Question: Is there any pure, gaseous acetylene in the cylinders?
Answer: Yes, there is.
Question: Does the acetylene evaporate from the acetone within the cylinder?
Answer: Yes, it does.
Question: How this happens?
Answer: In the very first moment, acetylene molecules leave the acetone solution and go to the gaseous phase within the cylinder. In a few minutes, though, the equilibrium between the gaseous acetylene and the acetylene in solution is reached and the evaporation stops.
Question: What does it means that the "equilibrium is reached"?
Answer: It means that the quantity of molecules that leave the solution as gas equals the quantity of gaseous molecules that return to the acetone solution.
Question: When is the equilibrium reached?
Answer: When the absolute pressure of the gaseous acetylene equals the vapor pressure of the acetylene in solution.
Question: What does the vapor pressure of acetylene in solution depends from?
Answer: It depends from the temperature the cylinder is at. "Ambient" or "Room" temperature means little in this case. Ambient temperature in the north of Canada could reach 40 F below, whereas here in Brazil it could reach (and in fact it does very often) 100 F above.
Question: Where can I find the relationship between temperature and vapor pressure of the acetylene solution in acetone?
Answer: In a good engineering handbook, or alternatively, asking acetylene manufacturers, such as Praxair, AGA, Linde, Air Liquide, BOC, and others.
Question: Why does acetylene get unstable at 15 psi?
Answer: The unstability of acetylene is not due to pressure but to the shocks and blows the cylinder is subjected to. In fact, acetylene cylinders support a rough treatment in shops and jobsites.
Giovanni S. Crisi
Sao Paulo - Brazil
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