230 THE POPULAR SCIENCE MONTHLY. 



into an insoluble salt, of an intense black color. Dissolved in tannic 

 acid to the condition of a soluble salt, in proportions which vary ac- 

 cording to the degree of hardness to be given to the wood, it is rap- 

 idly 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 efiects of the tannic acid. 



Thus we find resolved, in a manner simple and practical, the ques- 

 tion of the introduction of an insoluble salt into wood. "We may oper- 

 ate 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. I will cite an ex- 

 ample that is quite remarkable. 



In 1830 there were found at Rouen pieces of oak-wood, from some 

 piles of a bridge built in the year 1150. This wood resembles ebony, 

 of which it has acquired the hardness and the color. Chemical analy- 

 sis has demonstrated that this modification was owing to the presence 

 of tannate of peroxide of iron (Berthier). Argument and experience, 

 therefore, agree in deciding in favor of the process which I propose. 



The bark of most trees, the young branches and leaves, especially 

 of the oaks, birches, elms, sumacs, chestnuts, and walnuts, the roots 

 of the tormentil, and snake-weed, the green shells of horse-chestnuts, 

 and the extracts of exotic woods, contain a large proportion of tan- 

 nin, to which they owe their astringent properties. 



The First Cost of the Materials used foe In^jection. — In the 

 present state of industry, we can procure tannin at one franc, at most, 

 per kilogramme, in the form of extracts of wood that are employed in 

 dyeing ; but we may remark that these products, employed now only 

 for dyeing and tanning, utilize only a very small quantity of the re- 

 sources of the vegetable kingdom. There is no doubt that a consid- 

 erable consumption of this product would lead to the establishment 

 of numerous factories, principally in the poor regions, where chest- 

 nut and other suitable kinds of trees occur. The industrial wealth of 

 the country would thus be augmented, and, at the same time, the 

 price of this new product would be considerably reduced. Even at 

 the present price, six hundred grammes being sufficient for the injec- 

 tion of one sleeper, the cost of the tannic acid would not exceed -^-^-q 

 of a franc per sleeper. 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. The 

 pyrolignite, which seems the most convenient, is worth twenty francs 

 the hundred kilogrammes, and, at a standard of 20° Baume, contains 

 about seven per cent, of iron. Of this, tannic acid neutralizes twelve 



