24 U. S. BUREAU OF FISHERIES. 



The accompanying drawing (Barclay, 1905&) represents a plant as 

 used in Scotland for barking nets. Catechu or other extract is dis- 

 solved in tank B^ which is heated by steam from a steam pipe. A 

 system of pipes, the arrangement of which is obvious in the drawing, 

 provides for drawing off the liquor into tanks where the nets are 

 treated. i> is a steam injector or siphon used for convenience in 

 transferring the liquor from one vat to another, or returning it to 

 the dissolving tank. 



It is assumed in these recipes that the nets are perfectly clean and 

 free from oil before tanning. Preferably, nets should be tanned be- 

 fore they are ever used. If they are dirty or greasy they should be 

 washed in warm water and soap, well rinsed in warm water, and 

 dried before tanning. 



It will be noticed from Bull's figures that a double treatment of 

 quercitron extract before mordanting (experiment No. 17) gave best 

 results. If it is desired to do this — and this procedure is recom- 

 mended — the first tan should be much weaker than the second ; that is, 

 use half the total amount of quercitron for first bath, add the remain- 

 ing half to the same liquor for second bath, following with mordant, 

 or after treatment. The net should be dried between first two baths 

 of quercitron. This procedure is in keeping with the practice in the 

 leather-tanning industry. 



While this method is usually referred to in the literature as " Bull's 

 method," it should be stated that an after treatment with a chromate 

 (sodium chromate) was used before; for example, mention was made 

 of it in the article in the Allgemeine Fischerei-Zeitung (1896) re- 

 ferred to, and potassium bichromate in combination with catechu 

 was tested by Lindeman (1897). Olaus Tysk0, in a paper submitted 

 in the Trondhjem contest, states that the method using catechu, copper 

 sulphate, and potassium bichromate had been " used in Fosen for the 

 last 20 years." (Konserveringsmidlers indflydelse paa fiskegarn- 

 straad. Tillaeg til Arsberetning for 1898 fra Trondhjems fiskerisel- 

 skab, pp. 4-7.) 



SUMMARY OF METHODS OF PRESERVATION OF NETS BY TANNING. 



1. Tanning methods are suitable for preservation of nets, leave the 

 nets soft and pliable, and afford a high degree of protection. 



2. Very little increased protection is afforded by treating tanned 

 nets with lineseed oil or tar. 



3. An after treatment of potassium bichromate following the ap- 

 plication of tan liquor greatly increases the preserving power of tan- 

 ning materials, such as quercitron, catechu, gambier, etc. 



4. Copper sulphate (bhiestone, copper vitriol) contributes to the 

 color of nets when used as an adjunct to tanning methods, but does 

 not add much, if anything, to the protecting power of the tanning 

 material. 



5. So far as the data go, hemp threads are protected by tanning 

 materials just as is cotton, but not such a great degree of protection 

 is afforded. 



6. No data have been found regarding the preservation of linen 

 thread. 



