382 



Journal of A gricultural Research 



Vol. IV, No. s 



is only i to 1.19. Thus, in comparing the breaking stresses we get a 

 greatly distorted idea of the difference in the strength of the fabric that 

 would be manufactured from the wool. 



A large number of tests were then made to determine the tensile 

 strength of the fibers. The results are given in Table II. 



Table II. — Results of testing fibers of wool for tensile strength — sheep 6jgS; sample from 



hip 



Lot of fibers. 



Coefficient of 

 variation. 



Tensile 

 strength. 



Coefficient of 

 variation. 



First 100. . . 

 Second 100 

 Third 100. . 



Dgm. 

 46. 28 ± I. 53 

 44- 75 ± I- 26 

 51. 73±i. 19 



Per cent. 



3- 31 

 2.82 

 2.30 



Dgm. 

 74.765 ±2,146 



75.293il.573 

 76,973 ±1,452 



Per cent. 

 2.65 

 2. 09 



Fig. I. — Curve showing the regularity of stretch and the abrupt break of 

 merino wool after the elastic limit is passed. X = elastic limit. 



This shows an aver- 

 age coefficient of varia- 

 tion of 2.81 per cent 

 for the stress and 2.21 

 per cent for the tensile 

 strength. 



ELASTIC LIMIT 



However, there are 

 other elements that 

 are even more im- 

 portant than the ten- 

 sile strength. We do 

 not care so much that 

 a fabric shall have a 

 high resistance to a 

 tearing force as that it 

 shall have wearing 

 qualities. If we catch 

 our clothes on a nail 

 and tear them, the 

 force exerted is usually 

 so great that any slight 

 variation in the 

 strength of the cloth 

 will make no differ- 

 ence. Young's modu- 

 lus, which is the stress 



per unit area of cross section divided by the strain per unit length, will 

 show the degree with which a fabric v/ill withstand deformation under 

 ordinary forces. Thus, we expect to find that when the wool has a high 



