In the closed fermentations we had previously collected only small quantities of gas over mercury, owing to the difficulty of continuously collecting large quantities which came off during the night. In the fermentation of September 16, 1894, we collected the whole of the gas given off, taking samples every day over mercury, the gas coming off at night being collected over warm water. Of course this method does not give the total amount of gas evolved with absolute accuracy, but the exact composition of the gases was known from day to day, and the amount of CO_{2} absorbed by the water could be calculated with moderate accuracy. The fermentation was conducted in a narrow-necked litre flask fitted with a narrow delivery tube dipping under mercury, and sterilised with all the usual precautions. The temperature was maintained at 25°–30°, gas was evolved for 39 days, when it ceased to come off, the total amount collected being 3435 c.c. One-half of this quantity, however, came off in seven days. About 300 c.c. of CO_{2} was absorbed by the water during the whole period. The diagram (Fig. 33) shows the manner of evolution of the gases, the ordinates representing volume of gas and the abscissæ lapse of time after inoculation. The following table shows the composition of the gas at different stages of the fermentation. (The fermentation (II.) is the one of which the chemical analysis has been previously given, page 273):-- COMPOSITION OF GASES EVOLVED IN FERMENTATION OF 1000 C.C. GLUCOSE WITH PURE FERMENT. SEPTEMBER 16, 1894. +-------+-----------------------------------------+----- | | Day | + -- +------+------+------+------+------+------+ Mean | | 5 | 9 | 12 | 19 |26–31 |35–39 | +-------+------+------+------+------+------+------+----- |CO_{2} | 53·7 | 56·4 | 44·3 | 52·6 | 55·6 | 43·2 | 49·9 |O_{2} | 1·8 | 0·5 | 1·7 | 1·9 | 0·8 | 2·8 | 1·8 |H_{2} | 35·8 | 34·6 | 41·2 | 30·3 | 34·7 | 31·8 | 34·8 |N_{2} | 8·7 | 8·5 | 12·8 | 15·2 | 8·9 | 22·2 | 13·5 +-------+------+------+------+------+------+------+----- The total quantity of CO_{2} actually collected = 1563 c.c. = 3·090 grm.; the amount of CO_{2} due to decomposition of the CaCO_{3} by the acids produced was found to be 667 c.c. = (1·3189 grm). The vol. of hydrogen collected was 1086 c.c. = 0·973 grm. [Illustration: Fig. 33.--Evolution of Gases from Pure Cultivation of B. Furfuris.] In a second fermentation (III.) we endeavoured to ascertain the exact amount of CO_{2} evolved, as in the previous fermentation this had not been done. It was therefore decided to absorb the CO_{2} by means of potash.