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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    some water, previously heated in a test tube, to replace the water which has evaporated, (a) What change do you observe in the appearance of the starch solution ? Remove every five minutes about 5 c.c. of the solution by means of a pipette, place in a test tube, cool, and test with a drop of dilute iodine solution, (b) Record the results obtained in each case. Continue boiling the bulk of the solution in the flask until the iodine test is negative, i.e., until a drop of dilute i dine solution, when added to about 5 c.c. of the solution, removed from the flask and cooled, fails to produce a colour. This point will be reached after about thirty minutes; the time of boiling required - varies with the concentration of the starch paste and of the acid. The solution thus obtained is used for Experiments 8-16. (c) What has taken place ? Preparation of Alcohol by Fermentation of Glucose. Experiment 8.—(a) To about 15 c.c. of the glucose solution obtained in Experiment 7 add dilute sodium hydroxide until the reaction is almost neutral to litmus, but still slightly acid. Add a small quantity of fresh yeast, and gently shake so as to break up the yeast. With the emulsion of yeast in the glucose solution fill the closed limb of a fermentation tube, so that no air bubble is left, and place the tube for about an hour in a warm water-bath at 40° C. What takes place ? (b) Put the fermentation tube into the cupboard. After twenty-four hours remove the solution and filter. Examine the filtrate for alcohol by means of the iodoform test and the bichromate test. [Tests for alcohol—(a) Iodoform test. To the solution add a solution of iodine in potassium iodide until it is brown, then add just sufficient sodium hydroxide to decolorise the mixture. Warm gently. A yellow crystalline precipitate with the characteristic smell of
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