SHRINKAGE AND STRENGTH OK WOOD. 77 



As in other i)ine.s, tliere is usually ;iti iucrease of weight iii the crown, apparently <lue to an 

 intiueni-e of the limbs, but us this iiilluence is local, so the ajiparent result is local, and the weight 

 is very irregular for the crown jiart 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 ditlicult and impracticable to apply the niicroscoi>ic methods to determine the variation 

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

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

 of weight from the pith outward, reaching a maximum somewhere l)etween the fiftieth and eightieth 

 ring, maintained for a long period and usually followed by a very shjw 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 Pioe, where it commonly amounts to 75 to 100 per cent of 

 the weight of the lightest portion. 



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

 varies in the sapwood from about IL'O to IGO per cent and from 40 to 00 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 00 to 120 per cent of the 

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

 wood in the market, dries rapidly, with little injury, and may safely be kilu-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 iu an ordinary room, still retains S 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 74 it appears that the shrinkage iu volume varies for the 

 several groups of trees from S to 9 ])er cent, and, like the weight, is quite uniform for the difterent 

 individuals of each group. 



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

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

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

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

 proper handling. 



STRENGTH. 



Being the lightest. White Pine is also the weakest among the jjines of the Eastern United 

 States, as appears from the following general average: 



Slrenijtlt nf While I'ine at IJ pir cent moisture. 



Pounds per 

 sfjuart- inch. 



Comin-cssion ciulwise :ui(l in liemliiig to true elastic limit 5, 200 



ISeudiu^' to nipt lire V, 900 



Jlotliilns of elasticity 1. 110, 000 



Comiiressiiiu across the grain i 3 per cent deformation) 720 



.shearing parallel to liber 3S0 



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 x)er cent within L'5 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 sutticient for general purposes. The table on the next 

 page presents the average results for the several trees. 



