FISH-NET PRESERVATIVES. 57 



cleaned by it) , experiments were restricted to the treatment of nets 

 with a hot sohUion of quercitron, followed by a treatment with 

 potassium bicliromate, and the Dutcli method. This hitter method 

 consists of treating the net with quercitron and following with a 

 solution of 1 per cent copper sulphate in water, with 3 per cent of 

 stronger ammonia water added. The experiments with quercitron, 

 followed by potassium bicln-omate, were made in order to determine 

 the effect of copper by comparison with the Dutch method. 



Both tanning methods color the lines bro\^=n and by making them 

 hai*sh greatly impair their ability to withstand mechanical wear or 

 abrasion. Also, m their effect on stiffness, there is little difference, 

 both stiffening the lines more than copper oleate but less than any 

 of the other preservatives. They also shrink the lines more than 

 any other preservative. 



QUERCITRON AND POTASSIUM BICHROMATE. 



Where the two methods begin to differ is in actual preserving 

 effect on exposure to water, as shown by the tensile strength tests 

 and also the wearing tests. The lines treated by quercitron and 

 potassium bichromate at all places where tested did not last any longer 

 than the untreated cotton lines. This method was therefore omitted 

 from consideration in the later series. 



THE DUTCH METHOD. 



This method shows much merit. In the Key West, Beaufort, and 

 Woods Hole series — that is, in all the sea-water tests — it had a 

 preserving effect, as shown by tensile strength measurements, at 

 first intermediate between copper oleate and tar. At the end it was 

 still intermediate, though the copper oleate and tar had changed 

 pkaces. The order of tensile strength at first was tar, Dutch method, 

 and copper oleate; later, copper oleate, Dutch method, and tar. In 

 addition to its effect on tensile strength, the Dutch method also 

 prevented fouling almost entirely. 



On linen lines in sea water, where these two methods were also 

 tried, the only preservatives worth consideruig were copper oleate 

 and the Dutch method; quercitron and potassium bichromate did not 

 show any preserving effect. The Dutch method and copper oleate 

 both preserved to about the same extent at Beaufort, the lines lasting 

 about four months' continuous exposure. At Woods Hole copper 

 oleate was considerably better than the Dutch method, though the 

 Dutch method showed merit. 



In fresh water at Put in Bay the results were somewhat surprising. 

 The Dutch method gave excellent results with cotton, easily out- 

 stripping copper oleate as far as tensile strength is concerned. 



The Imen .lines treated by the Dutch method lasted only 60 days, 

 while those treated with copper oleate lasted 90 days and were 

 stronger than the Hnen lines preserved by the Dutch method. 



As appearances now stand, the Dutch method in fresh water and 

 for cotton lines is best; for linen lines in fresh water, copper oleate 

 excels. It must be borne in mind, however, that only one series of 

 experiments has been coJiducted. Before these conclusions are 

 entii'cly trustworthy it will be necessary to carry out many more tests. 



