114 PKOCEEDINGS OF SECTION B. 



water at 45" to. 60° 0. appears to be rather severe when it is compared 

 with the practical requirements of sole leather. As a hide becomes 

 nearly saturated with fixed tannin, it will only combine with more 

 tannin when placed in a stronger solution. This action would be 

 slightly reversible in water at the above temperature, and amounts of 

 fixed tannin would be removed varying with the different tannin 

 materials used in the production of leather. 



The combined tannins is the difference between the total weight 

 of the leather and the sum of the moisture, fats, water solubles, hide 

 substance, and insoluble ash. Any insoluble organic substance con- 

 taining no nitrogen, which can be placed in the hide and is destroyed 

 when estimating the total ash, would be returned as combined tannins. 



Ellagic acid, or tanners' bloom, a decomposition product of ellaga- 

 tannin, is an indispensable constituent of the best sole leather. The 

 tannin decomposes, and the insoluble bloom is deposited on the fibres 

 of the leather, greatly improving the resistance offered to the penetration 

 of water, and increasing the solidity as shown in the best English sole 

 leathers. If organic precipitates or insolubles are returned as combined 

 tannin, and, in the case of bloom, have a beneficial effect on the quality 

 of the leather, the tanner is quite justified in experimenting with both 

 organic and inorganic substances to obtain, by cheaper and quicker 

 methods, the improved qualities of a heavily-bloomed leather. 



Excess of, say, barium sulphate precipitated on the fibres would 

 make the leather hard and brittle, but a small amount might improve 

 the quality ; only physical tests of the leather could explain these 

 matters. 



The degree of tannage is a percentage which represents the 

 proportion of fixed tannin, bloom, &c., to hide substance. At the 

 present time we have no figures to show just how the degree of tannage 

 is related to the wearing qualities of the various leathers. Tanners and 

 boot manufacturers are not familiar with the " Degree of Tannage." 



A more valuable qualitative test is the amount of water-soluble 

 matter. Leather can be divided broadly into two groups — substances 

 removed by exposure to water, and the insoluble residue. If the 

 insoluble residue wears well on the sole of a boot or stands the heavy 

 strain required from some harness leathers, it will not matter what are 

 the constituents of the leathers that answer the final physical tests. 



The tanning industry is surrounded by factors such as hides, 

 bark, temperature, and labour conditions, which are only constant 

 under local conditions. Australian tanners are slowly producing a 

 leather to suit local climatic conditions, and it is to be hoped that this 

 leather will be judged more on its physical properties than on the 

 results obtained by analysis. The latter bear to a certain extent 

 indirectly on the wearing qualities, but the physical is of more import- 

 ance than the chemical side. 



