Analytic Essay


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 Analytic Essay

Five-Gas Diving Mixture

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In this experiment, we tried to determine if nitrogen or oxygen caused
"The Bends" in blood more rapidly. As happened with the discovery of
antibiotics, we accidentally discovered another phenomenon, Dalton's Law.
Dalton's Law says that the pressure of a gas is a result of the partial
pressures that make up that gas. Using Dalton's Law, we found that in causing
"The Bends," the dominance of one gas in the mixture plays a larger role in
causing "The Bends" than the type of gasses in the mixture.
This observation
inspired us to devise, in theory, a better diving mixture.

Experiment Set-up:
We tried to find which combination of gasses cause "The Bends" fastest.
Since we would have trouble finding a person willing to get "The Bends," we
had to use several substitutes. In our experiment, the two-liter plastic
bottles represent the human diver. The one liter of water in the bottle
represents our blood and skin tissue. The gasses we pumped into the bottles
are smaller amounts of the gas which a diver might be diving with. So we
pumped these gasses at a high pressure into the bottles half-filled with
water, and let them sit for several days to simulate the pressure of water on
a diver while underwater. Then we opened the bottle to create a pressure

Effects & Analysis Of Differences In The Mix:
In completing this experiment, 100% Oxygen had the most bubbles dissolve
out of the liquid; Air (80% Nitrogen, 20% Oxygen) had the second most bubbles
escape; and Nitrox (60% Nitrogen, 40% Oxygen) had the least amount of bubbles
dissolve out. These results justify Dalton's & Henry's laws, which explains
when combined, that the greater percentage of Nitrogen that makes up a gas,
more Nitrogen will dissolve out of the bloodstream if a fast reduction in
pressure occurs. Air itself is 80% Nitrogen, which the body can't extract
energy from. So if the pressure of the bottle was at 50 psi (like our
experiment), 40 psi of pressure in the bottle would be attributable to
Nitrogen. When a fast reduction in pressure occurs (opening the bottle), a
higher quantity of that Nitrogen will bubble out of the water than oxygen
because Nitrogen is the dominant gas in the mixture. The more dominant a gas
is over another substance, the higher percentage of gas will dissolve out of
water in a pressure reduction. So a two-gas mixture might have 10% of itself
dissolve out of the water/blood in a pressure reduction, whereas a single
diving gas might have 20% of itself dissolve out of the water/blood during a
pressure reduction. This means a bottle filled with 100 psi (80 psi Nitrogen,
20 psi Oxygen) will have nearly the same effect as a bottle filled with 80
psi of pure nitrogen. The oxygen will cause several bubbles to form, but
nothing noticeable in comparison to the Nitrogen. Dalton's Law explains how
these different gasses dissolve totally separately from each other. This
means, in causing "The Bends," that an evenly distributed five-gas diving
mixture causes nearly the equivalent amount of bubbles as one of the five
gasses itself, or 20%. We can also conclude that a single diving gas does
cause 100% of the bubbles because there is only one gas, so it will have the
largest possible percentage dissolve out of the liquid. One could conclude
that a five-gas mixture should allow a diver to stay underwater five times as
long as a single diving gas.

100% Oxygen Testing:
One ironic error is that both scientists and Jay and I found is that 100%
Oxygen is the worst diving gas, but for separate reasons. We found this
causes "The Bends" fastest because it is the purest concentration of one gas,
which means the largest amount of bubbles will form in a pressure decrease.
Scientists have concluded 100% Oxygen would be the worst diving gas because
at concentrations up to 90% and 100%, Oxygen itself is a poison. Over time or
a certain pressure, a diver would die of seizures.

Logistical Problems With The Experiment & Alternatives:
There were ways we could have made the experiment more complete, and also
more accurate. To not only prove that the dominance of a gas matters more in
a mixture in causing "The Bends" than the type of gasses that make up the
mixture, we could also have tested pure Nitrogen. This extra experiment would
allow us to determine whether Nitrogen or Oxygen molecules cause "The Bends"
faster than the other. Since we previously concluded that quantity of the gas
matters more in causing "The Bends" than the type of gas, the error in
filling the bottle with such large amounts of pressure would out-weigh the
difference in causing "The Bends" between the two pure gasses.
Obtaining Pure Nitrogen:
Not only is pure Nitrogen hard to find and expensive, we would have to drive
deep into Long Beach for the nearest Diving Training Facility. So in many
ways, our lab group set up the best experiment possible under the
The other problem with our lab that no matter how hard we tried, stopping
leaks is hard. In finding nine valid tire valves, leaking is inevitable
because nine bottles can't all stay at 50 psi for 3 days without pressure
eating away at our sealant or a leak occurring in the threaded top. We had to
pump bottles up to 50 psi (higher pressure than car tires are filled up
with), and sustain that psi for several days. This took three attempts.
First, our valve wasn't air-tight. We were recommended a sealant named
"Goop." We had to purchase American Valves and re-do the experiment. The
second time, the valves themselves couldn't hold enough pressure. We had to
get Schrader Valves (1/8 of an inch), and re-do the experiment. After we
filled the bottles the third time, only three leaked. We let it sit for three
days; by then the gasses had dissolved into the water. To create a pressure
change, we opened the bottle and recorded the results.

In conclusion, we found that the dominance of a gas in the mixture
matters more in causing "The Bends" than the gas types in the mixture.