TANNINS FROM WATTLE BARK. 
The proportions of non-tannin matters were always greater for the liquors 
at the head of the battery, and they reached a minimum in those tail-end vats 
that were not exposed to a higher temperature than 80° C. Prolonged exposure 
at a temperature of 95° C. is responsible for an excess of the non-tannin extracted 
from the bark. No explanations are required for using a battery worked on the 
press leach system. Reliable authorities have recommended this process, and, 
apparently, practical tanners in various parts of the world are satisfied that 
by gravitation the liquors can be forced around the battery without creating 
channels in the bark. A plan is shown for an eight-vat battery, where the 
bark would not be shifted from the time it first goes into the battery until it 
is removed as spent bark, and also one for a nine-vat battery, which will enable 
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the tanner to shift the bark once during the time it remains in the battery. 
Shifting the bark will prevent any tendency of the swollen: bark to pack so tightly 
that percolation is retarded. t 
The nine-vat battery is arranged to suit those tanners who want to shift 
the bark once during the time it remains in the battery. The centre vat receives 
all the dry bark which remains there for one day. ‘The bark then is shifted 
into one of the outer vats, and the process now becomes the same as used for 
the eight-vat battery. All the strong head liquors are run off the centre vat. 
Each of the eight outer vats is connected with an overflow pipe, which leads into 
the centre vat. This centre vat is always at the head of the battery. All the 
plugs for drains to the well are placed in the overflow pipe. i 
Results seem to show that the higher temperatures (80° to 100° C.) are 
necessary before one can extract a good percentage of the total tannin from 
wattle bark. Davis writes that the best results for leaching are obtained when 
157 
