364 



The Philippine Jou7'nal of Science 



1915 



more effective utilization of the material would be very practical. 

 Tan bark is never ground, but chopped v^^ith a heavy, curved 

 knife into pieces about 3 by 4 centimeters in size, which are 

 much too large to permit complete extraction of the tannin. 

 This practice results in a large waste of material, as may be 

 seen from determinations included in Table XV. 



Table XV. — Analyses of fresh and "spent" camanchile bark. 



Condition of bark. 



Moisture. 



On dry basis. 



Total 

 extract. 



Nontan- 

 nins. 



Tannins. 



Fresh 



Perct. 

 10.34 

 12.64 



Perct. 

 34.77 

 23.63 



Per ct. 

 9.41 

 8.31 



Per ct. 

 25.36 

 15.32 



Used 









In this case only 39.6 per cent of the total tannins contained 

 in the bark was used by the tanners, while the remaining 60.4 

 per cent was thrown away in the "spent" bark. 



Undertannage of leather is one of the chief causes of an un- 

 satisfactory product. This is produced in part by insufficient 

 plumping of the hides, in part by the use of coarse bark 

 in making infusions, but principally because of false economy 

 in the use of the bark. In examining the tan liquors in any 

 Filipino tannery, it will be noted that they are uniformly much 

 too weak, except at the very beginning of the process. In fact, 

 the first tan liquors, corresponding to suspender liquors, are 

 the strongest which are used in the process. This, of course, 

 produces rapid tanning of the surface and, to a great extent, 

 prevents thorough tanning of the interior of the hide. 



In determining the percentage of tannin in the tan liquors, 

 specific gravity tests were found to be very unreliable, espe- 

 cially in the case of the older liquors. Large quantities of 

 mineral matter are introduced from the brackish river water 

 and from the hides themselves which are insufficiently delimed. 

 Deliming is rarely effective, as is clearly indicated by the red 

 coloration produced when a drop of a phenolphthalein solution is 

 placed on the surface of the hide. 



A piece of delimed hide just ready for the tan pits, after 

 being placed in river water with sufficient formaldehyde to 

 preserve it, was found to be still well impregnated with lime 

 after forty-eight hours. The specific gravity of the river water 

 itself is 1.029. Table XVI shows the specific gravities of tan 

 liquors at various stages of the process. 



