SITRINKAGK AND STUENGTII OI'" WOOD. ( ( 



As ill otliei- jiines, tluMi' is usually an iiicroase of weight in tll(^ <nown, apparently due to an 

 iutlueiK-e of tlie limbs, but as lliis inlluoiicn is local, so the aiiparciit result is loc^al, and tlif, \veij;lit 

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

 iniiiKMliato vicinity of the limbs. The absence of a pronounced or sharjily defined sununcr wfxid 

 makes it dillicult and im|iracticable to api)ly the microscopic methods to determine the vaiiatioii 

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

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

 of weight from the jiith outward, rea<^hiiig 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 comniouly amounts to 75 to 100 jier cent of 

 the weight of the lightest portion. 



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

 varies in the sapwood from about 120 to 1(!0 per cent and from 40 to 60 per cent in the heartwood, 

 the amount for the entire log, therefore, varying with the proi)ortion of sap and heart is greatest 

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

 weight of the timber after it is kiln dried. The wood jiarts 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 practi(;e this method is almost unknown in the White I'ine 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 ((uite su.sceptible 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 ])ines. 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 !• 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 small shrinkage, but is largely the result of 

 proper handling. 



STRENGTH. 



P>eing the lightest. White Pine is also the weakest among the pines of the Masterii rnited 

 States, as apjiears from the following general average: 



Strength of Jl'liitc I'ine at 1.' pir cenl moisture. 



PoinulH i>or 



Hi|U:irc ilicli. 



C'nmprossiDii enilwise and in licndiiii; to tine elastic limit 5, 200 



Hi'niliu;; to inptnre T. 900 



Modulus ol' cla-sticity 1. 110. (H)O 



C'onipiossion across tlic grain (3 1)<t cent di't'ormation) 720 



Shearing parallel to liber ^iJ^" 



Out of about seven hundred tests made by the Division of Forestry, about i^>fi ]»er (■ent fall 

 within 10 per cent of this general average, and 90 jier 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 sufticient for general purposes. The table on the next 

 page presents the average results for the several trees. 



