Practical organic and bio-chemistry / by R.H.A. Plimmer.

  • Robert Plimmer
Date:
1915
Catalogue details

Licence: Public Domain Mark

Credit: Practical organic and bio-chemistry / by R.H.A. Plimmer. Source: Wellcome Collection.

    568/660 page 548
    Acidity. In order to estimate the acidity a sufficient amount of alkali of known strength is added from a burette until neutralisation is produced, as indicated by the colour reaction of phenolphthalein, which has been previously added. It must be remembered that different indicators give different results. Congo red and methyl orange are only affected by strong acids, whereas litmus and phenolphthalein are affected by weak acids, such as carbonic acid. The two former do not react with urine. Procedure. (a) 25 cc. of urine are measured out with a pipette into a flask or beaker and diluted with 50-100 c.c, of water. About 6 drops of phenolphthalein solution are added, and ‘1N sodium hydroxide is run in from a burette until the solution has a permanent and distinct pink colour. Owing to the presence of calcium salts in the urine the ene point is difficult to see. (6) To overcome the difficulty Folin recommends that the titration be carried out inthe presence of neutral potassium oxalate :— 25 c.c. of urine are diluted with an equal volume of water, 15 gm. of finely powdered potassium oxalate, and 4 to 5 drops of phenol- phthalein are added. The solution is shaken for I to 2 minutes to dis- solve most of the oxalate, and whilst the solution is still cold from the effect of the oxalate it is titrated with -1N alkali until a permanent pink tint remains. This neutral solution is used in the estimation of ““ammonia ” (p. 549). As urine contains a mixture of acids the result is not expressed in. terms of any particular acid; but in terms of ‘1N acid either per 100 c.c. of urine or per 24 hours’ quantity (diluted to 2000 c.c.), thus :— | Suppose 2°5 c.c. urine required 4°5 c.c. of ‘IN alkali, the acidity is 18 c.c. per 100 c.c, or 360 c.c. ‘IN per 24 hours’ quantity. Ammonia. The estimation of ammonia in urine until 1902 was a matter of considerable trouble on account of the length of time required to per- form an analysis, but in tat year Folin introduced his zration method for removing the ammonia from urine made alkaline with sodium carbonate. Folin’s Method. The apparatus required for this estimation is the same as that used in estimating urea by means of urease (p. 136). 25 c.c. of urine are placed in the tall gas cylinder together with 1 gm. of anhydrous sodium carbonate and a few c.c. of toluene or paraffin. The cylinder is connected to the receiver containing ro or 20 c.c. of ‘rN acid coloured with a few drops of alizarin red as indicator.
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