NET DETERIORATION IN LAKE ERIE 165 



Duroose agrees with findings in other fields, which show this material 

 to be verf effective in preventing putrefaction >ut rather weak as a 

 termicTde The dye, crystal violet, is effective and its potency 

 fS-esed experiment; as yet uncompleted which show that favorable 

 results might be expected from materials of this sort. Dyes can be 

 used when solids such as cuprous oxide or tar, for instance, are so 

 bulky and inflexible as to reduce the -fishing power" ot S^l nets 



It is interesting to note that these experiments show that treat- 

 ments containing^oxidizing agents, such as chromates or alkalie.,^a^^^^ 

 inapplicable to nets. The reason for these results is that alka les 

 destroy the cutin which otherwise protects the cellulose of the cot on 

 fibei from hydrolysis and bacterial attack, thus weakening the fiber 

 and that chromates destroy the fiber by reason of their oxidizing 



^"^Good results were obtained from all treatments selected from 

 those originated by this laboratory and from a commercial preparation 

 whTch Probably consists of copper salts, of napthenic acids. It 



would appear that the method using single ir^^t'^'^tVof'^'the'lest 

 enough to show sufficient differences m the strength of the best 

 preservatives in a short time. Experiments are now being conducted 

 by an employee of the bureau at the University of Wisconsin in 

 order to make the laboratory controlled test more rapid. This is 

 most vahmble since any laboratory procedure which will enab^^^ one 

 to sort out and place various treatments m rank of usefulness, will 

 accompUsh in three or six months what would otherwise take one or 

 ?wo Reasons in nature's laboratory, where storms or other uncon- 

 trollable forces often interfere with or ruin experiments. 



TESTS OF PRESERVATIVE TREATMENTS IN THE LAKE 



A number of racks were wound with samples of treatments selected 

 from those which had previously shown promise ^^^/^f;^;^. ^^^f^^^^^^^^^^ 

 N C These racks were immersed m 6 fathoms of water 4 miles out 

 of' Erie Harbor, and samples removed at weekly mtervals. ihe 

 :Lples were kter broken in the testmg machine and dup We 

 samples were analyzed to see how the copper content of the twme 



^'ThtTnalysis of treated fish netting for copper is not very easy 

 nor is it rapid enough, when using methods Previously ernp^oyed to 

 admit of sufficient samples bemg analyzed so that the results ot tiie 



'th'tw'^hlbts finally evolved and found to be satisfactory 

 was a modification of the Kjeldahl -ethod One foot of treated 

 twine was used for each determination. This was obtained by 

 cu ting four 3-inch lengths from different places m the twine so as o 

 Secu^Tan average sailple. The twme^ was then w^^^^^^^ 

 short lengths, and placed m a Kjeldahl flask, ^rom 6 to » cumc 

 centime'eVs of concentrated sulphuric -^^ was added and the mate- 

 rial was digested for a short period or allowed to stand tor ^ t^^e 

 denending on whether heating facilities were available. Alter this 

 n?elimina?y digestion the flask was cooled, and a very small amount 

 rrSratId nitric acid was ^^ded Treatments c^^^^^^^^^ 

 little tar or those which had been exposed for a long time, requirea 

 liftle of't'e oSdizmg agent; but those wh-\were^ ng. or^ w^^^^^^^^ 

 contained much tar required more nitric a^.d. The flasks were tnen 



