PUESKRVATION uF FISH NKTi^. 



11 



of insoluble matter, which would ordiniirily be considered objec- 

 tionable. This fact shows that the insoluble matter may add "greatly 

 to the value of the catechu. The reason for this superiority has 

 already been mentioned. The analysis is made by dissolvin<^ sam- 

 l)les of material in cold water. That which does not dissolve in 

 cold water is recorded as insoluble and is useless to the leather tanner. 

 But a great part of this insoluble matter is readily soluble in hot 

 water, and, inasmuch as the nets are treated in the hot solution, this 

 matter is deposited in the fibers and sta^'^s in the nets while the cold- 

 water-soluble tannine wash out when the nets are put to use. 



It will thus appear that analysis of tanning extracts made for the 

 leather tanner's purpose is not all that could be wished from the 

 fisherman's point of view. Cunningham recommends that for the 

 use of net preservers there be included in the usual analysis a figure 

 representing the amount of tannins insoluble in cold but soluble in 

 hot water. 



It might prove to be profitable for chemical manufacturers to go 

 a step further than this by separating commercial catechu into two 

 parts, the cold-water-soluble part suitable for the leather industry, 

 and the liot-water-soluble part, not suitable for leather tanning, but 

 preferable for the preservation of fishing gear. 



With the provision that the hot-water-soluble tannins be considered 

 in making calculations, Henrik Bull's (1912) point may be regarded 

 as important ; that is, that when tanning extracts are bought by the 

 pound Avithout reference to their content of active tannins, very un- 

 profitable purchases may be made. Thus, if a sample of catechu sells 

 for $0.10 per pound, and contains 40 ])er cent tannins, the actual i:>rice 

 we pay for tannin is 10/40, or $0.25 per pound. Further, as will be 

 seen from the following table, the cheaper grades of catechu may 

 (but do not necessarily) furnish tannin at a price considerably higher 

 than would be paid for actual tannin in more expensive grades of 

 extract.* 



Samplr. 



A 

 B 

 C. 

 D 



Price per 

 pound. 



SO. 09 

 .10 



.11 

 .12 



Percentage 

 tannin 

 present. 



Price tan- 

 nin per 

 pound. 



?0. 20 

 .22 

 .20 

 .1S5 



To calculate the actual cost of tannin where an analysis is avail- 

 able, use the formula : 



^ . , . . , cost of extract per pound 



Cost of tannin per poun(l = — — ^ r — ; : — 



percentage of tannin in extract 



that is, divide the cost of extract per pound by the percentage of 

 tannin in the extract, and the (juotient represents the cost per i)oun(l 

 of the tannin. 



" The orisinjil tal>!<' Is in Xorvvejrian 0ro per kiloijram of pxtract. Since, howevor. the 

 tahip is only Intended to represent a comparison, the writer has assuoKHl suitable figures 

 for American readera. 



