Directions for a practical course in chemical physiology / W. Cramer.

  • Cramer, William, 1878-1945.
Date:
1917
Catalogue details

Licence: In copyright

Credit: Directions for a practical course in chemical physiology / W. Cramer. Source: Wellcome Collection.

    28/136 (page 16)
    They are precipitated on neutralising their solutions, and dissolve again in an excess of either acid or alkali. With the diluted egg-white, which represents approxi- mately a 0-5 per cent, solution of ovalbumin and ovo- globulin, carry out the following tests, by which proteins can be recognised. GENERAL PROTEIN REACTIONS. General Protein Tests. Experiment 34. Colour Tests :— (a) Biuret Test.—To a portion of the protein solution add sodium hydroxide so that the solution is strongly alkaline, then one or two drops of very dilute copper sulphate solution. (An excess of copper sulphate must be avoided.) The solution becomes violet. On what group in the protein molecule does this test depend ? Prepare some biuret by heating a few urea crystals in a dry test tube until the melted mass begins to solidify again. Allow to cool, dissolve in a little water, and apply the biuret test. What is the structural formula of biuret ? (b) Millori's Test.—To a portion of the protein solution add a few drops of Millon’s reagent (solution of mercurous and mercuric nitrates). A precipitate forms, which, on heating, becomes brick-red. The red colour constitutes the essential part of the test. On what group in the protein molecule does this test depend ? Repeat with a dilute solution of phenol. Apply Millon’s test to the protein solution after having added some sodium chloride. What takes place ] Explain. Millon’s test can be applied to insoluble proteins. (c) Xanthoproteic Test.— To a few c.c. of the protein solution add one-third of its volume of strong, pure, nitric