JOMAL OF AGEICETIAL RESEARCH 



DEPARTMENT OF AGRICULTURE 



Vol. IV 



Washington, D. C, August i6, 191 5 



No. 5 



TENSILE STRENGTH AND ELASTICITY OF WOOL 



By Robert F. Miller, Assistant in Animal Husbandry, Montana Agricultxiral Experi- 

 ment Station, and William D. Tallman, Professor of Mathematics, Montatia State 

 College of A griculture 



INTRODUCTION 



The study of the tensile strength and elasticity of wool is compara- 

 tively a new line of investigation. McMurtrie,^ of Illinois, in cooperation 

 with the United States Department of Agriculture, tested a great number 

 of fibers, and Prof. J. A. Hill, of the Wyoming Agricultural Experiment 

 Station, Laramie, Wyo., did considerable work along this line. Other 

 than that, so far as the writer knows, there has been no research on this 

 problem in the United States. 



The exact structure of wool is not well understood. It differs from a 

 hair in that the medullary, or central, layer of cells, corresponding to the 

 heart of a tree, is absent in true wool. The coarse wools, however, possess 

 this layer to some extent and, hence, might be termed "hair" in one 

 sense of the word. The line of distinction can not be sharply drawn. 



McMurtrie ^ measured the breaking strain and elasticity of over 35,000 

 fibers, representing nearly i ,000 samples. He tested 30 fibers per sample 

 to secure a fair average test. In another series tested a few years later a 

 small lock was taken from each sample and the fibers were drawn at ran- 

 dom. In this way it was found necessary to test 50 fibers of each sample 

 to obtain a true average. ^ 



Matthews ^ makes the following statement in regard to this point : 



A fair average of breaking strain and elasticity may be obtained for any quality of 

 fibre by testing about 10 separate fibres and taking the mean of the total tests. If the 

 quality of fibres, however, in a sample does not run very uniform it is best to increase 

 the number of tests to 25 or even 50 in order that a satisfactory average may be obtained. 



Prof. Hill and assistants tested in all 59,400 fibers and proved the 

 fallacy of using only 10 to 50 fibers for a true average. He tested 1,000 

 fibers per sample and divided them into groups of 100. Four of the 

 means of the groups of 100 differed from the mean of the 1,000 by more 



* McMurtrie, William. Report upon an Examination of Wools and Other Animal Fibers ... made under 

 the direction of the Commissioner of Agriculture, p. 217. Washington, D. C, 1886. Pub. by the U. S. 

 Dept. Agr. 



2 Id., p. 425. 



' Matthews, J. M. The Textile Fibres ... ed. i, p. 274. New York, 1904. 



Journal of Agricultural Research, 

 Dept. of Agriculture, Washington, D. C. 



(379) 



Vol. IV, No. s 

 Aug. 16, 191S 

 Mont. — 3 



K->1 A.MICAL 



