MANGROVE TANNING. 
Mangrove Tanning. 
(Summary of Report furnished to the Institute of Science and Industry by the Queensland Tanning 
Committee on a Method for obtaining an Improved Colour in Mangrove-tanned Leather.) 
This summary of the report furnished by the Committee is intended 
to present the result of their work in brief. As the report suggested 
further investigation, it was considered preferable to publish an abstract 
rather than the full report. ; 
The material investigated was a mixture of red mangrove 
(B. ruginera Rheedi) and black mangrove (Rhizophora Mucronata). 
The object of the work was to devise a method by which this material 
could be used to produce sole-leather free from the odour and red 
colour usually associated with mangrove tannage. 
Experiments directed towards an actual bleaching of the extract were 
without practical success, and the precipitation method to be described 
was the only procedure that furnished promising results. It was found 
that the precipitation from the extract of sufficient aluminium salts to 
‘remove about 20 per cent. of the tannins present produced an extract that 
furnished a much lighter coloured leather than the untreated solution. 
Extract of specific gravity about 1.05 requires the addition of about 
1 lb. of aluminium sulphate to every 40 gallons, and to cause precipita- 
tion about 1 Ib. of soda ash in the form of strong solution needs to be 
added. This amount of carbonate varies with different samples of © 
bark, and the correct volume can be ascertained by testing a small 
portion of the extract with measured volumes of the carbonate solution, 
after addition of the sulphate. The precipitate, which requires about 
‘twenty-four hours to settle properly, carries out of solution some tan- 
nins and sufficient colour-forming material to considerably modify. the 
appearance of leather subsequently tanned, which is brown in colour 
and lighter in shade than that formed by untreated material. hes 
The treatment described reduces the acidity of the extract, and a 
method is suggested for restoring this to its original value. The sul- 
phuric acid required for this purpose amounts to about one-quarter of 
the weight of soda ash used. A lime-water test was used to control 
the acidity, but it is of doubtful accuracy under the conditions de- 
scribed, and it may be suggested that a better method, probably physico- 
chemical, might be devised. ; 
Concentrated treated extracts were also prepared and tested in par- 
ticular as a substitute for imported extract for “drumming” tained 
hides. It is customary for tanners to give the hides a final treatment 
with fish oil, and sometimes a little concentrated extract is worked into 
the hides at the same time. It is claimed that this treatment improves 
the leather. For this purpose the mangrove extract was found to be 
at least as good as the imported extract. It was suggested that this 
process of adding extract to leather was’ worthy of investigation to 
ascertain to what extent the extract was fixed on the fibres, and not 
merely mechanically worked into the leather. 
Some costs were furnished based on a price of £15 for wattle and 
£7 per ton for mangrove bark, which indicate that a saving of about 
£80 per week would be effected on a weekly output of 500 hides. The 
cost of concentrated extract was estimated at about £19 per ton. 
The Committee finally recommended that a series of large-scale experi- 
ments, using whole hides, should be carried out before establishing the 
process on a commercial basis. 
437. 
