A rechargeable battery technology that dates back to the mid-1800s. Liquid-filled lead acid batteries are used in vehicles, but gel-filled units, which came out in the early 1970s, provide the most ...

Citric acid is a weak organic acid that occurs naturally in produce, such as citrus fruits. It is used in food, cosmetics, and cleaning products. Share on Pinterest vkbhat/Getty Images Citric acid is ...