USE OF THE WOOD. 



21 



sizes, these regained more than half the water and underwent over half the total swelling during 

 the first ten days after leaving the kiln (see fig. 4). Even in this less than air-dry wood the 

 changes in weight far excel the changes in volume (sum of radial and tangential swelling), and, 

 therefore, the specific gravity even at this low per cent of moisture was decreased by drying and 

 increased by subsequent absorption of moisture. Immersion and, still more readily, boiling cause 

 the wood to return to its original size, but temperatures even above the boiling point do not 

 prevent the wood from " working," or shrinking and swelling. 



In fig. 4 are represented the results of experiments on the -rate of loss of water in the dry 

 kiln and the reabsorption of water in the air. The wood used was of Loblolly and Shortleaf Pine 

 kept on a shelf in an ordinary room before and after kiln drying. The measurements were made 

 with caliper. 



EFFECT OF "BOXING," OR "BLEEDING." 



"Bleeding" pine trees for their resin, to which chiefly Lougleaf and Cuban Pine are subjected, 

 has generally been regarded as injurious to the timber. Both durability and strength, it was 

 claimed, were impaired by this process, and in the specifications of many architects and large con- 

 sumers, such as railway companies, "bled" timber was excluded. Since the utilization of resin is 

 one of the leading industries of the South, and since the process affects several millions of dollars' 

 worth of timber every year, a special investigation involving mechanical tests, physical and chem- 

 ical analyses of the wood of bled and unbled trees from the same locality were carried out by this 

 division. The results prove conclusively (1) that bled timber is as strong as uubled if of the same 

 weight; (2) that the weight and shrinkage of the wood is not affected by bleeding; (3) that bled 

 trees contain practically neither more nor less resin than unbled trees, the loss of resin referring 

 only to the sapwood, and therefore the durability is not affected by the bleeding process. 



The following table shows the remarkable numerical si milarity between the average results 

 for three groups of trees, the higher values of the bled material being readily explained by the 

 difference in weight: 



The amount of resin in the wood varies greatly, and trees growing side by side differ within 

 very wide limits. Sapwood contains but little resin (1 to 4 per cent), even in those trees in which 

 the heartwood contains abundance. In the heartwood the resin forms from 5 to 24 per cent of the 

 dry weight (of which about one-sixth is turpentine), and can not be removed by bleeding, so that 

 its quantity remains unaffected by the process. 



Bled timber, then, is as useful for all purposes as unbled. 



USE OF THE WOOD. 



In its use the wood of all four species is much alike. The coarse grained, heavy, resinous 

 forms are especially suited for timbers and dimension stuff; while the fine grained wood, whatever 

 species it may belong to, is used for a great variety of purposes. 



At present distinction is but rarely made in the species and in their use; all four species are 

 used much alike, although differentiation is very desirable on account of the difference in quality. 

 Formerly these pines, except for local use, were mostly cut or hewn into timbers, but especially 

 since the use of dry kilns has become general and the simple oil finish has displaced the unsightly 

 painting and "graining" of wood, Southern pine is cut into every form and grade of lumber. 

 Nevertheless, a large proportion of the total cut is still being sawed to order in sizes above 6 

 by 6 inches and lengths above 20 feet for timbers, for which the Longleaf and Cuban Pine furnish 

 ideal material. The resinous condition of these two pines make them also desirable for railway 

 tics of lasting quality. 



