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.

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    Test with the biuret test for the absence of proteins before applying the tests for carbohydrates. If, however, Molisch’s test (Exp. 15) is applied to the egg-white solution (still containing proteins), a positive result is obtained. This shows that while no free carbo- hydrate is present in the white of egg, the protein of egg- white contains a carbohydrate group chemically bound in its molecule. MILK. Experiment 40.—Test the fresh milk with litmus paper. The reaction is either faintly alkaline or amphoteric (be., turns blue litmus red and red litmus blue). Determine the specific gravity of milk. Record. Why has skimmed or separated milk a higher specific gravity than fresh milk ] Eat. Experiment 41. Separation of Constituents.—Extract the fat by shaking 5 c.c. of milk in a test tube with twice its volume of ether. Pour off the ether and allow to evaporate until only a few drops are left. Pour these on to a filter paper. A greasy spot indicates the presence of fat. Caseinogen. Dilute 20 c.c. of milk with 80 c.c. of water. Add care- fully dilute acetic acid drop by drop, stirring the fluid after each drop has been added, until a flocculent pre- cipitate is formed, and the solution in which it floats appears clear. An excess of acid must be careful] y avoided, as it would dissolve .the precipitate. The pre- cipitate consists of caseinogen —the main protein of milk— with adherent fat. Filter. With the precipitate, carry out the experiments described below under caseinogen (Exp. 43).