TIMBER PHYSICS - PHYSICAL EXAMINATION. .'SSI 



does in one of the instruments thus far used. The pan with water is then weighed, the pan itself 

 being tared by a. bag of shot. The water is poured out, the pan wiped dry. and the process begins 

 anew. To work well it takes two persons, one to weigh and record. The water pan is a seamless 

 tin pan, holding about 1,500 ce. of water and weighing only 144 grains. The temperature as well 

 as density of the water arc ascertained, the latter, of course, omitted when distilled water is used. 

 To maintain the water at the same temperature it requires frequent changing. 



DRYING. 



After marking, the pieces are left to dry at ordinary temperature. Then they are placed in a 

 dry kiln and dried at 100 0. 



The drying box used is a double-walled sheet-iron case, lined with asbestus paper, and heated 

 with gasoline. The air enters below and has two outlets on top. The temperature is indicated by 

 a thermometer and maintained fairly constant. 



After being dried, the pieces of wood are weighed and measured, in the same way as described 

 for the fresh wood, and from the data thus gathered the density, shrinkage, and moisture per cent 

 are derived in the usual manner. 



The foriuuliu employed are : 



t of * 81 woo 



(1) Density of fresh - 



Volume of fresh wood. 



,, , TTCIKIII; of dry wood. 



(2) Density ot dry wood= J 



Volume of dry wood. 



(3) 



- 1 



Fresh volume. 



Fresh weight dry weight. 

 (i) Moisture in wood= 



Fresh weight. 



In presenting these values they are always multiplied by 100, so that the density expresses 

 the weight of 100 cm. 3 of wood; thus the shrinkage and the amount of moisture become the 

 shrinkage and moisture per cent. 



SHRINKAGE KXI'KRIMKNTS. 



To discover more fully the relations of weight, humidity, and shrinkage, as well as "checking" 

 or cracking of the wood, a number of separate experiments were made. A number of the fresh 

 specimens were weighed and measured at variable intervals until perfectly dry. Some dry pieces 

 were placed in water and kept immersed until the maximum volume was attained. Without 

 describing more in detail these tests and their results, it may be mentioned that in the immersed 

 pieces studied the tinal maximum volume differed very little, in some cases not at all, from the 

 original volume of the wood when fresh; and also that in a piece of white pine only 15 cm. long 

 and weighing but 97 gs. when dry, it required a week before the swelling ceased. 



To determine the shrinkage in different directions a number of measurements are made in 

 pieces ot various sixes and shapes. In most cases pins were driven into the wood to furnish a firm 

 metal point of contact for the caliper. A number of pieces of oak were cut in various ways to 

 study the effect ot size, form, and relative position of the grain on checking. 



WOOD STRUCTURE. 



The most time-robbing, but also the most fascinating, part of the work consists in the 

 study of the wood as an important tissue of a living organism; a tissue where all favorable and 

 unfavorable changes experienced by the tree during its long lifetime find a permanent record. 



GKNERAL APPEARANCE. 



For this study all the specimens from one tree are brought together and arranged in the same 

 order in which they occurred in the tree. This furnishes a general view of the appearance of the 

 stem; any striking peculiarities, such as great eccentricity of growth, unusual color, abundance 

 of resin in any part of the stein, are seen at a glance and are noted down. 



A table is prepared with separate columns, indicating 



(1) Height of the disk iu the tree (this being furnished by the collector's notes); 



(2) Radius of the section; 



