A. Hatzfeld

“ Dissolved in tannic acid to the condition of a soluble salt, in proportions which vary according to the degree of hardness to be given to the wood, it is rapidly transformed under the influence of air, and is deposited in the cells of the wood in a solid state, which it petrifies, so to speak, thus increasing the preservative effects of the tannic acid. ”

“ But it is not enough to protect soft wood from rotting; it must also be hardened; and though by the action of tannic acid we in some measure attain this end, the soft materials in the sap-vessels being transformed, still it is important that we should give to woods that are naturally soft a higher degree of hardness, in order to fit them for industrial uses. ”

“ A certain number of observed facts seem to demonstrate that the action of tannin upon vegetable tissues must be analogous to that which is exercised upon animal tissues—operating in the vegetable tissues a kind of tanning, which will have for result the formation of hard and imputrescible albuminous tannates, quite analogous to the gelatinous tannate products in the tanning of skins. ”

“ As to the salts of iron, they are so low in price that it is hardly worth while to estimate their cost. The salts of the protoxide of iron, soluble in tannic acid, carbonate, sulphate, protochloride, and pyrolignite, are easily procured or prepared. ”

“ We may operate by injecting successively tannic acid, and then a soluble salt of iron; or, by means of a single operation, inject, sheltered from the air, the tannate of protoxide of iron, prepared in advance.
Results of experiments demonstrate the efficacy of this system. In fact, we frequently find in ferruginous soils very old oaks of a black color, and in a state of perfect preservation. ”