259 
1906-7.] The Strength of Twisted Threads. 
important factor in determining the strength of a given thread within the 
limits of useful requirements, a point is ultimately reached beyond which 
increased twist makes no material addition to the strength of the thread. 
The point raised by Professors Htibner and Pope, that twist is the controlling 
factor in the strength of a yarn, is not necessarily true under all conditions. 
Indeed, it is only true throughout the length of a fairly uniform thread. 
If we experiment with “ pointed ” or “ t witty ” thread, such as is frequently 
met with in woollen spinning, a very different result will be obtained. 
The thread under test will be found to have broken at the “ twit.” To see 
how this may come about, let us suppose that the 30/30-cut Saxony of 
Table III. had been a “ pointed ” or uneven yarn instead of exceptionally 
uniform as it was, and that one lumpy section contained 150 fibres and had 
six turns per inch, also that a second t witty section contained 100 fibres 
and had fourteen turns per inch. These are average results taken from 
an actual experiment on the distribution of twist. The twitty part is 
probably weaker than the lumpy part in the ratio of 2:3, owing to the 
reduction in fibres ; and from Table III. we see that the increase of strength 
due to greater twist is in the ratio - 92 : P10. 
Therefore, if W is the strength of the lumpy part, the strength of 
the “ twit ” is probably 
o 
= Wx — 
3 
MO 
x 
•92 
= *8W . 
The “ twit ” would thus break with 80 per cent, of the load required to 
break the lumpy part. 
The Manchester investigators inferred that the variation in twist in the 
various threads of their sample yarn was responsible for the variation in 
strength so well recorded in their tests. 
Taking the above example, and even allowing for decrease in the 
number of fibres, which they did not do, the strength of the twit 
would 
[ W *T*T 
= P56W , 
a very improbable result. Still less probable would their own statement 
work out as it stands, that the strength of the twit would 
= W x 
14 
6 
2-33 W 
