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This series of experiments was triggered by the concerns of a number of people about the production of hydrogen sulfide by the microbes breaking down organic waste. We did not feel that it was much of a problem, but hydrogen sulfide is a serious toxic gas, so we wanted to be sure our evaluation was correct (please note: this introduction was written before we did any experiments.) While we were at it we checked for several other gases.
Experiment 1 (December/January1995-6):
Experiment 2 (Unfinished)
Determination of the components marsh gas collected from an Alaskan lake in the winter time, with particular attention paid to hydrogen sulfide.
The materials list can be broken into two parts:
After a short search (see dialog) I found a number of possible bubbles in the ice to obtain samples from. I opened the tops of some of them, to allow them to refreeze and collect more gas, and left some untouched (so I could try to obtain the gas from the bottom).
2 days later I went back. After cutting a hole next to a promising bubble, we attempted to extract it using the hose lashed to the wooden rod (see dialog) without success. We also tried a couple more without any more success so we went to one of the bubbles I'd cut open the previous day.
I poured about 2" of water into the frozen 'basin' made when I'd cut it open previously (the lake surface was about 3.5 higher than the fresh ice since that is as high as the water came the previous day). I took a glass jar (a washed jam jar), filled it with water from the bucket, putting the lid on while it was in the bucket so there was no trapped air. I turned the jar upside down in the 'basin', took the lid off under water and set it off to one side (still upside down filled with water). Taking my pocket knife I carefully started jabbing the thin layer of ice over the hole. Unfortunately I only got a few little bubbles out; not enough to trap. So we went to the next spot. This time we were more successful, and got a small stream of bubbles. I quickly moved the jar over it, and when it was 2/3 full (a little more than 1/4 liter, or 1.5 cups) I moved it away from the bubbles. Then, very careful not to raise the edge of the jar above the water level, I put the lid back on. The bubbles continued to come so I quickly did another 2 jars.
By keeping the jars upside down it maintained a water barrier between the air and the captured gas. We returned home, and I dried and labeled the 3 jars of marsh gas.
Three days later I went back to get another sample. I cut open a previously untouched hole (to get some water) and found I'd caught it bubbling. So I filled a jar with water and held it over the stream of bubbles until it was mostly full. Then I got my water and went to one of the places I'd previously opened (but a different one than where I'd obtained samples). It was short work to obtain a sample from this hole, using the technique outlined above.
While not directly part of this experiment, here is some dialog about the project.
Marsh gas is produced by the anaerobic decomposition of organic materials. It was not possible to obtain samples of the organic materials which were the source of our gas. The temperature where the decomposition was occurring was very close to freezing. The depth of the water, though not measured, is estimated at 5 meters (16 feet). It is unknown how much sediment (silt and/or mud) was over the top of the organic material. Production at the one bubble is very roughly estimated at 1 liter (4 cups)/day. This tells us very little since the amount of material decomposing is unknown. The best bubble we tapped had produced probably 4 liters (1 gallon) per day. It appears that production rises and falls (for unknown reasons), for this particular bubble was not very large (as would have been the case if it had continuously produced 4 liters/day all winter). Other bubbles seemed to have ceased, or nearly ceased, production.
These unknowns are mentioned for consideration, though we feel they have little bearing on our experiment. Our primary objective was to determine if hydrogen sulfide was present. Other gases we expected to find were methane, carbon dioxide and water vapor. There was a good possibility that other gases would be present in trace amounts; we hoped to identify most of these.