40 

 Relation between the comprenxire strewjth idkI the percentaye of moisture. 



In Fig. 8 are plotted .some very careful te.sts by I'rofes.sor Bauschiuger to show the relation 

 between the percentage of moisture and the crushing strength. 



There is no question but the crushing and the shearing strength are both greatly reduced by 

 moisture. The crushing test also gives a very fair indication of the strength of the timber in all 

 other ways. In this instance four sticks were taken and sections tested flj'st green, or having an 

 average of .37 per cent of inoisture when computed on the wet weight, or 59 per cent of moisture 

 when computed on the dry weight, as is the practice in the tests made by this Department. The 

 sticks were then dried until there was an avei-age of 14.« per cent moisture on the wet weight, or 

 17 per cent of tlie dry weiglit. The remaining portions of the sticks weic further seasoned until 

 there remained but 8.2 per cent moisture computed on the wet weight, or II per cent moisture on 

 the dry weight, and then tested. This is a smaller percentage of moisture than outdoor lumber 

 ever reaches, as the ordinary humidity of the external aii' will usually maintaiii at least 10 per 

 cent of nxjisture in all kinds of timber. 



When these three groups of results are ])lotted, and tlic most probable cnr\e drawn through 

 them, there is seen to be a remarkable increase in the crusliing strengtii wlien the percentage of 

 moisture falls below fifteen or twenty. The variation in strengtii abo\e tliat limit is very small. 

 Professor Bauschinger has published a great many such curves, all showing the same general law. 

 This curve illustrates tlie necessity foi- Hnding the percentage of moisture for every test of strength 

 made. 



Professor Bauschiuger Inis published very few tests showing the relations between the cross- 

 breaking strength and the moisture, but Fig. 9 is a reproduction of such results as he has given. 



When the percentage of moisture sinks as low as 10 there appears a wide variation of strength, 

 not satisfactorily explained. There would seem to l)e a law of dependence, however, but less 

 marked than in the case of comi)ressive strcMigth. 



Relation between xpeeijie f/rorlti/ and moi^sture. 



In Fig. 8 the '• specific-gravity" curve sliows the relation between the s]>ecific gravity and the 

 percentage of moisture. At first the specific gravity diminishes rapidly as tlie percentage of 

 moisture is reduced, but when this has been reduced to 15 ])er cent the specific gravity changes 

 very little for any further reduction in moisture. This shows that the shrinkage is insignificant 

 until the timber becomes nearly dry, when it swells and shrinks almost directly with the 

 percentage of moisture, so that the weight of a unit volume, which is a measure of the specific 

 gravity, remains nearly constant. This curve is also only one of a great many similar ones given 

 by Professor Bauschinger. 



