62 



U. S. BITEEAU or FISHEEIES. 



interested in net preservatives have their own and very often decided, 

 opinions on the subject, a statement of the colors produced follows: 



Preservative. Color of treated line. 



Copper oleate Apple green, sky blue, or strong brilliant green, 



depending on concentration of preservative. 



Tar Dark brown or black. 



Copper paint Dark coppery red. 



Petroleum products Black. 



Gilsonite Do. . 



Tanning materials: 



Quercitron and potassium Brown, 

 bichromate. 



Dutch method Dark brown. 



Copper oleate and tar combination Dark brown or black. 



SPONTANEOUS HEATING. 



Fig. 33.— Apparatus used in testing the pre- 

 servatives for tendency toward spontaneous 

 heating. 



Spontaneous heating is com- 

 monly said by fishermen and others 

 to cause the nets to rot. This 

 heating is often attributed to the 

 substance with which the nets are 

 preserved. Experiments along this 

 line have led the writers to suspect, 

 however, that spontaneous heating 

 of nets is caused by something other 

 than the preservatives used. 



APPARATUS USED FOR TESTING. 



The apparatus used for these ex- 

 periments (fig. 33) was made after 

 the fashion of Mackcy's sponta- 

 neous combustion tester. This 

 consits, essentially, of a double- 

 walled cylindrical water bath with 

 a cover carrying two air circulation 

 tubes, a and a'. The sample to be 

 tested is placed in a cylindrical wire 

 gauze or screen, /. A thermom- 

 eter, t, extends into the sample. 

 A second thermometer, f , is sus- 

 pended in the inner cylinder, c, 

 tlirough. the air circulation tube a'. 

 The water in the outer cylinder, w, 

 is then heated to any arl)itrary 

 temperature and kept at that tem- 

 perature for a period of three or 

 four hours. The temperatures of 

 the thermometers, t and t' , are 

 noted at frequent intervals, and if 

 the temperature of t in the sample 

 exceeds that of t' in the air sur- 

 rounding the sample, the difference 



may be taken as heat due to oxidation in the sample being tested. 



