98 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OP AGRICULTURE. 



Range of durability in railroad ties. 





White oak and chestnut oak 



Chestnut 



Black locust 



Cherry, black walnut, locust 7 



Elm 6 to 7 



Red and black oaks 4 to 5 



Ash, beech, maple 4 



Tears. Years. 



8 Redwood 12 



8 Cypress and red cedar 10 



10 Tamarack 7 to 8 



Longleaf piue 6 



Hemlock 4 to 6 



Spruce 5 





ar-i 



Fig. 4. — "Non-porous" woods. A, fir; -B, "hard" pine; G, soft pine; ar, annual 

 ring; o. e., outer edge of ring; i. e., inner edge of ring; s. w., summer wood; 

 sp. iv., spring wood; rd, resin ducts. 



HOW TO DISTINGUISH THE DIFFERENT KINDS OF WOOD. 



The carpenter or other artisan who handles different woods becomes familiar with those he 

 employs frequently, and learns to distinguish them through this familiarity, without usually being 

 able to state the points of distinction. If a wood comes before him with which he is not familiar, 

 he has, of course, no means of determining what it is, and it is possible to select pieces even of 

 those with which he is well acquainted, different in appearance from the general run, that will 

 make him doubtful as to their identification. Furthermore, he may distinguish between hard and 

 soft pines, between oak and ash, or between maple and birch, which are characteristically different; 

 but when it comes to distinguishing between the several species of pine or oak or ash or birch, 

 the absence of readily recognizable characters is such that but few practitioners can be relied upon 



to do it. Hence, in the market we 

 A- .- ^- B- r > find many species mixed and sold 



indiscriminately. 



To identify the different woods it 

 is necessary to have a knowledge of 

 the definite, invariable differences in 

 their structure, besides that of the 

 often variable differences in their ap- 

 pearance. These structural differ- 

 ences may either be readily visible to 

 the naked eye or with a magnifier, 

 or they may require a microscopical 

 examination. In some cases such an examination can not be dispensed with, if we would make 

 absolutely sure. There are instances, as in the pines, where even our knowledge of the minute 

 anatomical structure is not yet sufficient to make a sure identification. 



In the following key an attempt has been made — the first, so far as we know, in English 

 literature — to give a synoptical view of the distinctive features of the commoner woods of the 

 United States which are found in the markets or are used in the arts. It will be observed that 

 the distinction has been carried in most instances no further than to genera or classes of woods, 

 since the distinction of species can hardly be accomplished without elaborate microscopic study, 

 and also that, as far as possible, reliance has been placed only on such characteristics as can be 

 distinguished with the naked eye or a simple magnifying glass, in order to make the key useful 

 to the largest number. Recourse has also been taken for the same reason to the less reliable and 

 more variable general external appearance, color, taste, smell, weight, etc. 



The user of the key must, however, realize that external appearance, such, for example, as 

 color, is not only very variable but also very difficult to describe, individual observers differing 

 especially in seeing and describing shades of color. The same is true of statements of size, when 

 relative, and not accurately measured, while weight and hardness can perhaps be more readily 

 approximated. Whether any feature is distinctly or only indistinctly seen will also depend some- 

 what on individual eyesight, opinion, or practice. In some cases the resemblance of different 

 species is so close that only one other expedient will make distinction possible, namely, a knowl- 

 edge of the region from which the wood has come. We know, for instance, that no longleaf pine 

 grows in Arkansas, and that no white pine can come from Alabama, and we can separate the 

 white cedar, giant arbor vitae of the West and the arbor vitiie of the Northeast only by the 

 difference of the locality from which the specimen comes. With all these limitations properly 



