Conductivity and hardness changes in aged compacts.

Batches of sodium, potassium, and ammonium chloride tablets containing no excipients and spray-dried lactose tablets containing 0.5% magnesium stearate were stored at 20 and 76% relative humidity. Electrical resistance and hardness measurements were made within 1 hr after compression and at intervals during a 45-day period. Hardness values of sodium, potassium, and ammonium chloride tablets stored at 20% relative humidity increased from 70 to 200% at 45 days, while conductances decreased 10-fold. Tablets stored at 76% relative humidity showed no increases or slight decreases in hardness with slight increases in conductance. Lactose tablets decreased slightly in hardness with corresponding increases in conductance.