SCIENCE AND INDUSTRY. 
SS 
Certain tanners pump liquors from the tan-yard back on to the bark. If 
the used colouring liquors are too’ strong to be pumped away, and must go 
back to the battery, then they should go into the vat which contains liquor about 
equal to. their own density. This practice of pumping these liquors back on to 
the bark is a bad one, and contributes in no small degree to the bad odour 
noticeable at times with some leathers. It makes the extraction process more 
difficult by bringing foul matter into the battery, its economic value has yet 
to be proved even when tanners are colouring in strong liquors, and if the 
bark is properly spent by using the required amount of water the liquor drawn 
off each day must increase in volume and decrease as regards its tannin concen- 
tration. So that pumping back weak liquors may mean that the tanner will 
only get a weak liquor off the head of the battery. The weak liquor cannot 
replace water and give good results. é 
For these experiments the working operations are all completed within that 
period, 7.39 a.m. to 5 p.m., which might be called the working hours per day. 
This requires no further explanation than the statement that a process which 
required attention night and day would not be acceptable to 90 per cent. of 
the Australian tanners. A weak factor in these experimental processes is shown 
when the temperature of the liquors is allowed to fall during the night. The 
results obtained when the temperature of the tail-end vats is at 95° C. show 
that this procedure cannot be responsible for any great loss of wattle tannins. 
This to a certain extent is confirmed by the last two experiments, where the 
one at a maximum temperature of 40° C. during the working day, and the other 
at 35° during the working day and night, give approximately the same results. 
The difference of temperature would mean about 1 per cent. of tannin to be 
added to the latter. 
The decrease in temperature during the night would certainly mean a greater 
quantity of coal used per ton of bark when compared with a process working 
on a large scale as ‘described below. 
The extraction of tannin from bark must be carried out on a large scale to 
get the best results. The greater number of Australian tanners do not* use 
sufficient bark per week to reach this desirable Standard, but the difficulty might 
be overcome by erecting an extraction plant capable of treating all the bark 
required by the tanners in any district. 
This extraction process would be working night and day, and it would then 
be on a basis suitable for the manufacture of extract. The temperature of the 
vats at the head of the battery should not be higher than 40° C., as above this 
temperature the tannins change to a deeper red colour. With the front vats 
at 40° C. and the others at higher temperatures, two. to three vats could be 
emptied and refilled per day, and the time for the bark in a six-vat battery 
would be two to three days. The tail-end vats could be kept at any suitable 
temperatures from 80° to 95° C. 
The temperature of the first three vats at the head of the battery should not 
go beyond 40° C., because it would take quite three vats to remove the greater 
proportion of the light-coloured tannins. The temperature of the fourth vat 
would vary according to the temperature of the liquor pressed forward from 
the fifth vat, which would be about 80° G. in the overflow pipe, and it would 
decrease as it passed through the bark. The fifth, sixth, and seventh vats would 
be at a temperature of 80° to 95° C., and if extraction were complete with 
Seven vats the eighth could be used to heat and remove impurities from the 
water. ; 
The bark will never be completely exhausted as regards tannin, and if water 
has to be used in the extraction processes containing impurities, such as iron, 
salts, &c., which adversely affect the tannin, it will be desirable to first pass 
such water through these spent barks, when one could expect a considerable. 
amount of the impurities to be removed. 
. 
SUMMary. 
1, Spent wattle barks, taken from various tanneries in New South Wales, 
contain considerable amounts of tannin, and these undesirable results can be 
attributed to the faulty methods adopted for the extraction of tannins, 
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