SCIENCE AND INDUSTRY. 
the final liquors are at a temperature of 205° to 212° F. (96° to 100° C.). 
Parker and Proctor show that if the tannin from wattle bark be extracted at 
various temperatures, the best results will be obtained at a temperature of 
80° C. They worked on-an analytical scale, using finely-ground bark and an 
excess of water. The results obtained when all the tannins extracted were 
exposed to a temperature of 80° C. were the highest, and were called the 
maximum yield. So that their maximum yield and the total tannin in the 
bark, as found by the present analytical method for extracting tannin from 
bark, may differ, and probably the latter would be higher. When the results 
obtained by these. workers at. various temperatures were compared with results 
obtained, we notice that more tannin is extracted by Parker and Proctor, 
especially at the lower temperatures. This can be explained by assuming that 
the amount of tannin extracted at any constant temperature will decrease as 
the volume of water used decreases, and as the size of the particles of bark 
increases. ‘The spent bark from the tail-end vats at 40° C. would probably still 
give off an appreciable amount of tannin if more water were used or more 
water and extra vats. The extra water would mean weaker liquors, and if 
the extraction were to reach the 94 per cent. obtained at this temperature by 
the workers mentioned above, it would probably mean accumulation of a great 
volume of weak liquor. To prevent this undesirable result and still obtain a 
greater yield of tannin in solution, one could raise the temperature of the tail-end 
vats to 95° C.,as shown for the fourth experiment, when the yield was 90 per 
cent. of the total tannin. 
The strength of the last liquor off the spent bark will always show if 
extraction is nearly complete for any one temperature. It may be said that if 
the final liquor from the spent bark of any process has a high density value, say 
above 3° barkometer, then the bark requires more water, or more cold or hot 
liquor as obtained by increasing the number of hot or cold vats in the battery. 
The amount of red tannins in a liquor is greater the higher the temperature 
of the liquors during the process of extraction and the greater the percentage 
of tannin extracted from the bark. All wattle barks contain a certain propor- 
tion of red tannins, which are only extracted at the higher temperature. The 
light-coloured tannins change to red when exposed to temperatures above 40° C., 
so that one could say that wattle-bark liquors always contain some red tannins 
that were present naturally in the bark, and other red tannins that owe their 
origin to high temperatures or faulty methods during the process of extraction. 
If the light-coloured tannins be removed at a low temperature the more 
difficulty soluble or red tannins are left in the bark. Some tanners object to 
using the latter because of the reddish colour of the resulting leather. The 
amounts of tannin extracted at the various temperatures shown in these experi- 
ments are results that should show the tanner the value of temperature 
extraction process. The amount of tannin extracted and the colour of the 
leather is.regulated by the temperature of the tail-end yats, and if a tanner 
reduced the temperature to improve the colour of the leather, then he also 
reduces the percentage of tannin extracted from the bark. 
When 90 per cent. of the tannin is extracted with tail-end vats at 95° O. 
the resulting liquors are cloudy and red. These liquors are suitable for the 
average sole and harness leather. For special lines, where colour is an important 
factor, it may be advantageous to lower the temperature of the tail-end vats 
and reduce the amount of red tannin extracted from the bark, but before doing 
this for any leather, a tanner should consider what can be done to improve 
the colour by using a mixed tannage. Good results can be obtained on a slightly 
reddish leather by the careful use of small quantities of titanium salts. 
For the production of strap, bag, kip leathers, &c., it might be necessary to 
reduce the temperature of the tail-end vats to a considerable extent, but not 
lower than 60° OC. The maximum temperature for extraction at a basil tannery 
would probably be below 60° C. A large number of tanners, who produce 
various leathers, only use water at ordinary temperature for the production of 
their liquors. Ordinary temperature in the cold season may be 12° CG. (54° F.). 
Such a temperature is too low to give fair results. So that one could say 
that there is no tanner. in Australasia who does not require to work some of 
his extraction vats above ordinary temperature. : 
These experiments have shown that very strong or highly concentrated liquors 
can be removed daily from the battery when the yolume of liquor drawn off 
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