Apr. 15, 1920 Influence of Humidity upon Wool Fiber 59 



Graphs showing the variation in the tensile strengths of three different 

 samples of wool are shown in figure 3 in the curves A-A, B-B, and D-D. 



The fibers tested in these curves range from 0.008 to 0.038 mm. in diam- 

 eter. The number of fibers tested at each humidity varies considerably. 

 In some cases only 30 or 40 were tested, while in other cases as many as 

 250 of a given diameter were tested. Sample A of curve A-A ranges in 

 fineness from 0.008 to 0.018 mm. The tensile strength decreases from 

 667 to 260 mgm. per thousandth of a square millimeter at the lowest 

 point. Sample B shows a decrease from 466 mgm. at o.oi mm. to 315 

 mgm. at 0.022 mm. The cur\^e of sample B follows that of sample A 

 very closely from a diameter of o.oi mm. to one of 0.018 mm. and rises 

 slightly from a diameter of 0.018 mm. to one of 0.022 mm. Sample D 

 decreases from 320 mgm. at 0.023 rnni- to 232 mgm. at 0.038 mm. 



These curves show that the tensile strength of wool decreases with an 

 increase in diameter. The drop is most abrupt with the sample of fine 

 wool. The coarsest sample has the most gradual drop in its diameter 

 and tensile strength curves. If the breaking strength of wool varied 

 directly as the area of cross section, the curv^e would follow the line E-E. 

 If the breaking strength varied as the diameter or circumference, the ten- 

 sile strength curve would follow the line F-E. The curve for the tensile 

 strength of sample D follows the line D-D and lies between these two 

 lines E-E and F-F. This fact seems to indicate that the breaking 

 strength of medium and coarse wool varies with some power of the diam- 

 eter which lies somewhere between the first and second. 



For fine wool like sample A, a curve showing the strength of the wool 

 very closely follows a curve plotted with i , or any constant, and the first 

 power of the diameter. This fact indicates that the breaking strength 

 of fine wool does not vary directly with the area of the cross section but 

 with a value which is very close to the first power of the diameter. Curve 

 C-C shows the relation between the tensile strengths and diameters of 

 wool fibers obtained from data published by Hill.^ In the present ex- 

 periment, 1 ,000 fibers were broken to obtain the points in this curve, and 

 each diameter was measured after breaking as nearly as possible at the 

 point of breakage. This curve also follows very closely the curve F-F. 

 By inspecting the graphs it is easy to see that the widest variations in the 



curve F-F plotted from j^are found at the smallest diameters. As this 



curve approaches the larger diameters it tends to become rather flat. 



In the first three samples of Table III there is a large variation between 

 the largest and smallest tensile strengths of the wool fibers of those sam- 

 ples. When fibers are tested with such a wide variation in their tensile 

 strength as is found in locks of fine wool, it is necessary that these fibers 

 be carefully mixed in order to get satisfactory results. There is a ten- 

 dency for an operator to pull the largest fibers in fine wool, while with 



' Hill, J. A. studies on the .strength and elasticity op the wool fiber, i. the probable error 

 OP THE MEAN. /jiWyo. Agr. Exp. Sta. 21st Ann. Rpt., 1910-11, suppl., 139 p. 191 1. 



