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The U.S. Department of Agriculture produces a gas cartridge to poison subterranean rodents. The product is provided as a cardboard tube sealed at one end and then loaded with a mixture of 144.6 grams of the following ingredients:

53.0% Sodium Nitrate 28.0% Charcoal 19.0% Inert Ingredients

Once filled, the cardboard tube is sealed at the other end with a thin cardboard cap which can be punctured and a fuse inserted when ready to be used. The gas cartridge's advertised function once lit is to generate a large volume of carbon monoxide that kills the rodent within a few minutes in its burrow. My experience has been it is very effective when used according to the instructions.

The USDA gas cartridge is getting harder to obtain anymore and a commercial producer sells a similar product which is utilized in the same applications. But it is smaller and uses a somewhat different formulation. It does not advertise how the rodent is poisoned, so I don't know if the resulting gas from combustion is primarily CO or something else. My experience has been that it doesn't seem to be as effective as the USDA gas cartridge, but I don't know if it is because of its different formulation or just its smaller size. The 56.7 gram mixture of ingredients in this commercial gas cartridge are as follows:

50.0% Sodium Nitrate 38.0% Sulfur 9.0% Charcoal 3.0% Inert Ingredients

The question is how much carbon monoxide is generated by each of these cartridges when their ingredients are ignited and what are the quantities of other resulting gases? Just straight theory here is good enough for me. I know there are probably variables such as how well the ingredients are ground and mixed and what are used as the inert ingredients in each. But lets just leave those variables out of the equation.

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  • $\begingroup$ Straight theory would not tell you much, as long as you are leaving out the crucial variables. That being said, the latter cartridge seems to be acting primarily via $\ce{SO2}$, not $\ce{CO}$. Both are deadly; which death is better, I'm not sure. $\endgroup$ – Ivan Neretin Dec 22 '15 at 21:24
  • $\begingroup$ I think the CO is probably more humane although it looks like it takes much less Sulfur Dioxide than Carbon Monoxide to result in an effect that is Immediately Dangerous to Life or Health at 100 ppm versus 1200 ppm. See my comment below. $\endgroup$ – John Hall Dec 22 '15 at 22:55
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About the best that can done is simply to look at the ratio of carbon in the two cartridges.

$\dfrac{56.7*0.09}{144.6*0.28} = 12.6$%

The ratio of carbon dioxide to carbon monoxide formed on burning would depend on particle size, how well mixed an so on. The second formulation with sulfur is akin to black gun powder. The sulfur burns first at a lower temperature to ignite the charcoal. The sulfur dioxide would be toxic as well, but not as fast acting as carbon monoxide.

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  • $\begingroup$ It looks like the IDLH for carbon monoxide is 1200 ppm where for sulfur dioxide it is 100 ppm. IDLH is an acronym for Immediately Dangerous to Life or Health, and is defined by the US National Institute for Occupational Safety and Health (NIOSH) Assuming rodents may react similar to humans, it looks like sulfur dioxide would be toxic in much lower concentrations than CO. This may explain why the commercial manufacturer uses a smaller quantity of ingredients. Maybe the better results I see with the U.S.D.A gas cartridge does have something to do with the inert ingredients. $\endgroup$ – John Hall Dec 22 '15 at 22:49
  • $\begingroup$ Well if the "inert" ingredients increase the lethality, then they really aren't inert are they? $\endgroup$ – MaxW Dec 22 '15 at 22:58
  • $\begingroup$ You would think that would be true. I read somewhere that the inert ingredients are usually the binder, whatever that is. But with 19% inert ingredients in the U.S.D.A cartridge, you kind of have to question why that is so high. Is it something that allows for more complete combustion of the primary ingredients. And if that is the case, could you really call it inert? For example, if water was one of the ingredients, could that be classified as inert on the label when it may actually contribute to more efficient combustion? Do you have any other theories? $\endgroup$ – John Hall Dec 23 '15 at 0:56
  • $\begingroup$ I would really believe that the scientists creating such a mix understood what they were doing. So I'd assume that inert really meant inert relative to the purpose. $\endgroup$ – MaxW Dec 23 '15 at 1:04
  • $\begingroup$ Maybe the inert materials slow down the combustion process as opposed to participating in it so you get a longer burn time as opposed to a "flash in the pan" so to speak that might burst the cartridge and blow some of the material away before it has a chance to ignite. $\endgroup$ – John Hall Dec 23 '15 at 4:41

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