets treated with preservative 2850. This difference between the dark and light nets for gang 1 seems large enough to be called significant, but the nets of gang 2 show very litt'le difference. Kheii one considers that fish run in schools n-hich often hit nets in irregular groups, it seenis reasonahle to conclude that both gangs show substantially the same catch and that treated nets can safely be used for herring fishing in Lake Erie with no danger of decreasing the catch, except' that fewer whitefish will be taken at' the same time. From tlie viewpoint of statistics, these tests contain too few observations to a h v it to be said that there is really a significant' difference in the catches. However, the data are exceedingly ubeful from a practical viewpoint, because local opinion predict'ed total failure for the dark nets. Treatment 2850 consisted of 3 pounds of coal tar, 6 pounds of pine tar, and G pounds of cuprous oxide in 5 gallons of wu-m kerosene. The supernatant fluid \vas used, the sludge containing tar and heavy particles of cuprous oxide being discarded. The tar-kerosene treatment' consisted of a sludge-free solution from a mixture of 1 gallon of coal tar and d galluns of kerosene. Treatment 2850 was extemporized hurriedly in the field from materials available a t the time it became possible to conduct the fishing test. This extemporized treat'iiient ser\.ed its purpose well, and sliowed the fishermen that the use of t'reated nets is practicable. Better treatments can be devised and tested for resistance to deterioration, now that the question concerning the fishing power of dark nets has been shown by t'ests under actual mrking conditions. Another point investigated was the role played by the various types of fouling. The effect of red slime was first studied, since the fishermen deem it so troublesome. During the summer, certain species of hydra become very abundant in Lake Erie, of which one with a red color is most common. These small animals drift about the lake, stinging the fish and driving them wild. The hydra settle upon the nets where they remain as a source of annoyance to the fishermen, Tvhose hands often swell as a result of the irrit'ation caused liy handling nets thus contaminated. This red slime represenk practically all of the actual grcss fouling that affects nets in Lake Erie. The growth of algae, the green organisms found in nearly all waters, is generally not very great, though often a factor to be considered elsewhere. The amount of grass and Jveeds is not a t all comparable with tlie growths found a t Beaufort, S. C., for instance, where luxuriant growt-ths occur during warm n-eatlier.
IO!&
I.~ocs?'lzI.11.A31) EA-Gl3f$EIZl.Y(: ('lIl$;.Ml&Y,rfiY
The fisliwinen idieve that this rcd slime rots the nets. lIowcver, rr.11eu m e considers the mode of life uf hydra, this does not seem probable. I t was thought that piasildy formic acid or a similar product caused the hydra to "sting," and that, this acid might Iiydrdyze the celliilose of the cottrai.
Tire tnicroscopic exa~iiiiratioriof the twiw showed several iiiteresting phenomena which led tu tats of new textiles and iiew types of prrserr:itivc t,reatnrent. It was noted that when t,lie tensile strength (if fibers began to decrease rapidly, the liacteria at the same time had entered the lumen of tile cotton film, and tliut the two events weresimultonrous. The fibers began to swell rapidly after th .vntry. 1 T h e swelling was accompanied by a quick i w w t l r
