26
140½
78
243
200
390
The preceding is a table of the diameters of cotton yarns from 1’s counts to 200’s. The number given as the diameter is the number of threads which occupy the space of one inch when laid as close together as possible without compression.
A perfectly balanced plain cloth will require one-half this number of threads per inch, plus, perhaps, 5 per cent. for the threads being forced somewhat out of the same plane in weaving.
Relative Diameters of Yarns.—The “counts” of yarns indicate the number of hanks in 1 lb., and therefore a given length of 30’s is twice as heavy as the same length of 60’s; but the diameter of the 30’s will not be twice that of the 60’s, as the yarns are cylindrical, and the diameters will vary as the square roots of the areas, which in this case are as 1: 2.
If one thread is four times as heavy as another, and if it is of the same density—which in these calculations is assumed, although it is not strictly correct—the diameters of the two threads will be as 2: 1. For example, looking at the tables, the diameter of a 60’s is seen to be the 1/213 of an inch, whilst the diameter of a thread four times the weight, viz. 15’s, is seen to be 1/106½ of an inch, or exactly twice the diameter of the 60’s thread.