Sentence:  Molten glare singed their eyelids an angry crimson ; suffocating air sapped their strength and strained their nerves to snapping ; dust choked their throats and lay like <WSD>acid</WSD> in their lungs . 
Meaning of the word marked with <WSD> tags:  any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt