COMMERCIAL LINT 141 



and, since even the best machinery cannot completely 



equalize the distribution of tufts of varying length in 



the yarn, it will make weaker yarn than a 



similar sample in which the lengths of all hairs 



are the same and equal to the mean length of the irregular 



sample ; the old adage that the strength of the chain is 



that of its weakest link applies very completely to yarn 



strength. 



The discussion of Strength embodies this adage, and 

 also very much more. In the first place we must dis- 

 tinguish between the different kinds of 



f^t^mrtfc " stren g th "' there are primarily, breaking 



strain or hair strength, hand-impact-testing 



or grader's strength, and the strength of the spun yarn. 



Secondarily there is the strength- variation from fibre to 



fibre, which affects all three classes. 



Hair Strength. We have seen good reason for believing 

 that the breaking strain or impact resistance of single 

 fibres is almost entirely dependent on the sectional area 

 of their walls, independently of their diameter. 



Worked out in this way, it is not without interest 

 to note that the tensile strength of a cotton fibre is about 

 double that of wrought iron, so that lint is not quite such 

 a delicate and fragile substance as one is inclined to 

 imagine it. If the wall thickness is the same in two 

 hairs, the hair strength will be proportionate to the 

 diameter of the hair cell; while if the hair cell diameter is 

 the same in both, the hair strength will be proportionate 

 to the thickness of the wall. Our only reservation in 

 this respect is that it is possible for the texture of the 



