22 U- S. BUREAU or FISHERIES. 



Lime may also be used as a mordant or fixer for the tanning ma- 

 terial. The lime is applied in the form of a solution as follows : Add 

 slacked lime to water in a large container, and let stand with occa- 

 sional stirring for several days. The clear liquor that remains after 

 the excess lime has settled is to be applied to the nets in lieu of the 

 potassium-bichromate-ancl-bluestone solution in the method to be 

 given below, after they have been barked. No measurements of the 

 strength of nets so preserved have been found. 



A rather elaborate process of tanning employing lime fixation is 

 described in an article in Norsk Fiskeritidende (1886). A transla- 

 tion of this article by Herman Jacobson was published in the Bulle- 

 tin of the United States Fish Commission (Vol. VI, No. 7, June 12, 

 1886, pp. 97-104). The method consists of three applications of 

 catechu, one of lime water, and a final treatment of a mixture of 

 Stockholm (pine) tar and coal tar. That method appears to be too 

 elaborate for use in the fisheries of to-day. A point of value in this 

 paper, howeA^er, is that where more than one bath of the tanning ex- 

 tract is used the first one should be much weaker than the others. 



IMPROVED RECIPE FOR TANNING NETS. 



This section of the paper, treating preservation by tanning ma- 

 terials, is to be concluded with a recipe regarded as the best, and a 

 summary. The recipe, given by Bull (1902), is: 



To 220 pounds of net (cotton or hemp, the method is best suited to cotton) 

 talie 33 pounds of solid extract of quercitron, or 143 pounds of oalc hark. (Cate- 

 chvi does not give such good results, but if used, take 53 pounds.) 



The extract is boiled « until dissolved in 130 gallons of water. Stir con- 

 tinuously in the vessel to prevent the extract from burning to the bottom ; the 

 warm solution is poured over the net, which is laid in the vessel. Witli a flat 

 board, if necessary, push the net down under the liquor. Cover the vessel well 

 with a tarpaulin or sail canvas so that it can cool oft only very slowly. After 

 the vessel is completely cooled off the net is taken out and as nuich of the water 

 as possible is wrung out before beginning the after treatment. If this is done 

 at once, without preliminary drying, some of the tannin will dissolve out and 

 the net will lose. 



The after treatment is carried out as follows : To 220 pounds of net take 

 2i pounds bluestone and 8^ pounds potassium bichromate, and dissolve them 

 in 1.^0 gallons of cold water.'' After the substances are entirely dissolved and 

 the whole stirred well, the net is put into the bath. It is best to move the net 

 about in the liquid from time to time so that it works evenly on tlie entire net. 

 In this bath the color of the net is much darkened ; if quercitron is used a 

 uniform brown color is produced, like that of a barked net that has been used 

 a long time. After two hours the net is taken out. 



It is the safest plan now to wash the net in water^ — for example, by putting 

 it in a tub — but perhaps this is not necessary, so it can be spread out at once to 

 dry, or be taken aboard. The water from the after treatment is quite worth- 

 less, for the salts added have been completely used up. 



By way of comment it may be remarked that tlie best way to dis- 

 solve the extract is to put it in a coarse bag and to suspend the bag- 

 in hot water. This prevents debris from going into the solution. In 

 heating the large amount of water the exhaust steam from an engine, 

 or any other steam of a pound or two pressure may be used. 



" The advisability of boilinj? the tan liquor is disputpd. It appears the safer procedure 

 to heat the water during the process of dissolution of the extract to about \~rt° F. 

 (80° C). 



<> Blueston(> attacks metal vessels, and it should, therefore, be dissolved in barrels or 

 other wooden vessels. 



