48 



sapTvood were suspended in a saturated atmosphere for three months. To prevent ftingonsgro-wth 

 a little carbolic acid was added to the water and the vessel hermetically closed and placed in a 

 dark room wlicre a very uniform temperature ])revails. At the end of three months the shavings 

 were taken out, weighed at once, and then left to dry. After a few days they were placed in a 

 kiln and dried at 100° C, and it was tV)nnd that for each 10(» cm' of dry wood substance there 

 had been absorbed in — 



P. palustris -W cubic centiuictcrs of water. 



P. 8trol)iis 4,5 cubic centimeters of water. 



which represents tlie water capacity of the sii])woo(l of these two species. 



The following ligures illustrate the daily changes of humidity in shavings of sapwood: 



The weather was clear, and the temperature of the atmosphere rose each day to about 28° C. 



(80° to 85° F.). The shavings were on a plate and in a clean, well- ventilated room. 



July 11, 7 ,a. m 



1 p. in 



4:30 p. m. (temperature 84° ¥.) 



9 p. m 



.July 12. 8 a, m. (warm night) 



10 a, m, (94° F.) 



1 :25 p, m 



3:25 p.m 



8 p. m 



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 usu:tl manner. 



The formulae employed are : 



/i\ -rw -i. e 4^^^^, ^ „,i Weight of fresh wood. 



(1) Density of fresh wood==^^-=^5 — ^ .^ 



^ V oluine ot fresh wood. 



/o\ Tw -w ^ 1 J Weight of dry wood. 



(2) Density of dry wood==f^^i-5 n-,-^^^ -•, 



^ ' V olume of dry wood. 



(3) Shrinkage= ^^^"'^ volume-dry volume. 



(4) Moisture in wood: 



Fresh volume. 



_ Fresh weight — dry weight. 



Fresh weight. 



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

 the weight of 100 cm.' of wood; thus the shrinkage and the amount of moistiu-e become the 

 shrinkage and moisture per cent. 



SHRINKAGE EXPEEIMENTS. 



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

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

 specimens ^ere weighed and measured at variable intervals until perfectly <lry. Some dry pieces 

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

 describing more in detail the.se tests and tlieir resnlts, it may be mentioned that in the immersed 

 l)ieces studied the final 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 1.5 cm. long 

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



To determine the skrinkage in different directiims a iinmber of measurements were made in 

 pieces of various sizes and shapes. In mo.st cases pins were driven into the wood to furnish n firm 

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

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



Since the shrinkage of the entire piece is a result ;int change of form and dimensions of the 

 iadividual cells, :i study of the behavior of the cell elements tliemsehcs during slirinkage wa.s 

 undertaken. Portions of thin sections of the wood of J'. tStrohu.t and 1\ pohistri.s were magnified 



