So by building up the concentration of ammonium ions inside its retaining membrane, H. pylori is able to fend off the destructive attentions of the hydrogen ions in stomach acid and thus live free from competition by less hardy germs.

ECONOMIST: Stomach turning | The

Car batteries are filled with acid and can give off hazardous hydrogen gas if mishandled.

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These ions, like the hydrogen ions that are the heart of every acid, have a single positive charge.

ECONOMIST: Stomach turning

These are an amine group, an acid group (hence the name), a hydrogen atom, and a fourth chemical group that can be any one of 20 different clusters of atoms.

ECONOMIST: Folding stuff