Archive image from page 187 of Dairy chemistry; a practical handbook. Dairy chemistry; a practical handbook for dairy chemists and others having control of dairies dairychemistryp00rich Year: 1920 172 THE ESTIMATION OF PROTEINS. caustic soda, followed by 10 of a 10 per cent, solution of potassium sulphide, or 1 gramme of sodium hypo phosphite, are added through the dropping funnel, and the contents of the flask mixed by rotatory shaking ; a flame is placed beneath the distillation flask, cold water run through the condenser, and the contents distilled till about 200 have passed ove
Archive image from page 187 of Dairy chemistry; a practical handbook. Dairy chemistry; a practical handbook for dairy chemists and others having control of dairies dairychemistryp00rich Year: 1920 172 THE ESTIMATION OF PROTEINS. caustic soda, followed by 10 of a 10 per cent, solution of potassium sulphide, or 1 gramme of sodium hypo phosphite, are added through the dropping funnel, and the contents of the flask mixed by rotatory shaking ; a flame is placed beneath the distillation flask, cold water run through the condenser, and the contents distilled till about 200 have passed over. The tap of the dropping funnel is opened, the flame removed, and the flask disconnected from the condenser ; after washing the latter into the flask containing the distillate, the distillate N is titrated with — alkali solution, using methyl red or cochineal Fig. 24.—Kjeldahl Apparatus. as indicator. An amount of acid equivalent to the alkali used is subtracted from the amount of acid originally added; the difference represents the acid neutralised by the ammonia distilled. From this figure should be subtracted the figure obtained in a blank experiment—, an experiment performed without the addition of milk, but in other respects exactly the same. Each of — acid neutralised by the ammonia produced is equal to 0-0014 gramme of nitrogen. The percentage of nitrogen multiplied by 639 will give the percentage of total proteins. Another form of apparatus gives equally good results if care be used ; the caustic soda and sulphide solution are poured carefully down the side of the distilling flask, so that the alkaline solutions do not mix with the acid ; the bulb tube rapidly inserted, and the contents of the flask mixed. No condenser is used, but the flask containing the standard acid may be placed in cold water (Fig. 24),
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