Hydrolysis of nitriles

Nitriles can be viewed as primary amide which has lost a molecule of water:

Reacting a primary amide with a dehydrating reagent is one way nitriles can be made.

Likewise, nitriles can be made into primary amides by acid-catalysed hydrolysis. Mechanism:

Of course we also know that if the conditions are vigorous enough, the amide will hydrolyse into a carboxylic acid and ammonia. So overall a long acid reflux can turn a C≡N into a COOH.