PRESERVATION OF FISH NETS. 25 



7. All the methods of taiuiinii- impart a dark color to the nets, 

 which color may be advanta<:!:eoiis in making tlie nets less conspicu- 

 ous in the water. 



PRESERVATION OF NETS BY METHODS NOT DEPENDENT ON 

 TANNING MATERIALS. 



The methods of pix)longing the life of nets which make no use of 

 tanning materials, or make use of them only as adjuncts, employ 

 linseed oil, pine tar, coal tar, bluestone, soap and bluestone, salt, 

 smoke, and creosote. . 



Of these, linseed oil and tars are physical protections to the net; 

 they fill up the spaces between the fibers and to a large extent keep 

 the water from coming into contact with the materials of which the 

 threads are composed. Naturally these materials are very efficacious, 

 but that there are many and serious objections to the general use of 

 linseed oil and tar will appear later. Linseed oil will be considered 

 first. 



LINSEED OIL. 



For practical purposes the animal and vegetable oils are looked 

 upon as being divided into two principal groups, the nondrying oils 

 and the drying oils. The nondrying oils, of which coconut, peanut, 

 cottonseed, and olive oils are examples, are used for soaps, foods, 

 lubricants, and the like ; they do not " dry " ; that is, they do not 

 form a skin upon being exposed to air, but under storage conditions 

 may become rancid. The drying oils, such as linseed and men- 

 haden oil, when exposed to air " dry " ; that is, they form tough, 

 somewhat elastic skins, which, when a pigment is incorporated with 

 them, constitute paints. The conspicuous properties of these oils, 

 that is, the turning rancid of the first class, and the drying to a skin 

 of the second, are both traceable to the same cause — oxidation, or 

 absorption of oxygen from the air. Both classes possess a keen 

 appetite for oxygen, and the process of absorption is attended with 

 the generation of heat ; if the oil is distributed in such a Avay that 

 great surface is offered for oxidation and at the same time little 

 opportunity is afforded for the heat to escape, so much heat will be 

 generated as to start a fire, as it is well known that oily rags will do, 

 and also nets. Another peculiarity about this heating is that the 

 hotter the rags or nets become, the faster the oxidation. 



Linseed oil is the great drying oil, used the world over as the body 

 for paints. It has been used in Holland (Barclay, 1904) for many 

 years for preserving nets and to a considerable extent in the same 

 way in England, particularly at Lowestoft and Yarmouth. This 

 method, according to Cunningham, is simple : The nets are given one 

 bath of catechu, thoroughly dried; and then one bath of linseed oil, 

 drained, and dried. After drying, which takes two or three weeks 

 or more, they are again bathed in catechu, which removes any 

 undried oil. In use they are occasionally given a treatment of 

 catechu, like any other net. The method, as used by the Dutch, 

 according to Jessen (1903), is as follows: 



Any grease on the net is first removed in water, to wiiirh a little more than 

 2 quarts of slacked lime is added, per barrel of water. The net is then thor- 

 oughly dried, and introduced into a hath of 18 pounds catechu to 35 gallons of 

 water; the water is boiled and stirred till the catechu is dissolved. The liquor 



