抄録
The change in length and diameter of cotton cords stretched in water was studied in the present experiment by just the same method as that in the previous one with unloaded cords.(1) The temperature of water ranged 25_??_31°C. From the results we know that: (1) the ratio l-l0/l0, where l and l0 are the lengths of the cord at the commencement and after t hours' immersion in water respectively, varies with t in a similar way irrespective of the tension of yarns (Fig. 1); (2) the relation between (l-l0/l0)24 at t=24 and the mean tension of a yarn, w/3vgr., is as shown in Fig. 2; (3) the final (t=24) change in length, Δl, and that in diameter, Δr, whether positive or negative, are related with each other in accordance with the formula Δl=-BΔr, where B is a constant depending only on the initial length, l0, and the initial diameter, r0, as well as on the number of twists per length of the cord, N, and that of the thread, n. The same formula is valid for the changes which take place, when the cord is loaded in air, or when it is put in water without load. Under the supposition that the length of each yarn which constructs a cord remains unchanged, we have, denoting the ratio of the mean radius of a yarn to the radius of the cord by a,
l2+4π2(N-n)2(ar)2=const. Thence 2l0Δl+4π2(N-n)2a22r0•Δr=0, and B=4π2(N-n)2a2r0/l0.
The values of B calculated by this formula coincide well with those values obtained from the slope of straight lines in Fig. 3 (Tab. 1). (4) The relation between (l-l0/l0)24 and (r-r0/r0)24 is given as (l-l0/l0)24=-.27(r-r0/r0)24 (Fig. 4).
