Laboratory outlines for physiology / Michael F. Guyer and William O. Pauli.

  • Michael F. Guyer
Date:
1906
Catalogue details

Licence: In copyright

Credit: Laboratory outlines for physiology / Michael F. Guyer and William O. Pauli. Source: Wellcome Collection.

    12/92 page 10
    2. BIURET TEST. To another portion of the albumen solution add an equal volume of a concentrated solution of sodium hydrate, to make It strongly alkaline, and heat to boiling. Add one to two drops of a very dilute solution of copper sulphate: a pink to violet color is obtained. 3. MILLON'S TEST. To a portion of the albumen solution add only a few drop.s of Millon’s reagent (a solution of mercuric nitrate to which is added a little nitrous acid). A white precipitate forms, which on boiling for two or three minutes forms a brick-red coagulum. d. HELLER’S TEST. To some of the albumen solution carefully add an equal volume of concentrated nitric acid, so that the two liquids do not mix. (It is best to use a pipette). A white cloud forms at the zone of contact. If the liquids are mixed and warmed gently, the egg albumin is coagulated by the nitric acid. 5. HEAT COAGULATION. Heat some of the albumin solution in a test tube; it is pre- cipitaed as a coagulated proteid which is insoluble. G. PRECIPITATION BY AMMONIUM SULPHATE AND OTHER NEUTRAL SALTS. To some of the egg albumin solution add an equal amount of a saturated solution of ammonium sulphate; a white precipitate is formed. Full saturation with ammonium sulphate precipitates all proteids except peptone. The globulins are precipitated by certain salts, like magnesium sulphate, which do not precipitate the albumins. A coagulated proteid differs from a precipitated proteid in that it can not be restored to the soluble form by treat- ing with suitable reagents. 7. LOOSELY COMBINED SULPHUR. To 5 cc. of 20 per cent caustic potash solution add a few drops of lead acetate solution; a precipitate forms which redissolves on shaking. Add a little egg albumin solution and boil. A brown to black color will develop, due to the formation of lead sulphide. 8. TEST FOR NITROGEN. To a few fragments of dry albumin (e. g., dried white of egg) add an excess of soda-lime and heat in a dry test-tube. What is the effect of the vapors upon red litmus-paper? Note the odor. The presence of ammonia proves that the albumin contained nitrogen. PHYSIOLOGICAL SIGNIFICANCE OF PROTEIDS. Proteids constitute the essential chemical and physical basis of living substance. In man they form about one-sixth of the weight of the body.
    digitised image 1
    digitised image 2
    digitised image 3