starch in a cereal or similar substance can be completed within two hours. The chief amount of time saved is in the heating with the malt extract, which instead of being continued for two hours, as usually directed, can be accomplished in thirty minutes.[159] =192. Precipitation of Starch with Barium Hydroxid.=—The tendency of carbohydrate bodies to unite with the earthy bases has been utilized by Asboth as a basis for the quantitive determination of starch.[160] About three grams of the finely ground sample containing the starch, or one gram of pure starch, are rubbed up in a mortar with water and the detached starch remaining suspended in the wash water is poured off. This operation is repeated until all the starch is removed. In difficult cases hot water may be used. The starch thus separated is heated in a quarter liter flask to the boiling point to reduce it to the condition of paste. When the paste is cold it is treated with fifty cubic centimeters of the barium hydroxid solution, the flask closed and well shaken for two minutes. The volume is then completed to the mark with forty-five per cent alcohol, the flask well shaken and allowed to stand. In a short time the barium-starch compound separates and settles. Fifty cubic centimeters of the clear supernatant liquor are removed with a pipette, or the liquor may be passed through a filter and the quantity mentioned removed for titration of the residual barium hydroxid after the addition of a few drops of phenolphthalein solution. The quantity of barium hydroxid remaining, deducted from the original quantity, gives the amount which has entered into composition with the starch; the composition of the molecule being BaOC₂₄H₄₀O₂₀, which contains 19.10 per cent of barium oxid and 80.90 per cent of starch. The set solution of barium hydroxid must be preserved from contact with the carbon dioxid of the air. The burette should be directly attached to the bottle holding the set solution, by any of the usual appliances, and the air entering the bottle must be deprived of carbon dioxid. The water used in the work must be also free of air, and this is secured by boiling immediately before use.