What did soldiers put on a handkerchief to protect themselves from poison gas?

Soldiers during World War I often soaked handkerchiefs in solutions of sodium bicarbonate or vinegar to create a makeshift gas mask against poison gas. These substances helped neutralize certain toxic gases, providing a temporary layer of protection. Additionally, some soldiers used charcoal or other absorbent materials to enhance the handkerchief's effectiveness. However, these methods were far from perfect and highlighted the urgent need for more effective gas masks.