FISH-NET PRESERVATIVES. 51 



The results ^iven are for only one application of the preservative. 

 In practice, of course, some preservatives are repeatedly applied. 

 Tar, copper paint, etc., can not well be applied repeatedly, because 

 the accumulating substance increases weignt and stiffness too much. 

 Tanning materials, however, can be repeatedly applied, and it is 

 just these that produce the greatest slirmkage, even on first appli- 

 cation. This shrinkage is to be expected, for hot water is usea in 

 applying them. With repeated .application, shrinkage becomes a 

 ratlier serious objection to tamiing extracts. The copper oleate, 

 being appUed cold in gasoline, produces very little shrinkage. In 

 general, however, one apphcation of any of the preservatives pro- 

 duces little shrinkage. On linen lines none of the preservatives 

 used caused smj measurable shrinkage. 



TIME AND LABOR REQUIRED TO APPLY PRESERVATIVES. 



These factors are, of course, of great importance. Where two 

 preservatives are of the same value in all technical particulars, the 

 one which is less expensive to apply is preferable. It sometimes 

 happens that on off days the fisherman's time is worth little if it 

 can not be employed on his nets and boats, and in large organiza- 

 tions the employees are sometimes without important work to do. 

 In such cases the cost of material is the principal cost of preservation. 

 The cost of copper oleate will be considered elsewhere. 



The time required to apply the several preservatives and for the 

 treated nets to dry may be expensive, especially in busy seasons, 

 when time employed on nets is just so much time taken from fishing. 



Table 24 sets forth the time required to dry the several preserva- 

 tives after they have been applied. 



Table 24. — Time required for application and drying of preservatives. 



Preservative. of^pU- T°*ttimerequired 



cations. ^'j-i^e- 



Copper oleate 1 30 to 45 minutes. 



Pine tar 50 per cent in benzol 1 10 to 12 minutes. 



Coal tar and pine tar 50 per cent benzol 1 20 to 24 houi'S. 



Coal tar 50 per cent benzol 1 24 hours. 



Tanning materials: 



Quercitron and potassium bichromate 3 12 to 18 hours.* 



Dutch method 3 Do.i 



GUsouite 1 24 hours. 



Petroleum products 1 36 to 48 hours. 



Copper paint No. 1 1 No drying required. 



Copper paint No. 2 ; 1 Do. 



Copper oleate-tar combinations 1 20 to 24 hours. 



1 Requires from four to six hours for each application to dry. 



COLOR IMPARTED TO LINES BY PRESERVATIVES. 



All the preservatives studied change the color of the lines. Just 

 what the value of color in a line is and what color and shade would be 

 preferable we do not know. There is a large literature on the subject 

 of color vision in fishes, but results by different observers are quite 

 inconsistent. Still less do wc know oi the reactions of fish to colors 

 that they may distinguish. However, since many people who are 



