Fig. 33.—Evolution of Gases from Pure Cultivation of B. Furfuris.
In a second fermentation (III.) we endeavoured to ascertain the exact amount of CO2 evolved, as in the previous fermentation this had not been done. It was therefore decided to absorb the CO2 by means of potash.
The fermentation in this case was conducted in a narrow-necked flask of 2000 c.c. capacity, connected by means of a narrow glass tube with two potash bulbs containing strong caustic potash, and furnished with a delivery tube dipping under water; the whole apparatus stood upon an iron plate, and was maintained at a temperature of 25°–30° in the same manner as the previous fermentation. The gases were evolved for 21 days—a considerably shorter period than the 1000 c.c. fermentation; but resembling it in that one-half the gas was evolved in eight days. The diagram shows the curve as in the previous fermentation, which it resembles for the first 14 days, afterwards however stopping suddenly. When the fermentation was at an end the flask and contents were heated to boiling point, at the same time a current of air free from CO2 was drawn through it, and the CO2 given off being collected in potash bulbs as in the fermentation. Unfortunately the estimation of the CO2 was rendered valueless owing to an accident.
The table shows the composition of the gases other than CO2 evolved in this second fermentation.
Gases from Fermentation of 2000 c.c. (excluding CO2)
Fermentation III.
— | Days | Mean | |||||
2–4 | 4–5 | 5–6 | 11 | 14–15 | 16–17 | ||
| O2 | 3·4 | 2·2 | 1·5 | 0·42 | 0·9 | 2·4 | 1·48 |
| H2 | 81·3 | 83·3 | 82·4 | 79·0 | 71·7 | 72·2 | 77·72 |
| N2 | 15·3 | 14·5 | 16·1 | 20·5 | 27·4 | 25·4 | 20·78 |
The gas from days 18–21 was unfortunately mixed with air. On comparing the mean composition of gases other than CO2 collected from both fermentations, we get the following result:—
| — | Fermentation, 1000 c.c. | Fermentation, 2000 c.c. |
| O2 | 3·57 | 1·48 |
| H2 | 69·4 | 77·72 |
| N2 | 27·0 | 20·78 |
If now the O and part of the N in the proportion to form air be taken away, the composition of the gases from the two fermentations is found to be almost exactly similar:—
| — | Fermentation, 1000 c.c. | Fermentation, 2000 c.c. |
| H2 | 84·4 | 83·9 |
| N2 | 15·6 | 16·1 |
| 100.0 | 100.0 |