16 WLP BORN MAND TS. Es OVWAE IN 
increase is far too small to account for the large changes in velocity 
observed.® It might therefore seem safe to conclude that the presence 
of moisture decreases the value of Young’s modulus. It is, however, 
conceivable that the presence of a small amount of water might exert 
a loading effect upon the vibrations of the bar and consequently re- 
duce the velocity to a much greater extent than would be anticipated. 
In order to show that water actually changes the value of Young’s 
modulus by an amount approximately sufficient to account for the 
observed change in velocity, it was necessary to resort to a static 
method of measuring the change in Young’s modulus. This was done 
in the following fashion. The bar was supported at either end and 
loaded at its center point. A fiducial point at the center of the bar 
was observed with the aid of a micrometer microscope in order that 
the deflection of the center under various loads could be determined. 
This deflection, to a first approximation, is given by the relation 
D=K/E 
where D is the deflection 
E is Young’s modulus 
and K is a constant involving the distance between the sup- 
ports and the dimensions of the bar. 
The data so obtained were found to be in accord with the sup- 
position that water changes the value of Young’s modulus rather 
075 ~ 
YOUNG'S MODULUS - DYNES/CM? 
o 
8 
fo) 
vu 
uo 

fe} 
2 3 4 Ss 6 
WATER ADDED IN PER CENT BY WEIGHT 
Fic. 6.—Variation in Young’s modulus of Amherst sandstone as 
water content is changed. 
§ The increase in density of the bar produced by the maximum amount of water 
added was a trifle more than 6 per cent. The maximum decrease in velocity which may 
be attributed to the change in density is therefore about 3 per cent, whereas changes 
as great as 42 per cent were observed. In this connection it is of interest to note that the 
changes in velocity corresponding to that portion of the curve of Figure 5 lying between 
pone 3 and 5 are sufficiently small so that they may be attributed to the change in 
ensity, 
676 
