Why should an acetylene bottle not be used in the horizontal position?

Using an acetylene bottle in the horizontal position is not advisable because acetylene is stored in a solvent, typically acetone, which absorbs the gas and allows it to be stored under pressure. When the cylinder is placed horizontally, there's a risk that acetone could be drawn out along with the gas when it is being used. This could lead to an improper gas mixture, potentially resulting in unsafe operating conditions and inadequate combustion.

It’s vital to maintain the integrity of the acetylene supply, which is why the bottle is designed to be used upright; this ensures that only acetylene gas is released, while the acetone remains within the cylinder. This practice helps in maintaining safety and efficiency during welding operations.