20 KOYAL SOCIETY OF CANADA 



absorption was not <o rapid as at other peinods of the year. It was 

 found, nevertheless, that wood is so sensitive to the etïect of moisture 

 that advantage was taken of this property to determine the relative 

 humidity of the atmosphere. 



I might here remark that it is by no means easy to secure complete 

 saturation by submei-sion. Indeed. I have found that specimens of spruce 

 and pine, after having been submerged for several weeks, were saturated 

 to a depth of less than one-eighth of an inch. This is a matter of import- 

 ance in structural work as, if the timber rapidly absorbed moisture, re- 

 peated wettings might diminish the compressive strength to such an 

 extent as to endanger the stability' of a structure. 



Tension Experiments. 



Tensile tests of kiln-dried specimens are of value as standards of 

 refei-ence. but inasmuch as the timber gradually tends to pass into what 

 I have called the normal state, the tests made between these two condi- 

 tions are of no practical value. 



As long as a specimen contained no moisture, it was found that the 

 extension was directly proportional to the load, so that the corresponding 

 co-efficient of elasticity could be readily determined. As soon, however, 

 as the specimen commenced to absorb moisture, there ensued, under the 

 same load, a gradual but continuous increase in the extension, until the 

 normal state was reached. At this point the effect of the hygrométrie 

 condition of the atmosphere was very marked, the total extension in- 

 creasing or diminishing with the slightest increase or diminution in the 

 amount of moisture. As a further check, the amount of moisture 

 absorbed by a specimen similar to the one under stress was carefalh' esti- 

 mated by frequent readings, and the result showed a variation in weight 

 eoiTesponding exactly with the variation in the extension of the test 

 piece. An additional vérification of these results was obtained by care- 

 fully mounting another specimen, without subjecting it to any stress 

 except that due to its own weight, and jnaking the observations with a 

 Martens extensometer. The resulting effects were precisely similar to 

 those obtained in the other experiments. 



A kiln-dried tension specimen of red pine, with a sectional area of 

 •658 square inches, was placed in the testing machine on April 10th. and 

 was subjected to a load which was gradually increased up to 1.000 lbs. 

 The extensometer was then adjusted to a zero reading, and observations 

 of the extension in one hundred thousandths of an inch were made- 

 The rate of extension during the first day was 6 1 hundred thousandths 

 of an inch per hour. On every succeeding day this rate diminished, but 

 irregularly, according to the humidity of the atmosphere, until the test 

 piece had attained its normal .state. At this point the slightest change 

 in the humidity was reflected in a corresponding change in the extension 



