BULLETIN OF THK TTNITED STATES FISH COMMISSION. 99 



■wbeii broken sliows a fatty, sliininj;- surface. When in greater masses 

 cate(;lin sliould be close and of tiniforui quality, and have as few boles 

 as possible. Good catechu dissolves slowly in hot water. 



The Association for the Promotion of the Dauish Fisheries has chemi- 

 cally examined 9 samples of catechu, which contained from 12.15 to 

 1S.25 per cent of water, from 77.05 to 83.94 per cent of organic matter, 

 and from 1.10 to 7.40 per cent of inorganic matter. In five of the sam- 

 ples the quantity of tannin varied from 48 to Gl per cent. The retail 

 price varied from (!.V to 9.} cents per pound. 



Catechu is often adulterated by mixing it with potato starch, red clay, 

 sand, alum, &c.* When mixed with inferior catechu or other substances, 

 this may be recognized by the color, which is dark brown, almost black j 

 and by the taste, as it does not have the pleasant sweet aftertaste 

 which is peculiar to good catechu. The adulteration can also be ascer- 

 tained chemically. A solution of good catechu in water assumes, when 

 iron vitriol is added, a green color, while when mixed with other sub- 

 stances it turns violet or black. When earth, sand,t cr similar sub- 

 stances are added to give it a heavier weight, these substances will sink 

 to the bottom when the catechu is dissolved in water, vinegar, wine, or 

 spirits of wine. When the catechu is burned these substances remain. 

 The presence of starch can be proved by a tincture of iodine, which gives 

 the sediment a blue color. After the catechu has been dissolved, first 

 in cold water and then in spirits of wine, the starch sinks to the bottom. 



For tanning with catechu Mr. A. E. Maas, the Norwegian consul at 

 Scheveningen, has given the following directions : One kilogram [24 

 pounds] of the best catechu is dissolved in 40 liters [42i quarts] of water, 

 aini this proportion is observed whatever the quantity of catechu 

 which is boiled. I There must be enough of the solution to cover the 

 nets entirely in the vessel in which they are tanned. Care should be 

 taken that the nets lie as loose and easy one upon the other as possible. 

 The solution is not poured upon the nets until the catechu is entirely 

 dissolved ; and it should be poured over them as hot as possible (about 

 140° to 158° Fahr.), but not boiling. The nets should He in the solution 

 for 24 hours, when they should be taken out and spread to dry. Great 

 care should be observed not to take in the nets until they are entirely 

 dr^'. The solution which remains in the tanning vat is carefully put 

 back into the cooking vat and mixed with water, until there is enough 

 liquor to dissolve the same quantity of catechu as during the first tan- 

 ning, namely, 1 kilogram to 40 liters; and thereby a solution is obtained 



*Dr. Herin.au Kleuke: " Lexilon der Verfalschungen " [Dictionary of adulterations], 

 Leipsic, 1879. 



t Sand is said to make the catechu keep better ; and it has sometimes been found to 

 contain as much as 26 per cent of sand. 



{ Mr. E. de ikauwer, the Belgian commissioner at the Amsterdam Exposition of 18G1 

 says in his report that the liquor must not be boiled but heated to 176° Fahr., be- 

 cause boiling changes the nature of the liquor and makes it corrosive. Kcv. Mr. 

 Loberg, in his book Norges Fifilericr [the Fisheries of Norway], says the same. 



