This method is rarely used in modern laboratories.
WORD CHOICE: WORD CHOICE: rarely, seldom, hardly, scarcelyRarely and seldom both mean 'not often'. Seldomis more formal or literary• People rarely ask questions.• She was seldom seen in public. • The disease is rarely fatal. Hardly and scarcelyboth mean 'almost not' or 'only just'. For example, if you hardly had time to do something, you almost did not have time. Scarcely is more formal or literary• I hardly had time to ask her name.• We had scarcely arrived when he asked us to leave. Hardly and scarcelycan also be used with 'ever' to mean 'not often, almost never', with 'any' to mean 'very few, almost none' etc• I've got hardly any money left.• Hardly anyone agreed with her. In speech, it is usual to say that you hardly everdo something, rather than that you rarely do it• I hardly ever go to the cinema.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.