Phosphorous Acid is prepared by exposing phosphorus dining soma weeks to the ordinary temperature of the atmosphere. Even in winter the phosphorus undergoes a slow combustion, and is gradually changed into a liquid acid. For this purpose it is usual to put small pieces of phosphorus on the inclined side of a glass funnel, through which the liquor that is formed drops into the bottle placed to receive it. From an ounce of phosphorus about three ounces of acid liquor may be thus prepared.