Introduction: By preparing a slide, you will be able to identify and classify organisms living in soil.
Obtain a glass slide and a cover slip.
Deposit a very small portion of the soil-water mixture onto the center of the slide.
The mixture should only be a drop approximately 10mm in diameter.
Gently cover the solution with the cover slip. Do in such a way that the cover slip falls
from one end to the other (eliminates air bubbles), instead of just dropping it right on
Leave the slide on the table and plug in your microscope.
Flip the switch on the side and turn it on.
Now put on drop of oil on your cover slip.
Place the slide on the stage, and make sure that the metal clips hold the slide securely.
Adjust the lens to 100X, or to "oil immersion."
VERY GENTLY, turn the coarse adjustment knob (the large knob) TOWARDS you until
the lens reaches the oil. The oil should disperse from a bubble shape to a flat shape once
the lens reached it. BE VERY CAREFUL not to grind the lens into the cover slip. The lens
should never touch the cover slip.
Now look through the eye piece and rotate the fine adjustment knob (the smaller knob) until the view becomes clear.
If you have problems with step #10, turn the coarse adjustment knob AWAY from you
and repeat steps #9-10.
Draw a picture of your soil particle and record below:
How to estimate the size of a soil particle: Soil particles are very small. They may be
difficult to even see, let alone measure them. When looking into the microscope at 100X
(oil immersion), whatever appears to be 1mm in the view is actually about 1 micron.
The log of 10 is used to convert measurements. Ten to any power is ten times itself as
high as the number is. For instance:
104 = 10 X 10 X 10 X 10 = 10,000
10-4 = 1 X (0.1 X 0.1 X 0.1 X 0.1) = 0.0001
Likewise, 10-6 would be equal to: 1 X (0.1 X 0.1 X 0.1 X 0.1 X 0.1 X 0.1) = 0.000001
A table can help explain how small a micron is.
Units of measurement common in the microbial world
Unit Symbol Number Log10
Meter m 1 m 100
Centimeter cm 0.1 10-2
Millimeter mm 0.001 10-3
Micron u 0.000001 10-6
Nanometer nm 0.000000001 10-9
To help put things in perspective, one micron is one millionth of a meter. While looking into the view of the microscope, if a soil particle appears to be 2mm, then it is really 2 microns without the magnification. Clay particles are extremely small (two hundredths of a millimeter), which would be too small to see under oil immersion. However, you might be able to detect clumps of clay. Now figure out how large your soil samples are. Look at a ruler to help you remember the approximate size of a millimeter. Once you have the measurement, convert it to microns.
Silt particle size: ________________
Sand particle size: ________________
Clay particle(s) size: ________________
13. When finished operating the microscope, gently wipe off the 100X (oil immersion)
lens with lens paper. Any material used other than lens paper will scratch the lens.