TIMBER PHYSICS TESTING. 



385 



iiiljnstocl to this north and south line, as shown in the figures. Each spare is then branded by deep dirs with three 



25 

 numbers, as, for instance, thus: -, which signilies that this stick was number I, in log 1', of tree L'5. A facsimile of 



the stenciling is recorded in the log hook, and the sticks there numbered to correspond with the numbering on the 

 logs. After sawing, each stick can be iden titled and its exact origin determined. These three n limbers, then, hrcnirie. 

 the ideutitieatiou marks for all specimens cut from this stick, and they accompany the results of tests in all the 

 records. 



The methods of sawing shown in Nos. '2 and t are called "boxing the heart;" that is, all the heart portion is 

 thrown into one small stick, which in practice may be thrown away or put into a lower grade without serious loss. 

 In important bridge, lloor, or root' timbers, the heart should always be either excluded or "boxed" in this way, since 

 its presence leads to (becking and impairs the strength of the stick. 



Alter sawing, the timbers are stored in the laboratory until they are tested. The "green tests" are made 

 usually within two months after sawing, while the "dry tests'' are made at various subsequent times. One end 

 (liO inches) of each small stick is tested green, and the other end reserved and tested after seasoning. The seasoning 

 is hastened in some cases by means of a drying box. The temperature of the intlowing air in this drying box is 

 kept at about 100 1''., with suitable precaution against checking of the wood, and the air is exhausted by means of 

 a fan. The air is, therefore, somewhat rarefied in the box. The temperature is at all times under control. It 

 operates when the fan is running, and this is only during working hours. 



The mechanical and moisture test are then made according to known methods. 



No. 2. No. 3. 



Flo. 103 Method of sawing test logs. 



EXAMINATION INTO THE PHYSICAL PROPERTIES OF TEST MATERIAL. 



The physical examination consists in ascertaining the specific weight of the dried material, 

 and incidentally the progress and amount of shrinkage due to seasoning; the counting and 

 measuring of the annual rings, and noting other microscopic appearances in the growth; the 

 microscopic investigation into the relation of spring and summer wood from ring to ring; the 

 frequency and size of medullary rays; the number of cells and thickness of their walls; and, in 

 short, the consideration of any and all elements which may elucidate the structure and may have 

 influence upon the properties of the test piece. The rate of growth and other biological facts 

 which may lead to the finding of relation between physical appearance, conditions of growth, and 

 mechanical properties are also studied incidentally. 



SHAPING AND MARKING OP THE MATERIAL. 



The object of this work being in part the discovery of the differences that exist in the wood, not 

 only in trees of different species or of the same species from various localities, but even in the wood 

 of the same tree and from the same cross section, a careful marking of each piece is necessary. The 

 disks are split, first into a north and south piece, and each of these into smaller pieces of variable 

 size. In one tree all pieces were made but 3 cm. thick radially, in another 4 cm., in still others b cm., 

 while in some trees, especially wide-ringed oaks, the pieces were left still larger. In the conifers 

 the outer or first piece was made to contain only sapwood. Desirable as it appeared to have each 

 piece contain a certain number of rings, and thus to represent a fixed period of growth, it proved 

 impracticable, at least in the very narrow-ringed disks of the pines, where sometimes the width of 

 a ring is less than 5 mm. (0.2 inch). 

 H. Doc. 181 25 



