12 XJ. S. BUEEAIT OF EISHERIES. 



TANNING MATERIALS USED FOR FISH NETS. 



Up to this point attention has been given to catechu. There are 

 numerous other tanning materials put upon the market as bark or 

 wood or as extract. The extract may be liquid, solid, in lumps, or in 

 a fine powder prepared by a recently developed process. The prin- 

 cipal tanning materials, as given by Cunningham, are : 



Oak bark, the bark of the common English oak, is largely used for tanning 

 leather. The barks of another species in Turkey, and of the chestnut oak 

 (Qiiercus castanca) of America are also used. The bark is stripped from the 

 trees when they are about 15 years old. • 



Hemlock bark is really the bark of a kind of pine abundant in America, 

 called Canadian pine (Abies canadensis). It is the principal tanning mate- 

 rial of the United States. The extract of this material in liquid form has 

 been recommended for net curing under the name of Canada cutch, and is sold 

 in tins containing about 3 pounds weight. 



Mimosa, or wattle bark, is obtained from various Mimosje or acacia trees 

 growing in Australia, where this is the staple tanning material. 



Quebracho is obtained from several kinds of South American trees. It is 

 imported largely in the form of both dry and liquid extracts. 



Valonia consists, not of the bark, but of the cups of the acorns of a certain 

 oak (Quercus cegyJops) growing in the Levant. 



Sumach consists of the leaves of a plant dried and ground. The plant grows 

 in the south of Europe. 



Gambler, or terra japonica, is a dry extract prepared from the leaves and 

 twigs of a tree called Uncaria gambler in the Malay Peninsula. It is imported 

 from Singapore. There are two forms, block gambler, in large masses, and 

 cube gambler, in small, light-yellow cubes. It is not much used for net curing, 

 but I believe has been used in former times at some places, such as Clovelly, 

 under the name of catechu. 



True cutch, or catechu, is a dry extract made from the wood of a tree called 

 Acacia catechu, which grows in India and Burmah. It may be distinguished 

 as Burmah cutch. as its manufacture is carried on chiefly by natives, according 

 to their own traditional methods, in Burmah. It is imported from Rangoon. 

 Until recently it was used everywhere around the British coasts for net curing, 

 and was used in far larger quantities than any other tanning material. 



Red cutch or mangrove cutch is made from the bark of mangrove trees, 

 which grow in swamps at the mouths of rivers in tropical countries. This 

 cutch is now manufactured extensively by two British companies in Borneo, 

 and is largely used for net curing, having replaced Burmah cutch to a consid- 

 erable extent. 



Myrobalans, divi-divi, and algarobilla are raw materials consisting of the 

 dried fruits or seed pods of different trees. They are imported for use in the 

 leather industry, but are not used for net curing. Canaigre is also a raw 

 material, consisting of the root of a plant growing in New Mexico and Arizona, 

 not used for the fishing industry. 



To this list should be added quercitron, a large timber oak (Quer- 

 cus velutina) of the eastern United States, having foliage resembling 

 that of the red oak, but with yellow inner bark. It is on the market 

 as rough bark, rossed bark, ground bark, and solid and liquid 

 extracts. As will be seen later, Bull found this to be one of the l3est 

 materials for curing nets. 



It is thus seen that there are a great many tanning materials, that 

 in common they have tannin, and that this tannin in some way pre- 

 vents rotting of nets, probably by destroying the digestives with 

 which the bacteria seek to rot the net, or by making the thread 

 indigestible. At any rate, actual measurements of strength show 

 that tannins do preserve nets, and that the principal objections to 

 them as ideal preservatives are that if used unaided they wash out. of 

 the nets, and that if the preservation is to last the application must be 

 often repeated. 



