188 Processes for Wood-preservation. 



thickened and hardened, by deposit of material peculiar to the spe- 

 cies. It is dryer, heavier, and contains less potash than the newer 

 wood. Still, an iron tube driven deeply into the heart of a maple 

 tree will yield sap, showing that there is circulation to some extent 

 still present. In many trees the heart wood may decay without ap- 

 parently lessening the vigor of growth. 



741. Many processes have been devised to increase the durability, 

 not only of the sap wood, but of the whole tree, either by rendering 

 it impervious to moisture, after thorough seasoning, or by neutral- 

 izing the tendencies to decay, or by injecting substances in solution 

 that become unalterable and permanent, either by directly uniting 

 with the tissues of the wood or by forming new combinations be- 

 tween different substances injected into it. 



742. When the pores of wood are filled with other substances of 

 an oily or resinous nature, they show less tendency to warp or split, 

 simply because they do not absorb and give out moisture with the 

 changes of atmosphere. 



743. In some of these processes the attempt is made to render 

 wood harder, stronger, less combustible, more dense, more flexible, 

 or of richer color, or in other ways more valuable, as well as more 

 durable. 



744. Of the two hundred or more antiseptic processes that have 

 been recommended for preventing the decay of wood, we can only 

 notice the more important.' They consist generally in torrefication 

 of the outside, or in the injection or absorption of metallic or non- 

 metallic salts, of acids and their bases, of essential oils, or of resin- 

 ous or oily substances. The chemical action appears to be different, 

 according to the process used, the albumen being coagulated in 

 some, while insoluble and durable mineral and organic combinations 

 are formed in others. Wherever metallic salts are applied in the 

 preservation of wood, they should be neutral, as an excess of acid 

 would act upon the vegetable fiber and destroy it. From the latest 

 results of scientific inquiry, it appears that the real cause of decav 

 is probably due to the action of organized ferments, /wng'i or bacteria, 



1 About 120 American patents are on record and in force at the time of 

 ■writing. Wo can not undertake to enumerate them here; some are not 

 worth notice, and the few that we mention' are placed in their alphabetical 

 order, not because they are better than others, but because they are perhaps 

 better known. 



