TANNINS FROM WATTLE BARK. 
2. Satisfactory results are not always obtained by tanners who grind their 
own bark. A mill is not doing good work when it allows any large particles 
of bark to pass through without being crushed. 
The ground Adelaide bark used for the experiments described in this paper 
may be cited as a good example of how bark should be prepared for the 
extraction vats. 
3. The additional cost of grinding, the mechanical agitators required, and 
the resulting cloudy liquors, are factors which adversely affect the use of bark 
in, the powdered state. 
4, For all practical purposes the maximum for a “one liquor period ” when 
water is added to the wattle bark is not above twenty-four hours, and this 
~ period decreases as the temperature increases. 
5. An open diffusion and continuous process, worked on the press leach system, 
appears to be the most useful for the extraction of tannin from wattle bark. 
6. Eight vats are recommended for a press leach system battery working 
under normal conditions; but when the bark swells to such an extent that 
percolation is retarded, then nine vats are recommended, By this means the 
tanner can shift the bark once during the process of extraction. 
7. The amount of tannin destroyed, or the difference between the total tannin 
and the sum of the tannins in solution and in the spent bark, is apparently low 
for wattle bark. (Compare experimental results by Yocum and Faust.) 
8. If the percentage of tannin extracted from a bark were a constant quantity,” 
then the tannin concentration of the liquor drawn off each day would he inversely 
proportional to its volume, but one would expect that the percentage of tannin 
extracted from a bark would decrease as the volume of liquor drawn off each 
day decreased. Within the limits of the experimental work described here, it 
is considered that the minimum volume of liquor to be drawn off cach day 
should be approximately equal to the amount of weak liquor that could be 
drawn off the bark in one pit. 
9. The maximum volume of liquor that can be drawn off the bark each day 
will depend on the strength, or tannin concentration, of the strongest liquor 
required in the tannery. 
10. High temperatures (80° C. to 100° G., or 176° F. to 212° F.) are 
necessary before it is possible to extract a high percentage of tannin from wattle 
bark. 
11. Many tanners fail to get good results because they do not pass sufficient 
water at a high temperature through the bark, 
12. Under the conditions described for these experiments, at least three vats 
must be raised to the high temperatures before suflicient hot liquor will pass 
through the bark to remove a’ good percentage of the tannin. 
13. As the volume of liquor drawn off each day increases, the number of 
vats to be maintained at a high temperature decreases. 
14. From an economic stand-point, the best extraction results will be obtained 
when the process is worked on a large scale, and one good extraction plant in 
the various Australian tanning centres could be expected to supply tannin in 
solution at a much cheaper rate than when each tanner treats his own. bark. 
In submitting the above results, the Committee feel justified in recommending 
the extraction process of the press leach system for wattle bark to the favorable 
consideration of those interested in the tanning industry, as it is considered 
' that this process would be found more advantageous and efficacious than the 
methods generally employed in-Australian tanneries. 
The experiments of the Committee, as described above, were carried out almost 
wholly by Mr. W. McGlynn, chemist to the Committee at the Sydney Technical 
College anning School, under the continual and direct supervision of Mr. F, A. 
Coombs. While the Committee has had a large number of meetings during the 
currency of the work, the Committee considers it only right to draw attention 
to the fact that the chief burden of the work has fallen on Mr. Coombs and 
~ Mr. McGlynn. : 
C.4094.—4 —~ 161 
