Modest Experiment In Methane Gas Production
(Page 2 of 3)
March/April 1973
By the Mother Earth News editors
The four-inch manometer dimension shown in the drawing should be considered a maximum for both practical and safety reasons. Filling the tube with water to such a depth will give you eight inches of pressure . . . which is more than sufficient. Gas appliances usually operate on pressures of less than eight inches and there's no reason for you to risk blowing your jug apart with gas compressed beyond this amount.
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Once your manometer is completed, you should make a "burner tip" by drawing out a piece of glass tubing in the approved manner (again, any chemistry student should be able to help you if you've never formed glass tubing before). I made my tip quite long as a precaution against the possibility of a backflash and advise you to do the same. Then attach the stretched-out burner to one arm of your glass "Y" with a short piece of rubber tubing on which a clamp is placed to act as a valve.
The other branch of the "Y" feeds directly to your gas collector through a longer section of rubber tubing (also fitted with a clamp). My collector is a polyethylene milk bag taken from a cafeteria-type dispenser. The cardboard cartons that fit inside such dispensers are thrown out after one use and you'll find that each box contains a bag-liner. Fully inflated, the bags are somewhat larger than a king-sized pillow. I washed one out, rolled it up to expel the air inside and hooked it to my "Y".
Now you're ready to place some manure in the jug. The best type appears to be a mixture of droppings and litter from a chicken barn but, if you can't get that, try something else. I used straight horse manure on my first run and it produced gas. The very most efficient formula, of course, is 30 parts of carbon to one part nitrogen . . . but you can think about that later. Our objective right now is to get your methane experiment moving.
Mix the manure with water to form a slurry and pour it into the jug. (The narrower the container's opening, the more humbling the experience!) Fill the jug to about four inches below the stopper (there'll be some initial foaming and you want to keep it out of the tubing).
The most efficient generation of methane takes place at 90 to 100°F and, if your slurry's temperature drops much below 80°, the gas production will be slow or nonexistent. You'll have to provide a sufficiently warm environment for your jug, then, if you want it to make gas. Bear in mind, though, that methane—carelessly handled—can explode . . . and take suitable precautions in setting up your apparatus. I placed my mini-digester near the furnace and its gascollector bag about five feet away. Enough said.
Start your generator working with all its valves (clamps) closed and, after a couple of days, the water being "pushed" up the long arm of the manometer will indicate that some pressure is beginning to build in the jug. This first production is mostly carbon dioxide, which will not burn. (Test the gas by holding an ignited match at the tip of the burner and opening its clamp. The amount of gas in the manometer is sufficient for such a trial, although—as stated—the carbon dioxide will not burn.)
