PRESERVATION' OF I'ISll NETS. 19 



niLl/s KXTERTMENTS. 



J 



V>\\\\ (1901 ), in Norway, cariitMl on a similar series of experiments, 

 usintr a <]:reater number of combinations, inelndinji^ oak hark, quer- 

 citron extract, anil coal tar. He also carried out more elaborate 

 processes of preparation, inchulin<i: such manipulations as three or 

 four baths and combinations of second treatments. The table follov.- 

 inof gives BulFs results and carries brief descriptions of the methods 

 used. Ill (he text "Bull says he barked the nets in " the custom.ary 

 wav." 



tindeman used the bluestone (or copper sulphate, copper vitriol, 

 blue vitriol, as it is variously called) in the same bath with the 

 tanning material. On this point Bull (1901) says: 



When I befiau tliis investigation, since I used quercitron extract in as pure a 

 condifion as was obtainable, in lieu of catechu, I observed that in solution in 

 water it lias, with copper-vitriol solution, a reaction that produces ;i iirecipitate 

 which dissolves with ditticulty in water, for which reason the coloring method 

 must be re.Lrarded as disadvantajreous, because the precipitate is formed rather 

 on the thiead and is not in the solution. In addition, I found that the second 

 bath may be also hai'mful in the use of very warm (80° C. or 176° F.) solution 

 of potassium bichromate, since this strong agent, with the high temperature 

 used, may very well cause a weakening of the thread. 



Bull also says : 



As a barking material quercitron extract has shown itself to be thV best. 

 * * * A noteworthy result is shown in experiment 17, in which the net is 

 barked twice with quercitron extract and afterwards treated with the oxidation 

 mixture. It is shown that the net. after 11 weeks, is of -the same strength as 

 before it wms immersed in the sea, naiuely, 23 kilograms. 



Quercitron, as well as other tanning extracts and barks, can be 

 secured from American dealers in tanners' supplies. 



The copper may have some preserving action ; Cunningham thinks 

 it is injurious. It appears to the writer that, while it ma}' strengthen 

 the defense against certain organisms, its chief use on nets is to 

 imj)art a dark, durable color. 



