Practical bacteriology for chemical students / by David Ellis.

  • David Ellis
Date:
1923
Catalogue details

Licence: In copyright

Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.

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    4. Replace the stopper, make air-tight and put whole ap- paratus away in incubator at 30 0 C. 5. Examine after 24 hours. The test-tube will be full of a gas given off during the fermentation of Yeast in Pasteur’s fluid. Exercise 93. Examination of gas given off during fermenta- tion of Yeast. 1. Collect some of the gas given off during the fermenta- tion of Yeast in Pasteur's fluid (Exerc. 92) in a test- tube over water (Fig. 39). 2. By means of a curved pipette introduce a few c.c. of caustic potash solution. Note the rise of the water in the test-tube due to the absorption of the gas by the caustic potash. This proves that the gas is carbon dioxide which is very soluble in caustic potash.* Exercise 94. Production of alcohol in Yeast fermentation. Remove the cork from the flask in which Yeast-fer- mentation is going on (Exercise 92). A faint but distinct alcoholic odour is manifested. Test as follows (Klocker Method). 1. Place 5 c.c. of fermenting fluid in a vessel about 180 m.m. long and 24 m.m. diameter. 2. Warm slowly over a wire gauze by means of a gas flame taking care to prevent bumping. Characteristic oil drops accumulate in the glass tubing higher up or lower down according to the concentration of the alcohol. Pure Cultures of Yeast. The methods of pure culture which have been described for the isolation and cultivation of 'bacteria may be applied with equal1 success to the Yeast family. Exercise 95. Pure Culture of Yeast. 1. Obtain a little distiller’s or brewer’s yeast or some barm from a baker. * The lime water test for this gas should also be applied.