10 



U. S. BUREAU OF FISHERIES. 



Since the value of tanning material for net preservation depends 

 upon the abundance of tannins, analyses should support important 

 purchases. The following are analyses made of different samples 

 of catechu, or cutch, by Cunningham, using the hide-powder method : 



Tuan. 



iludah. 



Caller 

 Herrin. 



Tannins per cent. 



Nontannins do. . . 



Insoluble do. . . 



M'ater do . . . 



Total do... 



Strength after exposure pounds; ounces . 



Strength after exposure kilograms. 



46.6 

 20.0 

 11.5 

 21.9 



40.0 

 9.8 

 17.1 

 27.1 



100.0 



100.0 



5;G 

 2.-!37 



8:0 

 3. 629 



45.2 



15.6 



4.8 



34.4 



100.0 



50. S 



14.9 



2.2 



32.1 



100.0 



2; 4 



. 964 



2; 9 

 1.101 



It is seen from the above table that there is a considerable differ- 

 ence between the values of the various samples of catechu, a fact 

 equally true of other tanning extracts. The last two figures under 

 each sample (which the writer has given also in kilograms for con- 

 venience in comparing with the Norwegian figures that are to follow 

 later) represent breaking strenafth. Cunningham explains as follows 

 how these figures were obtained : 



In order to test the actual preserving power of different samples of cutch, 

 I adopted, in my investigations in Cornwall, the following method : I procured 

 a machine for testing the strength of a net before and after the experiments. 

 The principal part of such a machine, which is called a dynamometer, is of 

 the nature of a spring balance. One mesh of the net is attached to the balance, 

 the other at a certain distance to a hook or knob which can be puKed away 

 gradually by turning a handle. As the strain increases the hand on the dial 

 of the balance indicates in pounds and ounces the weight which is equal to the 

 strain until one of the meshes breaks, when the hand shows the number of 

 pounds equal to the breaking strain. 



In comparing the value of the different materials or processes of curing, I 

 took pieces cut from the same net, and, therefore, when new, of the same 

 strength, cured them, then fastened them by mooring at the bottom of Newlyn 

 Harbor. After they had been under water a certain time the pieces were taken 

 up and tested on the dynamometer and found to be of very different strengths, 

 which sho\\'ed the differences in the preserving properties of the various mate- 

 rials or processes. 



One of the earliest experiments carried out on this method proves the pre- 

 serving power of that part of cutch which is insolub'e in cold water. So far 

 as I know, there is no natural cutch or tanning extract which is completely 

 soluble in cold water for the very good reason that the cutch or extract is 

 generally nuide by boiling. But some of the red cutches put upon the market 

 by the Borneo companies are almost entirely soluble in the cold, either because 

 they have been chemicar.y treated or because the insoluble part has been re- 

 moved from them. 



In this experiment I tested four kinds of cutch [as above]. The last three 

 were red or mangrove cutcbes from Borneo. In every case the strength of the 

 solution used was 1 pound t(» 1 gallon of water, the net was dipped twice, being 

 left half an hour in the liquor each time and dried between the two dips. The 

 pieces of cured net were left iinder water, uncovered only at low water in spring 

 tides, for five weeks, and then tested. 



Further reference to the table above will show that the Caller-Her- 

 rin catechu Avhich contained the highest percentage of tannin was 

 one of the poorest in preserving i)ower where the nets were actually 

 exposed for a long time to water and tested for strength. The 

 Tuan catechu was best, though it contained the greatest percentage 



