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METHODS OF ANALYSIS OF WOOL FIBRE [Vol. XXIV, Part III,
FIBRE DIAMETER OR FINENESS
Fineness is one of the most important attributes of wool fibre and the spinnabili-
ty of wool to fine, medium or coarse counts is mainly influenced by its diameter.
Preparation of the slide. The sample obtained either from a bale or from the
body region of a sheep (as detailed before) is washed free of impurities in benzene
and in one per cent solution of sodium oleate at 40°c. It is finally rinsed in distilled
water and dried over a hot electric plate at low temperature. The sample is then
cut into small pieces of about half millimeter in length over a glass plate with the
help of a pointed pair of scissors.
The pieces are thoroughly mixed with the fine
points of a brush and are arranged on the glass plate into a square of 1 in. X 1 in.
with the help of the sharp edge of a razor blade. The square is divided into 16 zones
of approximately equal sizes, from each of which, a small quantity of fibres is
taken with a mounting needle. These are transferred to a few drops of cedar wood
oil on a slide 3 in. X 1½ in. The fibre pieces are stirred with the cedar wood oil to
get a uniform distribution. A cover glass 2 in. X 1 3 / 8 in. is gently lowered on to the
slide by placing the shorter edge of the cover glass in contact with the slide. A
gentle tap of the mounting needle on the cover glass will give uniform distribution
of the fibre pieces and prevent any air bubble accumulation.
Apparatus. The apparatus which is commonly used for diameter measure-
ments is the one evolved at the Wool Industries Research Association, United
Kingdom, and is called the WIRA Projector. This method has also been approved
by the International Wool Standards Organization. The Zeiss Lenameter and
the Bauch and Lomb Projectors also make use of the same principle as that used
in the WIRA Projector (Plate VI, fig. 1.). A short description of the WIRA
Projector is given below :
' It is a simple instrument to handle and the method of fibre measurement
is based on the projection of the fibre at 500 magnification on to a
screen. The apparatus consists of a lamp house and a stage which
supports the slide for examination. The objective and eyepiece
magnify the fibres. The circular screen on which the image is projected
has a 5 cm. wide transparent ruler graduated in millimeters. The
ruler can be diametrically moved across the screen between the guides.
A circle of 7 cm. in diameter is drawn in the centre of the screen D.
The rotation of the knob E traverses the slide in a direction at right
angles. Rotation of F focusses the image sharply on the screen.'
Procedure
The projector is calibrated before the slide is mounted with a micrometer scale
of a size 1 mm., sub-divided to 0.01 mm. This scale is mounted on the stage and
the magnification is adjusted so that 0.1 mm. of the micrometer scale gives 50 mm.
as measured on the screen.
The slide is mounted on the stage, cover glass downwards and moved to one
extreme corner. The traverse knob is rotated until a fibre image is brought into
the field on the screen and focussed. The screen is rotated until the length of the
ruler is perpendicular to the fibre image. The ruler is moved through the guides
until a centimeter division coincides with one edge of the image and the diameter