60 



WILLIAMS. 



Another process designed by the Deutsche Versuchsanstalt fiir Le- 

 derindustrie u. H. Arnold! (Ger. Pat. 220, 221, Sept., 1908)20 is especially 

 recommended for mangrove extract. It makes use of the action of 

 aluminium amalgam. This process gave a more imsatisfactory result in 

 my experiments than the one mentioned above. Leather produced from 

 it was dark, although of smooth grain. No final conclusion can be 

 reached until a fuller description of the process is obtained. With proper 

 investigation one or more of the three methods last mentioned may con- 

 fidently be expected to prove serviceable for commercial use. 



Table XI. — Effect of vanous metJiods of treatment of cutch. 





Wa- 

 ter. 



Tan- 

 nin. 



Non- 

 tans. 



In- 

 solu- 

 bles. 



Total 

 ex- 

 tract." 



Color of leather. 



Untreated extract 



0.2 per cent NaOH acid- 

 ified with SOo 



AI-1-H2SO4 



0.0 



0.0 

 0.0 

 0.0 

 0.0 



62.8 



53.5 

 55.0 

 59.3 

 58.6 



32.0 



40.1 

 45.0 

 40.7 

 41.4 



5.2 



6.4 

 0.0 

 0.0 

 0.0 



Grams. 



104.0 

 108.0 



Medium red. 



Nearly black. 

 Yellowish brown. 

 Light reddish brown. 

 Medium red. 



Barium aluminate 



Aluminium amalgam — 



^ This is the weight of extract obtained from 100 grams of the original material, 



calculated to the dry weight. 



Dialysis through a suitable membrane suggests itself as a means 

 for diminishing the quantity of metallic salts present. Such a treat- 

 ment is not essential to producing a good tanning material and would 

 be of no great value except in giving a greater concentration of tans. 

 Moreover, the process is an extremely slow one. Two thousand five hun- 

 dred cubic centimeters of a 20 per cent solution of extract were dialysed 

 for thirty hours with a continuous change of water over the diaphragm. 

 The diaphragm was made by depositing a film of collodion on cheese- 

 cloth. It had an area of about 100 square centimeters. At the end 

 of the process only 13.85 per cent of the mineral matter had been removed. 

 The loss of tannin was very small. 



The liquors properly treated, in as great a concentration as it is pos- 

 sible to obtain them in the process of extraction, should be evaporated 

 in vacuo to a solid. Possibly, the earlier portion of the evaporation 

 can be carried out by boiling in tail vessels with converging sides, such 

 as will keep the liquor well protected from the air by a layer of water 

 vapor. However, the last portions of the water must be removed by 

 vacuum evaporation. 



It is not possible to estimate the cost of the equipment for a plant 

 with any accuracy from data now in our hands. The vacuum evapo- 



'" Abstracted in Cherri: Ais. Amer. Chem. Soe. (1910), 4, 2588. 



