HARDWOOn RECORD 



23 



not apparently exert any influence upon the lasting qualities of 

 timbers other than to otfset the effects of abrasion, impact and 

 other influences of wear and tear. In these cases it is apparent 

 that specific gravity and hardness are important ; but in discuss- 

 ing durability the chief consideration is the duration of life under 

 ■ordinary conditions of usage. To illustrate the above, hickory and 

 hard maple, two of our hardest and heaviest of woods (specific 

 ^ravitj- Si and 69 respectively), are classed among our perishable 

 woods. The American elm,' our toughest common wood, is also 

 short-lived when brought into contact with the soil or under the 

 presence of usual atmospheric changes. Four of our weakest and 

 softest woods, redwood, northern white cedar, western red cedar 

 and catalpa, may be classed among the most durable. These are 

 also some of our lightest woods, having specific gravities re- 

 spectively of. 21 (Sequoia icitiihingioniana), .32 (Thuja occidentalis), 

 .38 (Thuja plicata) and .42 (Catalpa speciosa). 



The principal internal influences which determine durability, 

 therefore, must be found in the chemical constitution of the wood. 

 In this respect, coloration, particularly of the heartwood, is the 

 best direct outward evidence of the chemical nature of the dura- 

 bility of wood fibers. What, then, determines coloration? This 

 is to be found in the relative amounts of tannin contained in the 

 •wood elements. Besides tannin, the resins, gums and other sim'ilar 

 compounds found in wood are antiseptic in their nature and there- 

 fore have a direct bearing on the durable qualities of the wood 

 in which they are contained. A German investigator, Heinrich 

 Mayr, states that the more intense the color of heartwood the 

 more durable it is. This is easily borne out by mentioning some of 

 our species of deeply colored heartwood, the durable qualities of 

 which are well known — ebony, lignum-vitie, rosewood, catalpa, red 

 ■cedar, the sequoias or redwoods, black locust, Osage orange, yew, 

 etc. As opposed to these, some of our common species with a light- 

 colored heart are among our most perishable woods, namely, horse 

 chestnut, basswood, maple, Cottonwood, tupelo, hickory, spruce, 

 balsam, etc. To be sure, there are exceptions to this general rule, 

 but, as with most rules, they only help to prove it. Tannin is 

 formed by oxidation in the tissues in the zone between the sap- 

 wood and heartwood as the water gradually disappears from the 

 ■cells and oxygen is admitted. The gradual darkening of the heart- 

 wood after being cut and exposed to the atmosphere is a good 

 illustration of the process of oxidation. Color is to a certain 

 degree dependent upon illumination of the foliage of the tree. 

 Hence, color is deepest in the branches near the point of illumina- 

 tion, not'so deep in the bole of the tree and even more pale in the 

 roots. Wood from trees grown in full sunlight is more deeply 

 <'olored than that from those in a dense forest and is therefore 

 likely to be more durable. In this same connection, tropical woods 

 are likely to be more durable than those grown in a more north- 

 erly climate; so that trees from the same species are more durable 

 when grown in the southern than in the northern extremity of its 

 range. Chestnut wood contains from five to ten per cent of tannin. 

 Turpentine, one of the ethereal oils of wood, becomes oxidized 

 into rosin, which adds considerably to the durabilitv'. The added 

 ]ireseuce of gums is a great factor in rendering wood antiseptic 

 against the bacterial and fungous influences of decay. 



Sapwood is obviously less durable than heartwood, both on 

 account of its saturation with moisture and its lack of protective 

 ohpmical constituents such as tannins, resin, gums, etc., which are 

 usually found in heartwood. The writer has seen cypress and 

 tupelo logs unearthed from a vegetative covering in the swamps 

 along the Choctawatchie river in Florida that, with the exception 

 of the sap which had rotted off, were perfectly sound and v'ielded 

 splendid grides of lumber. Larch logs have also been uncovered 

 in northern Idaho, that were lying prostrate along the ground under 

 western red cedar trees that were up to 1.50 years of age. Only 

 the thin sapwood had rotted off, probably before the covering 

 which excluded the 0X3'geu was complete. 



There is no direct interrelation between rapidity of growth and 

 durability except within a species. That is, a rapidly grown piece 

 of oak is not likely to be as durable as one which grew nnicli 



slower, yet species which inherently grow rapidly, such as black 

 locust, catalpa and chestnut, are found to be durable as well as 

 slow-growing trees, such as longleaf pine, cypress, red cedar, etc. 

 What makes one species more durable than another can only be 

 explained by its inherent qualification to have contained within its 

 heartwood those chemical elements which resist the influences of 

 decay. 



The above discussion has been devoted to the question of natural 

 durability. Artificial durability as applied to timbers has been 

 introduced as a result of the growing scarcity and consequent rise 

 in value of our forest products. This is a big subject and although 

 closely allied to the question of durability, the preservation of 

 timbers by artificial means deserves consideration by itself. Suf- 

 fice it to mention the principal means of increasing the natural 

 durability of wood, which are special niethods of seasoning (such 

 as steaming and smoking), charring the surface of wood that is 

 brought into contact with the soil, painting, tarring and the im- 

 pregnation of chemical preservatives into the wood fibers. 



The state forester of Ohio has recently published the result of 

 an exhaustive investigation of the relative durability of several 

 species used for post material, under a wide range of conditions. 

 This list shows the following species, given in order of durability: 

 Osage orange, black locust, red cedar, mulberry, white cedar, 

 catalpa, chestnut, white oak and black ash. 



The following list is offered to show the comparative durability 

 of some of our American timbers by groups. This is not presumed 

 to obtain for all conditions, because it is too well known that there 

 is a considerable lack of uniformity in the durable qualities of 

 woods even within the same species and under similar conditions 

 of placement. 



Verv Dl'r.\bi.e 



IIAltDWOODK, 



Black locusl. 

 Catalpa. 

 JIahogauy. 

 Osage orange. 

 Mulberr.v. 

 Chestnut. 

 Black walnut. 

 Live oak. 

 Sassafras. 



Wliite oak. 

 Post oak. 

 Black a.sh. 

 Ilonc.v locust. 

 Cherry. 

 Persimmon. 

 Red elm. 

 Bur oak. 



Yellow poplar. 

 Red ash. 

 Red oak. 

 Scarlet oak. 

 Butternut. 



Cottonwood. 

 Wliite elm. 

 Rod gum. 

 Hard maple. 

 White ash. 

 Black oak. 

 Red birch, 

 li, eeh. 

 Hickory. 

 Cucumber. 



Black gum. 

 Water gum. 

 Basswood. 

 Buckeye. 

 Sycamore. 

 Grey birch. 

 I'aper birch. 

 .\spen. 

 Will'uv. 



CONIFERS. 



Incense cedar. 



Cypress. 



Western yew. 



Arbor vitae. 



Western red cedar. 



Redwood. 



Southern white cedar. 



Lawson cypress. 



D['K.\ELE 



Longleaf pine. 

 Cuban pine. 

 Eastern larch. 

 Western larch. 

 Dou.^las lir. 



IXTEKMEDIATE 



White piue. 

 Norway pine. 

 Sugar pine. 

 Shortleat pine. 



Perisii.\ble 



Loblolly pine. 

 Red spruce. 

 Hemlock. 



Western hemlock. 

 Sitka spruce. 

 Noble Rr. 



Kn^lemaun spruce. 

 Pitch pini'. 



Veiiv Perishable 



Lddgepole piue. 

 .I:iek pine. 

 White spruce. 

 Ualsara fir. 

 White fir. 



N. C. B. 



