Bresser junior Biotar Serie Instrucciones De Uso página 14

ing behind you. Adjust the light so that the matt
screen is lit up brightly.
You can adjust the focus of the prepared slide im-
age using the focus knob (2). Make sure to swivel
the microscope arm (9) back into an upright po-
sition so that you can comfortably observe the
specimen.
In a dark room, it is also possible to project the
microscope picture on a white wall. To do this, re-
move the matt screen. Swivel the tripod so that the
upper edge of the projector is horizontal. Keep in
mind that the image brightness is reduced and the
picture will be darker if the projector is far away
from the wall.
14
Experiments
Now that you're familiar with your microscope's
functions and how to prepare slides, you can com-
plete the following experiments and observe the
results under your microscope.
Newspaper print
Objects:
1. A small piece of paper from a newspaper with
parts of a picture and some letters
2. A similar piece of paper from an illustrated
magazine:
Use your microscope at the lowest magnifica-
tion and make a slide preparation from each
object. Place the slide with the newspaper on
the microscope table and observe the slide. The
letters in the newspaper appear broken because
the newspaper is printed on raw, inferior paper.
Now observe the slide with the magazine prepa-
ration. Letters of the magazine appear smoother
and more complete. The picture from the newspa-
per consists of many small points, which appear
somewhat dirty. The pixels (raster points) of the
magazine image appear sharper.
Textile fibres
Objects and accessories:
1. Threads of different textiles: Cotton, linen, wool,
silk, Celanese, nylon and
any others you can find.
2. Two needles:
Put each thread on a glass slide and fray each
with the help of the two needles. Put a drop of
water over each thread with the pipette and cover
each with a cover glass. Adjust the microscope
to a low magnification. Cotton fibres are of plant
origin and look, under the microscope, like a flat,
twisted band. The fibres are thicker and rounder
at the edges than in the centre. Cotton fibres con-
sist primarily of long, collapsed tubes. Linen fibres
are also of plant origin; they are round and run in
straight lines. The fibres shine like silk and exhibit
numerous swellings along the shaft of the fibre.
Silk is of animal origin and consists of solid fibres
of smaller diameter than the hollow vegetable fi-
bres. Each silk fibre is smooth and even and has
the appearance of a small glass rod. Wool fibres
are also of animal origin; the surface consists
of overlapping scales, which appear broken and
wavy. If possible, compare wool fibres from differ-
ent weaving mills, and note the differences in the
appearance of the fibres. Experts can determine
the country of origin of wool based on its appear-
ance under a microscope. Celanese is artificially
manufactured by a long chemical process. All Cel-
anese fibres show hard, dark lines on a smooth,
shining surface. The fibres crinkle in the same
way after drying. Observe the similarities and dif-
ferences between the different fibres.