Sciencemadness Discussion Board

Farting in the bath

CrimpJiggler - 12-8-2014 at 14:25

I notice that when I fart in the bath it always smells different, it smells like cabbage, whereas out in the open I get the rotten egg scent. I'm guessing the rotten egg smell is hydrogen sulfide and it gets dissolved in the water because its relatively polar. Whats the cabbage smell? Is it methane? I know they add sulfur compounds to natural gas to make it detectable because natural gas is relatively odourless, so I assumed methane doesn't have much of a smell to it. I suppose there are a lot of compounds present in fart, the smell varies depending on what you ate. It sounds like a ridiculous topic, but I'm guessing thats just to the average person, to chemists this is fairly fascinating stuff.

Loptr - 12-8-2014 at 15:18

Question: What Is the Chemical Composition of Farts?

Farts are the common name for flatus or flatulence. Have you ever wondered what farts are made of and whether they are the same for everyone? Here's a look at the chemical composition of farts.

Answer: Have you ever wondered about the chemical composition of farts, or to be more technical, flatus? The exact chemical composition of human flatulence varies from one person to another, based on his or her biochemistry, the bacteria inhabiting the colon and the foods that were eaten. If the gas results from ingesting air, the chemical composition will approximate that of air. If the fart arises from digestion or bacterial production, the chemistry may be more exotic. Farts consist primarily of nitrogen, the principal gas in air, along with a significant amount of carbon dioxide. A typical breakdown of the chemical composition of farts is:

Nitrogen: 20-90%
Hydrogen: 0-50% (flammable)
Carbon dioxide: 10-30%
Oxygen: 0-10%
Methane: 0-10% (flammable)

Lighting Farts on Fire - The Blue Flame
Human flatus may contain hydrogen gas and/or methane, which are flammable. If sufficient amounts of these gases are present, it's possible to light the fart on fire. Keep in mind, not all farts are flammable. Although flatus has great YouTube fame for producing a blue flame, it turns out only about half of people have the archaea (bacteria) in their bodies that are necessary to produce methane. If you don't make methane, you may still be able to ignite your farts (a dangerous practice!), but the flame will be yellow or possibly orange rather than blue.

The Smell of Farts
Flatus often stinks! There are several chemicals that contribute to the smell of farts:

skatole (by-product of meat digestion)
indole (by-product of meat digestion)
methanethiol (a sulfur compound)
dimethyl sulfide (a sulfur compound)
hydrogen sulfide (rotten egg odor, flammable)
volatile amines
short chain fatty acids
feces (if present in the rectum)

The chemical composition and thus odor of farts differs according to your health and diet, so you would expect a vegetarian's farts to smell different from those produced by a person who eats meat.

[Edited on 12-8-2014 by Loptr]

bismuthate - 12-8-2014 at 17:02

Perhaps soap in the water reacts with the sulfides? It seems unlikely though

DistractionGrating - 12-8-2014 at 20:40

+1 CrimpJiggler's question. I've noticed this ever since I was very young. Always wondered about it. If there is anyplace online that this question might be taken seriously, it's here! I'd like to know what happens to flatulence as it bubbles through bath water that makes it smell noticeably differently than un-bath-water-filtered flatulence.

12AX7 - 12-8-2014 at 22:28

Kind of funny to observe that farts arise from a, shall we say, humid environment to begin with. So what difference could more water make, anyway?

I've noticed the effect before, too, so apparently the answer is, at least a bit of difference. Probably picking up the more soluble and polar parts (like hydrogen sulfide, amines), leaving the nonpolar components (indole and related, organic thiols/sulfides, etc.). And also picking up a bit of gas from the water itself, which if it's city water, will include a little chlorine, or pool water, even more.

What that, in turn, smells like, who knows (nose) -- a 'bouquet' of chemicals can smell quite different from small changes in composition. We're also talking chemicals with very small concentration to begin with (<= ppm), and with sensitivities going into the ppb and even ppt. So the amount and rate of solubility of any given compound, and its effect on the odor, need not be very predictable!


kt5000 - 20-8-2014 at 21:45

Quote: Originally posted by Loptr  

skatole (by-product of meat digestion)
indole (by-product of meat digestion)
methanethiol (a sulfur compound)
dimethyl sulfide (a sulfur compound)
hydrogen sulfide (rotten egg odor, flammable)
volatile amines
short chain fatty acids

Someone's masters thesis right there..

Praxichys - 21-8-2014 at 04:34

I have noticed that farting into a seat made of open-cell foam causes different rates of gas diffusion separate the fart components over time, resulting in some sort of hellish form of gas chromatography. At first it is sulfurous and sharp, followed by the deep fishy faeces stink of the heavy amines as you shift your seating position a minute or two later.

An experimental note: Further progress is limited because the girlfriend says I am banned from eating horseradish.