210
Study of Extension in Wool Fibre
Working
When the apparatus is in use, it operates as shown in Plate III. The fibre to be tested is mounted
on paper mounts, the ends of the fibre being secured with sealing wax at a distance of one inch apart.
This length is selected as a standard for comparative study. The paper is then fixed in the hooks
provided in the apparatus. Along with the fibre, the rider is also put in the hole of the support.
After fixing the upper fixed point of the apparatus, the initial reading at which the pointed end of
the index stands is taken. Readings are taken upto two decimal places, the second place being
estimated by judgment. Water is then allowed to flow out of the tester as a result of which pressure
is exerted on the fibre and it extends. On account of the extension, the tube moves down, and with
it the index also glides downwards along the scale. A careful watch is kept on the movement of the
index. Just when the fibre breaks, reading at the scale is noted. The difference between the initial
and the final readings on the scale gives the limit up to which the fibre extended per unit inch. The
water taken out for breaking the fibre is measured in c.c. and the breaking load is calculated by the
formula:
F = Vr 2 /2
R—r 2
where F is the breaking load,
V, the volume of water drawn,
r, the radius of the float,
R, the radius of the outer cylinder
As soon as the fibre breaks, the float suddenly falls down, with the result that the rider strikes
against the edge of the outer cylinder and thus easily comes out of the hole in the support and
remains suspended on the edge for use again.
To ensure efficient working of this subsidiary device, a ring is fixed at the top edge of the outer
tube just above the scale, through which the longer arm of the rider is made to pass, (Plate III).
This ring serves the purpose of keeping the rider in one plane and does not allow it to go astray
due to the free motion of the inner float, thus ultimately helping the index to glide smoothly along
the scale. Care is necessary to see that the index does not touch the scale, otherwise the resulting
friction will interfere with the movement of the index. Some distance should be left between the
scale and the index. This can be done conveniently by adjusting the upper hook of the tester so
as to suit the requirement before starting the experiment. Once the distance is adjusted, it will
continue to work satisfactorily.
This device is claimed to be particularly suitable as it determines the breaking load and extension
of the fibre at one and the same time. Gohachi Osumi and Etsuro Kato [1937] in developing
their own tester, assert that a perfect tester intended to record the elongation of the fibre must be
simple both in making and handling, and it must measure the elongation on a magnified scale. The
method now described is not only simple, but also denotes the elongation on a magnified scale as the
fibre length is taken as one inch standard and the scale being in one tenths of an inch, enables the
worker to note down even a slight extension with the naked eye.
Preliminary trials
In order to test the accuracy and consistency of the results obtained by this method, preliminary
trials were carried out only on true wool fibres (fine fibres) which are considered to be fairly uniform
with regard to their structure and other characteristics such as length, circumference, strength, etc.
in a particular wool sample. The trials were divided under two heads:
(a) Trials by one observer. Two samples from the shoulder region from ewe no. 477R (sample
No. 1) and ewe no. 663 (sample No. 2) consisting of only wool fibres (other fibres having been removed
from the samples by mechanical means and the classification confirmed by the Benzene test) were
taken. The samples were freed from impurities by a bath in warm benzene. Sample No. 1 was
then divided into several lots and from each lot a small sheaf of fibres was drawn and pooled together
to form a composite sample. This was further treated in a similar way and the process repeated
till a small representative sample was obtained. From this sample, six sets of ten fibres each were