OBJECT:

To make a straw Hydrometer.

MATERIALS:

Safety Goggles, One clear plastic drinking straw, Two pairs of pliers, A match, Some amount of salt for ballast, A narrow metric strip, creased to fit the straw, Folded piece of paper to pour the salt into the straw, A small plastic bottle, ( 16 fluid oz. ) A piece of wire, about a foot long, for adjusting the metric strip. A plastic gallon of water ( with the top removed, but with the handle intact )

PROCEDURE:

1. Work area, kitchen sink.

2. Holding your straw horizontally with a pair of pliers, ( see above diagram ) half an inch from the end.

3. Hold a lighted match, for about a second, to melt the end of the straw, drop your blown out match into the sink, and quickly grab your other pliers and squeeze the melted end to seal it. Try to grab the melted end of the straw with the widest side of the pliers. Allow a few seconds for the straw to cool off. You may have to trim the melted side, but be careful not to cut any holes in the seal.

4. Place your creased Metric strip next to the straw, trim your Metric strip ( from the 30 cm end) , so that it is about one and a half inches shorter then the end of the straw. Insert your metric strip into the straw.

5. Use your empty plastic soda bottle to hold the straw, pour a small quantity of salt onto a piece of folded paper ( one inch by three inches ), pour the salt into the straw. Remember, you are working in the sink, so you don't have to worry about spilling the salt. After you reach the three quarter level, stop pouring the salt. ( When you pour the salt into the straw, try to have the letters pressing against the wall of the straw. ) Now, obtain another bottle filled almost to the top, with water, or remove your straw and find another resting place for it. Rinse the plastic bottle of the salt and fill almost to the top.

6. Now, place the straw with the salt in it, into the bottle filled with water, and see if it floats vertically, you may have remove a little or add a little salt to get it to float vertically.

7. Once it is floating vertically, you now have to adjust the metric strip inside the straw with a small piece of wire. The wire should be slightly bend at the very tip, but free to enter the straw, so it could be used to grab and hold of the side of the metric strip and moved up and down.

8. Adjust you metric strip, so that when it is floating, the metric strip is ending up on a whole number, and remember it is a lot easier to with draw the metric strip, then it is to force it down below the salt. You have to remember that the adjustment is made in reference to the water level and not the salt level.

9. Once you have made your adjustment, you are ready to seal the open end of the straw. Using your pliers again, repeat the steps # 2 and # 3.

OBSERVATION:

1. Record you number when it is floating in clean water.

2. Obtain another gallon plastic bottle, with the top removed, so it act like a small bucket, add one small bottle of water ( 16 fluid oz. ) , to the gallon plastic bottle, using a measuring cup, measure a half cup of salt, and try to dissolve it into the water in the " small bucket " the result should be a saturated solution of salt water, there should be visible some salt crystals in solution.

3. Fill the small bottle with the saturated salt solution, insert your hydrometer and record the new level.

QUESTIONS:

1. How many centimeters difference is there between the clean tap water and the saturated salt solution ?

2. You may want to test other liquids, such as rubbing alcohol, cleaning ammonia solution, BE SURE TO CLEAN YOUR HYDROMETER, EVERY TIME YOU USE IT IN A NEW SOLUTION ! Don't forget that every time you make a measurement, using the hydrometer, you are contaminating that liquid.

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