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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    Experiment 15. Molisch’s Test.—To a few c.c. of the solu- tion add a few drops of an alcoholic solution of a-naphthol. Incline the test tube and allow about 5 c.c. of concentrated sulphuric acid to how down the side of the tube so that the acid settles at the bottom of the tube. At the junction of the two liquids a green ring may at first be formed (if traces of nitrates are present in the sulphuric acid), and above this, in a short time, a reddish-violet ring. The green ring, if present, must be disregarded. If the two liquids be mixed and cooled by gently shaking in running water, so that excessive heating is prevented, the mixture assumes a bluish red or dark blue colour. [All carbo- hydrates and some proteins give this reaction. The test is used to demonstrate the presence of a carbohydrate group in proteins. ] Use of Polarimeter. Experiment 16. Optical Activity. Polarimeter.—Ex- amine by means of a polarimeter the effect of the glucose solution on polarised light. Proceed as follows.1 * * Examine the polarimeter. It consists of a hollow brass tube which, at the one end, contains a Nicol prism, the “ polariser,”- together with a double quartz plate. At the other (upper) end of the brass tube and attached to it by means of a hinge and a spring catch, is another Nicol prism, the “analyser,’1 together with a small telescope and a graduated arc divided into whole degrees. The “ analyser ” can be rotated by means of a milled head. The rotation can be read accurately to a tenth of a degree by means of a vernier. Lock the hinged part and place the instrument so that 1 The following description applies to a polarimeter of the Soleil type, and more particularly to the hand-polarimeter supplied by Winkel, Gottingen. 4