It's uemura again...
He found the write-up for the calculation of the percentage of a h2o2 solution. This extract comes from a paper on growing shrooms with the help of peroxide which allows a kind of 'sloppy' technique instead of working in a clean and sterile environment.
Here it is:
Here is my method for getting a
rough measurement of peroxide: Get a clean test tube (preferably one with a lip or screw cap), a small birthday-party type balloon, and a slice, small enough to fit into your test tube, of the stalk of any mushroom you have handy (for best results, use a young, rapidly growing mushroom and take a piece of stalk, trimming off the natural skin to expose plenty of broken cells). If you don’t have any mushrooms, a piece of banana or other skinned vegetable should do just as well)
MnO2 works as well! . You will also need your peroxide solution, a rubber band, a pasteurized measuring pipette, a 100 ml graduated cylinder, and a pot of water.
1) With the pasteurized measuring pipette, withdraw 5 ml of the peroxide solution from the bottle and transfer it into the test tube.
2) Place the slice of mushroom in the upper part of the tube (don't let it slip into the peroxide yet).
3) Make sure the balloon is empty of air and stretch the mouth of the balloon over the mouth of the tube (tilt the tube to keep the slice of mushroom from slipping into the solution until the balloon is in place.
4) Put a rubber band around the mouth of the balloon on the tube, to keep gas from escaping as the pressure builds (I have found it most effective to use a broken rubber band that can be wound tightly around the threads of the tube, over the mouth of the balloon).
5) Once the balloon is sealed in place, let the mushroom slice slip down into the peroxide solution. The solution should begin bubbling oxygen immediately.
6) Agitate the tube. The peroxide solution should be largely decomposed in five to ten minutes, depending on the amount of catalase/peroxidase in your mushroom slice.
7) When decomposition is almost complete, you'll see that the bubbling will have slowed and the bubbles will have become quite small. Meanwhile, the balloon should have become taut as it began to fill with released oxygen.
Now, my college chemistry training tells me that 5 mls of a 3% solution of hydrogen peroxide should generate about 49 mls of oxygen when the peroxide decomposes completely at room temperature and one atmosphere pressure. To measure the oxygen released from your peroxide solution:
1) Fill a graduated cylinder with water and turn it upside down in a pot of water, making sure all bubbles are out.
2) Twist the balloon on your test tube to trap the released oxygen, remove the balloon from the tube holding the twist tightly, and put the balloon under the water in your pot.
3) Carefully release the gas from the balloon up into the inverted graduated cylinder, displacing the water inside it.
4) Keeping the open end of the cylinder under water, read the volume of oxygen off the graduated cylinder.
The first time I did this, I got 52 mls of gas inside my graduated cylinder from 5 mls of peroxide solution. Given that there may well have been about 3 mls of air in the flat balloon before I started, the peroxide solution probably generated pretty close to the theoretical amount of oxygen for 5 mls of 3% solution.
Here’s how to calculate the amount of peroxide solution you will need, if you solution tests higher or lower than 3%:
1) Divide the volume of oxygen expected for 5 mls of 3% solution (49 mls if the balloon is completely empty to begin with, or 52 mls in the above example, counting the few milliliters of air initially trapped in the balloon) by the volume of oxygen you actually got.
2) Multiply the previous number by the volume of peroxide solution you would add to your medium or substrate if it were really a 3% solution (this volume is given in appropriate section of this manual, for instance, in the section on agar culture, you will find that you would need to add 6 mls of 3% peroxide for 1 liter of pressure-cooked agar medium).
Carpe Diem
