SHRINKAGE AND STRENGTH OF WOOD. 77 



As in other pines, there is usually an increase of weight in the crown, apparently due to an 

 influence of the limbs, but as this influence is local, so the apparent result is local, and the weight 

 is very irregular for the crown part of the stem ; the pronounced increase is apparent only in the 

 immediate vicinity of the limbs. The absence of a pronounced or sharply defined summer wood 

 makes it difficult and impracticable to apply the microscopic methods to determine the variation 

 of weight from pith to bark on any cross section. From the actual determinations of weight, it 

 appears that for the lower portions of any normally grown tree there is usually at first an increase 

 of weight from the pith outward, reaching a maximum somewhere between the fiftieth and eightieth 

 ring, maintained for a long period and usually followed by a very slow decrease in weight from 

 there on outward. This variation is generally small, and never reaches the proportions met in 

 sections of hard pine, such as Longleaf Pine, where it commonly amounts to 75 to 100 per cent of 

 the weight of the lightest portion. 



Usually about half the weight of a green log is water. The amount of moisture generally 

 varies in the sapwood from about 120 to 160 per cent and from 40 to 60 per cent in the heartwood, 

 the amount for the entire log, therefore, varying with the proportion of sap and heart is greatest 

 in saplings and least in large mature trees, in the latter from about 90 to 120 per cent of the 

 weight of the timber after it is kiln-dried. Tbe wood parts with its moisture as easily as any 

 wood in the market, dries rapidly, with little injury, and may safely be kiln-dried fresh from the 

 saw, though in actual practice this method is almost unknown in the White Pine regions, the 

 usual way of drying by carefully piling in immense piles, being the universal way of seasoning. 

 Well air dried White Pine, as in an ordinary room, still retains 8 to 9 per cent moisture, and if 

 unprotected by oil, paint, etc., is quite susceptible to changes of humidity, absorbing and giving 

 off moisture at every change of temperature and humidity of the air. 



SHRINKAGE. 



In keeping with its smaller specific weight, the shrinkage of White Pine is less than that of 

 other pines. It is greater for sap than heart, and therefore greater for sapling timber than for 

 older trees. From the table on page 71 it appears that the shrinkage in volume varies for the 

 several groups of trees from 8 to 9 per cent, and, like the weight, is quite uniform for the different 

 individuals of each group. 



The ease and rapidity with which White Pine seasons, and the manner of distribution of 

 White Pine lumber, encouraging proper seasoning before use, have done much to earn for White 

 Pine the fame of being one of the woods which do "not shrink" nor "work," a virtue which is not 

 only in part due to the small weight and consequent sniall shrinkage, but is largely the result of 

 proper handling. 



STRENGTH. 



Being the lightest, White Pine is also the weakest among the pines of the Eastern United 

 States, as appears from the following general average: 



Strength of White Pine at 13 per cent moisture. 



Pounds per 

 square inch. 



Compression endwise and in bending to true elastic limit 5,200 



Bending to rnptnre 7, 900 



Modulus of elasticity 1,410,000 



Compression across the grain (3 per cent deformation) 720 



Shearing parallel to fiber 380 



Out of about seven hundred tests made by the Division of Forestry, about 55 per cent fall 

 within 10 per cent of this general average, and 90 per cent within 25 per cent of the same. Though 

 the test series for White Pine was by no means as full as is desirable, the above average results 

 will probably be found fairly accurate and sufficient for general purposes. The table on the next 

 page presents the average results for the several trees. 



