Day four will teach students how to use microscopes. The instructions are intended for first time microscope users and will introduce the microscopic world to the students. After the students have finished with their field trip lab assignment, prepare three separate jars of sand, silt, and clay. Fill the jars with water, so that there is a high ratio of water to soil. Before beginning the microscope section on day four, be sure to have students mix up their sample. For this assignment you will need to have slides and cover slips available, as well as oil (for 100X microscopes) and a way of extracting small amounts of the soil- water mixture. Plastic pipettes are ideal, but another good way for students to do this would be to use a straw. Place a straw into the soil mixture, cover the top, and then deposit a drop on each slide. Make sure that the soil particles have not settled to the bottom of the jar before extracting. Three drops of each of the sand/ clay/ silt soil mixtures will easily fit on each slide. Grease pencils are often used to outline the area where the mixture will go so that the mixture will not run and contaminate what is next to it. If grease pencils are not available, then the student may want to do only one soil mixture at a time. Other items that are especially fun to look at under the microscope that don’t necessarily correlate to soil are thin onion cells, hair, potato cells, and living organisms from river or creek water. The onion cells have to be sliced extremely thin, and students will be able to identify the cells in a lower magnification, so no cover slip or oil will be necessary. Potato cells are of equal size but are more visible when stained with iodine. Living organisms are extremely small (1-4 microns) but are visible under the 100X magnification. After the students are finished with the microscope section, make sure that lens paper is handy so that they can wipe off the 100X lens with it. After the microscope section, have students take the soil samples they set aside the previous day and have them finish fill in the chart. They may need to answer the conclusion at home if there is not enough time.
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