Why should acetylene gas cylinders used for gas welding be erected in upright position?

Why should acetylene gas cylinders used for gas welding be erected in upright position?

Acetylene gas is commonly used for gas welding because of its simplicity of production and transportation and its ability to achieve high temperature in combustion (e.g. around 5,000oF). Acetylene is highly unstable and flammable and would explode in elevated pressure when reacting with oxygen in air. Storing acetylene gas in cylinders under pressure is very dangerous. Hence, for welding purpose, gas acetylene is stored in cylinders of liquid acetone contained in porous material (like firebrick) to enhance there is no free space left for acetylene gas and for cooling purpose in the event of thermal decomposition. It also prevents the formation of high pressure air pockets inside the cylinder. Dissolved acetylene in acetone will no longer in contact with oxygen and is not subject to decomposition. On the other hand, acetone is used because it is capable of dissolving large amount of acetylene gas under pressure without changing the nature of the gas.The cylinders for gas welding i.e. oxygen cylinders and acetylene cylinders, when not in use should be stored separately because any mixture of these gases resulting from accidental leakage can be highly explosive. When in use, acetylene cylinders should always be kept in upright position because acetone liquid will be drawn from the cylinders with the gas if they are kept horizontally. Consequently, significant leakage of acetone liquid will result.

Note: Oxygen and acetylene gas cylinders are commonly used in construction sites for gas welding.