1906-7.] 
249 
The Strength of Twisted Threads. 
per unit length, and no formula from which the degree of twist is absent can 
make any pretension to representing the actual conditions which obtain in 
a twisted thread. Probably the most important experimental evidence that 
has ever been published on the strength of threads will be found in a 
paper entitled, “ Influence of Certain Reagents on the Tensile Strength and 
on the Dyeing Properties of Cotton Yarn,” by Professors Julius Hubner 
and William J. Pope, F.R.S., of Manchester, read before the Manchester 
section of the Society of Chemical Industry on January 9, 1903. In each 
of their tests they broke from 100 to 120 threads, each of 10 cm. length, 
on a Schopper testing machine, so as to obtain a mean result with a 
satisfactory degree of accuracy. The Schopper testing machine is a 
product of the Berlin Charlottenburg. It is one of the most elaborate and 
is the most accurate of testing machines at present available for testing 
single threads. Further, the limits of accuracy to which the mean results 
could be relied upon were carefully determined by applying the method of 
least squares to the observations. They were thus enabled not only to 
give the mean tensile strengths for cotton yarn in its natural state and 
after treatment with boiling water, sodium carbonate, sodium hydroxide, 
potassium iodide, and other chemical reagents, but to state that the limits 
of error did not exceed \ per cent. Unfortunately, these gentlemen did 
not confine their conclusions to the problems which they ostensibly set out 
to solve. They committed themselves to the statement “ that for one and 
the same yarn the tensile strength is directly proportional to the twist.” 
They founded this statement on what seems to me to be insufficient 
experimental evidence. 
After making the strength tests referred to above, a series of fifty-eight 
determinations of the twist were made on 10-inch lengths of the same 
two-fold 50’s raw Egyptian cotton yarn as had been used for the strength 
tests. From the results of these determinations it appeared that the twist 
varied from 220 turns to 30*3 turns per inch, the mean being 25 - 66 turns 
per inch. The twist being the main factor in determining the tensile 
strength of a cotton yarn, the paper went on to show that the above three 
twist numbers, viz. 22‘0, 30'3, and 25'66, are in the ratio 324 : 446 : 378, which 
is practically the same as the ratio 330 : 440 : 378, the lowest, highest, and 
mean values of the tensile strength in grams taken from the table of results. 
The conclusion above mentioned was then drawn. That this conclusion 
is not altogether logical in several particulars will be evident if we consider 
the following points 
(1) If it had been possible to ensure that the same number of fibres 
were present in every cross section of the thread, there would not have 
