FISH-NET PRESEKVATIVES. 55 



spontaneously, it seems necessary to discover some factor other than 

 tnose that entered into the experiments to account for spontaneous 

 heating of nets. In the case offish nets, water, fish blood, slime, and 

 fish oil, and also sunlight, must be taken into account. Bacterial 

 decomposition might well cause an initial elevation of temperature, 

 but it seems likely that the activities of the bacteria would be arrested 

 and the bacteria killed before a temperature would be reached 

 sufficient to kindle spontaneous heating of the oil. It should also be 

 pointed out, as casting doubt on the belief that spontaneous heating 

 commonly damages nets, that the high temperatures to which lines 

 were experimentally exposed without damage would probably never 

 be reached spontaneously. 



It may also be that the damage done to nets by spontaneous heating 

 is of the nature of supposition without foimdation. That nets heat 

 may be a fact, that they rot is certainly a fact, but that the one causes 

 the other does not necessarily follow. Other and more widespread 

 beliefs than this have turned out to be erroneous. Further investiga- 

 tion of the subject of spontaneous heating will be necessary before 

 positive conclusion can be reached. 



GENERAL CONSIDERATION OF VARIOUS PRESERVATIVES 

 IN LIGHT OF DATA PRESENTED. 



Data have now been presented concerning the effects of 23 pre- 

 serving materials (or combinations and variations thereof) on cot- 

 ton lines, and four on linen lines, with data on the untreated lines 

 as controls. The data concern efi^ects of weather conditions at 

 Washington, D. C; the sea water at Key West, Fla., Beaufort, N. C, 

 and Woods Hole, Mass.; and fresh water at Put in Bay, Ohio, as 

 compared with treated but unexposed lines held as controls. In all, 

 393 samples were measured to length, weighed, treated, measured 

 and weighed a second time, exposed to the elements, and upon 

 return were tested for tensile strength, wearing quality, and stiffness, 

 and notes were taken on fouling, color imparted, and time required 

 for treatments to dry. Where so many data are presented, bearing 

 in so many tangled ways on the practical choice and improvement 

 of preservatives, it will require close study to draw useful and rehable 

 conclusions. All the more so, in that the requirements of nets for 

 different classes of service are markedly different. The different 

 preservatives will now be considered and discussed separately. 



TAR. 



Tar is the most commonly used preservative for fish nets in the 

 United States. Coal tar is used more than pine tar; sometimes the 

 two are mixed. They are usually applied hot, often in a metal vessel 

 by direct heat from a fire, sometimes by the use of steam. The 

 dn-ect heat process applies tar very heavily to lines, stiffens them, 

 and increases weight greatly. Steam tarring applies tar to a much 

 lighter extent, sometimes scarcely more than coloring the lines. In 

 the present experiments coal tar, pine tar, and a mixture of equal 

 parts of the two were studied. The tar was diluted by the addition 

 of an equal volume of benzol and applied cold. 



